Array API
=========
.. sectionauthor:: Travis E. Oliphant
| The test of a first-rate intelligence is the ability to hold two
| opposed ideas in the mind at the same time, and still retain the
| ability to function.
| --- *F. Scott Fitzgerald*
| For a successful technology, reality must take precedence over public
| relations, for Nature cannot be fooled.
| --- *Richard P. Feynman*
.. index::
pair: ndarray; C-API
pair: C-API; array
Array structure and data access
-------------------------------
These macros all access the :ctype:`PyArrayObject` structure members. The input
argument, obj, can be any :ctype:`PyObject *` that is directly interpretable
as a :ctype:`PyArrayObject *` (any instance of the :cdata:`PyArray_Type` and its
sub-types).
.. cfunction:: void *PyArray_DATA(PyObject *obj)
.. cfunction:: char *PyArray_BYTES(PyObject *obj)
These two macros are similar and obtain the pointer to the
data-buffer for the array. The first macro can (and should be)
assigned to a particular pointer where the second is for generic
processing. If you have not guaranteed a contiguous and/or aligned
array then be sure you understand how to access the data in the
array to avoid memory and/or alignment problems.
.. cfunction:: npy_intp *PyArray_DIMS(PyObject *arr)
.. cfunction:: npy_intp *PyArray_STRIDES(PyObject* arr)
.. cfunction:: npy_intp PyArray_DIM(PyObject* arr, int n)
Return the shape in the *n* :math:`^{\textrm{th}}` dimension.
.. cfunction:: npy_intp PyArray_STRIDE(PyObject* arr, int n)
Return the stride in the *n* :math:`^{\textrm{th}}` dimension.
.. cfunction:: PyObject *PyArray_BASE(PyObject* arr)
.. cfunction:: PyArray_Descr *PyArray_DESCR(PyObject* arr)
.. cfunction:: int PyArray_FLAGS(PyObject* arr)
.. cfunction:: int PyArray_ITEMSIZE(PyObject* arr)
Return the itemsize for the elements of this array.
.. cfunction:: int PyArray_TYPE(PyObject* arr)
Return the (builtin) typenumber for the elements of this array.
.. cfunction:: PyObject *PyArray_GETITEM(PyObject* arr, void* itemptr)
Get a Python object from the ndarray, *arr*, at the location
pointed to by itemptr. Return ``NULL`` on failure.
.. cfunction:: int PyArray_SETITEM(PyObject* arr, void* itemptr, PyObject* obj)
Convert obj and place it in the ndarray, *arr*, at the place
pointed to by itemptr. Return -1 if an error occurs or 0 on
success.
.. cfunction:: npy_intp PyArray_SIZE(PyObject* arr)
Returns the total size (in number of elements) of the array.
.. cfunction:: npy_intp PyArray_Size(PyObject* obj)
Returns 0 if *obj* is not a sub-class of bigndarray. Otherwise,
returns the total number of elements in the array. Safer version
of :cfunc:`PyArray_SIZE` (*obj*).
.. cfunction:: npy_intp PyArray_NBYTES(PyObject* arr)
Returns the total number of bytes consumed by the array.
Data access
^^^^^^^^^^^
These functions and macros provide easy access to elements of the
ndarray from C. These work for all arrays. You may need to take care
when accessing the data in the array, however, if it is not in machine
byte-order, misaligned, or not writeable. In other words, be sure to
respect the state of the flags unless you know what you are doing, or
have previously guaranteed an array that is writeable, aligned, and in
machine byte-order using :cfunc:`PyArray_FromAny`. If you wish to handle all
types of arrays, the copyswap function for each type is useful for
handling misbehaved arrays. Some platforms (e.g. Solaris) do not like
misaligned data and will crash if you de-reference a misaligned
pointer. Other platforms (e.g. x86 Linux) will just work more slowly
with misaligned data.
.. cfunction:: void* PyArray_GetPtr(PyArrayObject* aobj, npy_intp* ind)
Return a pointer to the data of the ndarray, *aobj*, at the
N-dimensional index given by the c-array, *ind*, (which must be
at least *aobj* ->nd in size). You may want to typecast the
returned pointer to the data type of the ndarray.
.. cfunction:: void* PyArray_GETPTR1(PyObject* obj, i)
.. cfunction:: void* PyArray_GETPTR2(PyObject* obj, i, j)
.. cfunction:: void* PyArray_GETPTR3(PyObject* obj, i, j, k)
.. cfunction:: void* PyArray_GETPTR4(PyObject* obj, i, j, k, l)
Quick, inline access to the element at the given coordinates in
the ndarray, *obj*, which must have respectively 1, 2, 3, or 4
dimensions (this is not checked). The corresponding *i*, *j*,
*k*, and *l* coordinates can be any integer but will be
interpreted as ``npy_intp``. You may want to typecast the
returned pointer to the data type of the ndarray.
Creating arrays
---------------
From scratch
^^^^^^^^^^^^
.. cfunction:: PyObject* PyArray_NewFromDescr(PyTypeObject* subtype, PyArray_Descr* descr, int nd, npy_intp* dims, npy_intp* strides, void* data, int flags, PyObject* obj)
This is the main array creation function. Most new arrays are
created with this flexible function. The returned object is an
object of Python-type *subtype*, which must be a subtype of
:cdata:`PyArray_Type`. The array has *nd* dimensions, described by
*dims*. The data-type descriptor of the new array is *descr*. If
*subtype* is not :cdata:`&PyArray_Type` (*e.g.* a Python subclass of
the ndarray), then *obj* is the object to pass to the
:obj:`__array_finalize__` method of the subclass. If *data* is
``NULL``, then new memory will be allocated and *flags* can be
non-zero to indicate a Fortran-style contiguous array. If *data*
is not ``NULL``, then it is assumed to point to the memory to be
used for the array and the *flags* argument is used as the new
flags for the array (except the state of :cdata:`NPY_OWNDATA` and
:cdata:`UPDATEIFCOPY` flags of the new array will be reset). In
addition, if *data* is non-NULL, then *strides* can also be
provided. If *strides* is ``NULL``, then the array strides are
computed as C-style contiguous (default) or Fortran-style
contiguous (*flags* is nonzero for *data* = ``NULL`` or *flags* &
:cdata:`NPY_F_CONTIGUOUS` is nonzero non-NULL *data*). Any provided
*dims* and *strides* are copied into newly allocated dimension and
strides arrays for the new array object.
.. cfunction:: PyObject* PyArray_New(PyTypeObject* subtype, int nd, npy_intp* dims, int type_num, npy_intp* strides, void* data, int itemsize, int flags, PyObject* obj)
This is similar to :cfunc:`PyArray_DescrNew` (...) except you
specify the data-type descriptor with *type_num* and *itemsize*,
where *type_num* corresponds to a builtin (or user-defined)
type. If the type always has the same number of bytes, then
itemsize is ignored. Otherwise, itemsize specifies the particular
size of this array.
.. warning::
If data is passed to :cfunc:`PyArray_NewFromDescr` or :cfunc:`PyArray_New`,
this memory must not be deallocated until the new array is
deleted. If this data came from another Python object, this can
be accomplished using :cfunc:`Py_INCREF` on that object and setting the
base member of the new array to point to that object. If strides
are passed in they must be consistent with the dimensions, the
itemsize, and the data of the array.
.. cfunction:: PyObject* PyArray_SimpleNew(int nd, npy_intp* dims, int typenum)
Create a new unitialized array of type, *typenum*, whose size in
each of *nd* dimensions is given by the integer array, *dims*.
This function cannot be used to create a flexible-type array (no
itemsize given).
.. cfunction:: PyObject* PyArray_SimpleNewFromData(int nd, npy_intp* dims, int typenum, void* data)
Create an array wrapper around *data* pointed to by the given
pointer. The array flags will have a default that the data area is
well-behaved and C-style contiguous. The shape of the array is
given by the *dims* c-array of length *nd*. The data-type of the
array is indicated by *typenum*.
.. cfunction:: PyObject* PyArray_SimpleNewFromDescr(int nd, npy_intp* dims, PyArray_Descr* descr)
Create a new array with the provided data-type descriptor, *descr*
, of the shape deteremined by *nd* and *dims*.
.. cfunction:: PyArray_FILLWBYTE(PyObject* obj, int val)
Fill the array pointed to by *obj* ---which must be a (subclass
of) bigndarray---with the contents of *val* (evaluated as a byte).
.. cfunction:: PyObject* PyArray_Zeros(int nd, npy_intp* dims, PyArray_Descr* dtype, int fortran)
Construct a new *nd* -dimensional array with shape given by *dims*
and data type given by *dtype*. If *fortran* is non-zero, then a
Fortran-order array is created, otherwise a C-order array is
created. Fill the memory with zeros (or the 0 object if *dtype*
corresponds to :ctype:`PyArray_OBJECT` ).
.. cfunction:: PyObject* PyArray_ZEROS(int nd, npy_intp* dims, int type_num, int fortran)
Macro form of :cfunc:`PyArray_Zeros` which takes a type-number instead
of a data-type object.
.. cfunction:: PyObject* PyArray_Empty(int nd, npy_intp* dims, PyArray_Descr* dtype, int fortran)
Construct a new *nd* -dimensional array with shape given by *dims*
and data type given by *dtype*. If *fortran* is non-zero, then a
Fortran-order array is created, otherwise a C-order array is
created. The array is uninitialized unless the data type
corresponds to :ctype:`PyArray_OBJECT` in which case the array is
filled with :cdata:`Py_None`.
.. cfunction:: PyObject* PyArray_EMPTY(int nd, npy_intp* dims, int typenum, int fortran)
Macro form of :cfunc:`PyArray_Empty` which takes a type-number,
*typenum*, instead of a data-type object.
.. cfunction:: PyObject* PyArray_Arange(double start, double stop, double step, int typenum)
Construct a new 1-dimensional array of data-type, *typenum*, that
ranges from *start* to *stop* (exclusive) in increments of *step*
. Equivalent to **arange** (*start*, *stop*, *step*, dtype).
.. cfunction:: PyObject* PyArray_ArangeObj(PyObject* start, PyObject* stop, PyObject* step, PyArray_Descr* descr)
Construct a new 1-dimensional array of data-type determined by
``descr``, that ranges from ``start`` to ``stop`` (exclusive) in
increments of ``step``. Equivalent to arange( ``start``,
``stop``, ``step``, ``typenum`` ).
From other objects
^^^^^^^^^^^^^^^^^^
.. cfunction:: PyObject* PyArray_FromAny(PyObject* op, PyArray_Descr* dtype, int min_depth, int max_depth, int requirements, PyObject* context)
This is the main function used to obtain an array from any nested
sequence, or object that exposes the array interface, *op*. The
parameters allow specification of the required *dtype*, the
minimum (*min_depth*) and maximum (*max_depth*) number of
dimensions acceptable, and other *requirements* for the array. The
*dtype* argument needs to be a :ctype:`PyArray_Descr` structure
indicating the desired data-type (including required
byteorder). The *dtype* argument may be NULL, indicating that any
data-type (and byteorder) is acceptable. Unless ``FORCECAST`` is
present in ``flags``, this call will generate an error if the data
type cannot be safely obtained from the object. If you want to use
``NULL`` for the *dtype* and ensure the array is notswapped then
use :cfunc:`PyArray_CheckFromAny`. A value of 0 for either of the
depth parameters causes the parameter to be ignored. Any of the
following array flags can be added (*e.g.* using \|) to get the
*requirements* argument. If your code can handle general (*e.g.*
strided, byte-swapped, or unaligned arrays) then *requirements*
may be 0. Also, if *op* is not already an array (or does not
expose the array interface), then a new array will be created (and
filled from *op* using the sequence protocol). The new array will
have :cdata:`NPY_DEFAULT` as its flags member. The *context* argument
is passed to the :obj:`__array__` method of *op* and is only used if
the array is constructed that way. Almost always this
parameter is ``NULL``.
.. cvar:: NPY_C_CONTIGUOUS
Make sure the returned array is C-style contiguous
.. cvar:: NPY_F_CONTIGUOUS
Make sure the returned array is Fortran-style contiguous.
.. cvar:: NPY_ALIGNED
Make sure the returned array is aligned on proper boundaries for its
data type. An aligned array has the data pointer and every strides
factor as a multiple of the alignment factor for the data-type-
descriptor.
.. cvar:: NPY_WRITEABLE
Make sure the returned array can be written to.
.. cvar:: NPY_ENSURECOPY
Make sure a copy is made of *op*. If this flag is not
present, data is not copied if it can be avoided.
.. cvar:: NPY_ENSUREARRAY
Make sure the result is a base-class ndarray or bigndarray. By
default, if *op* is an instance of a subclass of the
bigndarray, an instance of that same subclass is returned. If
this flag is set, an ndarray object will be returned instead.
.. cvar:: NPY_FORCECAST
Force a cast to the output type even if it cannot be done
safely. Without this flag, a data cast will occur only if it
can be done safely, otherwise an error is reaised.
.. cvar:: NPY_UPDATEIFCOPY
If *op* is already an array, but does not satisfy the
requirements, then a copy is made (which will satisfy the
requirements). If this flag is present and a copy (of an
object that is already an array) must be made, then the
corresponding :cdata:`NPY_UPDATEIFCOPY` flag is set in the returned
copy and *op* is made to be read-only. When the returned copy
is deleted (presumably after your calculations are complete),
its contents will be copied back into *op* and the *op* array
will be made writeable again. If *op* is not writeable to
begin with, then an error is raised. If *op* is not already an
array, then this flag has no effect.
.. cvar:: NPY_BEHAVED
:cdata:`NPY_ALIGNED` \| :cdata:`NPY_WRITEABLE`
.. cvar:: NPY_CARRAY
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_BEHAVED`
.. cvar:: NPY_CARRAY_RO
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_FARRAY
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_BEHAVED`
.. cvar:: NPY_FARRAY_RO
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_DEFAULT
:cdata:`NPY_CARRAY`
.. cvar:: NPY_IN_ARRAY
:cdata:`NPY_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_IN_FARRAY
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_INOUT_ARRAY
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_WRITEABLE` \|
:cdata:`NPY_ALIGNED`
.. cvar:: NPY_INOUT_FARRAY
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_WRITEABLE` \|
:cdata:`NPY_ALIGNED`
.. cvar:: NPY_OUT_ARRAY
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_WRITEABLE` \|
:cdata:`NPY_ALIGNED` \| :cdata:`NPY_UPDATEIFCOPY`
.. cvar:: NPY_OUT_FARRAY
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_WRITEABLE` \|
:cdata:`NPY_ALIGNED` \| :cdata:`UPDATEIFCOPY`
.. cfunction:: PyObject* PyArray_CheckFromAny(PyObject* op, PyArray_Descr* dtype, int min_depth, int max_depth, int requirements, PyObject* context)
Nearly identical to :cfunc:`PyArray_FromAny` (...) except
*requirements* can contain :cdata:`NPY_NOTSWAPPED` (over-riding the
specification in *dtype*) and :cdata:`NPY_ELEMENTSTRIDES` which
indicates that the array should be aligned in the sense that the
strides are multiples of the element size.
.. cvar:: NPY_NOTSWAPPED
Make sure the returned array has a data-type descriptor that is in
machine byte-order, over-riding any specification in the *dtype*
argument. Normally, the byte-order requirement is determined by
the *dtype* argument. If this flag is set and the dtype argument
does not indicate a machine byte-order descriptor (or is NULL and
the object is already an array with a data-type descriptor that is
not in machine byte- order), then a new data-type descriptor is
created and used with its byte-order field set to native.
.. cvar:: NPY_BEHAVED_NS
:cdata:`NPY_ALIGNED` \| :cdata:`NPY_WRITEABLE` \| :cdata:`NPY_NOTSWAPPED`
.. cvar:: NPY_ELEMENTSTRIDES
Make sure the returned array has strides that are multiples of the
element size.
.. cfunction:: PyObject* PyArray_FromArray(PyArrayObject* op, PyArray_Descr* newtype, int requirements)
Special case of :cfunc:`PyArray_FromAny` for when *op* is already an
array but it needs to be of a specific *newtype* (including
byte-order) or has certain *requirements*.
.. cfunction:: PyObject* PyArray_FromStructInterface(PyObject* op)
Returns an ndarray object from a Python object that exposes the
:obj:`__array_struct__`` method and follows the array interface
protocol. If the object does not contain this method then a
borrowed reference to :cdata:`Py_NotImplemented` is returned.
.. cfunction:: PyObject* PyArray_FromInterface(PyObject* op)
Returns an ndarray object from a Python object that exposes the
:obj:`__array_shape__` and :obj:`__array_typestr__`
methods following
the array interface protocol. If the object does not contain one
of these method then a borrowed reference to :cdata:`Py_NotImplemented`
is returned.
.. cfunction:: PyObject* PyArray_FromArrayAttr(PyObject* op, PyArray_Descr* dtype, PyObject* context)
Return an ndarray object from a Python object that exposes the
:obj:`__array__` method. The :obj:`__array__` method can take 0, 1, or 2
arguments ([dtype, context]) where *context* is used to pass
information about where the :obj:`__array__` method is being called
from (currently only used in ufuncs).
.. cfunction:: PyObject* PyArray_ContiguousFromAny(PyObject* op, int typenum, int min_depth, int max_depth)
This function returns a (C-style) contiguous and behaved function
array from any nested sequence or array interface exporting
object, *op*, of (non-flexible) type given by the enumerated
*typenum*, of minimum depth *min_depth*, and of maximum depth
*max_depth*. Equivalent to a call to :cfunc:`PyArray_FromAny` with
requirements set to :cdata:`NPY_DEFAULT` and the type_num member of the
type argument set to *typenum*.
.. cfunction:: PyObject *PyArray_FromObject(PyObject *op, int typenum, int min_depth, int max_depth)
Return an aligned and in native-byteorder array from any nested
sequence or array-interface exporting object, op, of a type given by
the enumerated typenum. The minimum number of dimensions the array can
have is given by min_depth while the maximum is max_depth. This is
equivalent to a call to :cfunc:`PyArray_FromAny` with requirements set to
BEHAVED.
.. cfunction:: PyObject* PyArray_EnsureArray(PyObject* op)
This function **steals a reference** to ``op`` and makes sure that
``op`` is a base-class ndarray. It special cases array scalars,
but otherwise calls :cfunc:`PyArray_FromAny` ( ``op``, NULL, 0, 0,
:cdata:`NPY_ENSUREARRAY`).
.. cfunction:: PyObject* PyArray_FromString(char* string, npy_intp slen, PyArray_Descr* dtype, npy_intp num, char* sep)
Construct a one-dimensional ndarray of a single type from a binary
or (ASCII) text ``string`` of length ``slen``. The data-type of
the array to-be-created is given by ``dtype``. If num is -1, then
**copy** the entire string and return an appropriately sized
array, otherwise, ``num`` is the number of items to **copy** from
the string. If ``sep`` is NULL (or ""), then interpret the string
as bytes of binary data, otherwise convert the sub-strings
separated by ``sep`` to items of data-type ``dtype``. Some
data-types may not be readable in text mode and an error will be
raised if that occurs. All errors return NULL.
.. cfunction:: PyObject* PyArray_FromFile(FILE* fp, PyArray_Descr* dtype, npy_intp num, char* sep)
Construct a one-dimensional ndarray of a single type from a binary
or text file. The open file pointer is ``fp``, the data-type of
the array to be created is given by ``dtype``. This must match
the data in the file. If ``num`` is -1, then read until the end of
the file and return an appropriately sized array, otherwise,
``num`` is the number of items to read. If ``sep`` is NULL (or
""), then read from the file in binary mode, otherwise read from
the file in text mode with ``sep`` providing the item
separator. Some array types cannot be read in text mode in which
case an error is raised.
.. cfunction:: PyObject* PyArray_FromBuffer(PyObject* buf, PyArray_Descr* dtype, npy_intp count, npy_intp offset)
Construct a one-dimensional ndarray of a single type from an
object, ``buf``, that exports the (single-segment) buffer protocol
(or has an attribute __buffer\__ that returns an object that
exports the buffer protocol). A writeable buffer will be tried
first followed by a read- only buffer. The :cdata:`NPY_WRITEABLE`
flag of the returned array will reflect which one was
successful. The data is assumed to start at ``offset`` bytes from
the start of the memory location for the object. The type of the
data in the buffer will be interpreted depending on the data- type
descriptor, ``dtype.`` If ``count`` is negative then it will be
determined from the size of the buffer and the requested itemsize,
otherwise, ``count`` represents how many elements should be
converted from the buffer.
.. cfunction:: int PyArray_CopyInto(PyArrayObject* dest, PyArrayObject* src)
Copy from the source array, ``src``, into the destination array,
``dest``, performing a data-type conversion if necessary. If an
error occurs return -1 (otherwise 0). The shape of ``src`` must be
broadcastable to the shape of ``dest``. The data areas of dest
and src must not overlap.
.. cfunction:: int PyArray_MoveInto(PyArrayObject* dest, PyArrayObject* src)
Move data from the source array, ``src``, into the destination
array, ``dest``, performing a data-type conversion if
necessary. If an error occurs return -1 (otherwise 0). The shape
of ``src`` must be broadcastable to the shape of ``dest``. The
data areas of dest and src may overlap.
.. cfunction:: PyArrayObject* PyArray_GETCONTIGUOUS(PyObject* op)
If ``op`` is already (C-style) contiguous and well-behaved then
just return a reference, otherwise return a (contiguous and
well-behaved) copy of the array. The parameter op must be a
(sub-class of an) ndarray and no checking for that is done.
.. cfunction:: PyObject* PyArray_FROM_O(PyObject* obj)
Convert ``obj`` to an ndarray. The argument can be any nested
sequence or object that exports the array interface. This is a
macro form of :cfunc:`PyArray_FromAny` using ``NULL``, 0, 0, 0 for the
other arguments. Your code must be able to handle any data-type
descriptor and any combination of data-flags to use this macro.
.. cfunction:: PyObject* PyArray_FROM_OF(PyObject* obj, int requirements)
Similar to :cfunc:`PyArray_FROM_O` except it can take an argument
of *requirements* indicating properties the resulting array must
have. Available requirements that can be enforced are
:cdata:`NPY_CONTIGUOUS`, :cdata:`NPY_F_CONTIGUOUS`,
:cdata:`NPY_ALIGNED`, :cdata:`NPY_WRITEABLE`,
:cdata:`NPY_NOTSWAPPED`, :cdata:`NPY_ENSURECOPY`,
:cdata:`NPY_UPDATEIFCOPY`, :cdata:`NPY_FORCECAST`, and
:cdata:`NPY_ENSUREARRAY`. Standard combinations of flags can also
be used:
.. cfunction:: PyObject* PyArray_FROM_OT(PyObject* obj, int typenum)
Similar to :cfunc:`PyArray_FROM_O` except it can take an argument of
*typenum* specifying the type-number the returned array.
.. cfunction:: PyObject* PyArray_FROM_OTF(PyObject* obj, int typenum, int requirements)
Combination of :cfunc:`PyArray_FROM_OF` and :cfunc:`PyArray_FROM_OT`
allowing both a *typenum* and a *flags* argument to be provided..
.. cfunction:: PyObject* PyArray_FROMANY(PyObject* obj, int typenum, int min, int max, int requirements)
Similar to :cfunc:`PyArray_FromAny` except the data-type is
specified using a typenumber. :cfunc:`PyArray_DescrFromType`
(*typenum*) is passed directly to :cfunc:`PyArray_FromAny`. This
macro also adds :cdata:`NPY_DEFAULT` to requirements if
:cdata:`NPY_ENSURECOPY` is passed in as requirements.
.. cfunction:: PyObject *PyArray_CheckAxis(PyObject* obj, int* axis, int requirements)
Encapsulate the functionality of functions and methods that take
the axis= keyword and work properly with None as the axis
argument. The input array is ``obj``, while ``*axis`` is a
converted integer (so that >=MAXDIMS is the None value), and
``requirements`` gives the needed properties of ``obj``. The
output is a converted version of the input so that requirements
are met and if needed a flattening has occurred. On output
negative values of ``*axis`` are converted and the new value is
checked to ensure consistency with the shape of ``obj``.
Dealing with types
------------------
General check of Python Type
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. cfunction:: PyArray_Check(op)
Evaluates true if *op* is a Python object whose type is a sub-type
of :cdata:`PyArray_Type`.
.. cfunction:: PyArray_CheckExact(op)
Evaluates true if *op* is a Python object with type
:cdata:`PyArray_Type`.
.. cfunction:: PyArray_HasArrayInterface(op, out)
If ``op`` implements any part of the array interface, then ``out``
will contain a new reference to the newly created ndarray using
the interface or ``out`` will contain ``NULL`` if an error during
conversion occurs. Otherwise, out will contain a borrowed
reference to :cdata:`Py_NotImplemented` and no error condition is set.
.. cfunction:: PyArray_HasArrayInterfaceType(op, type, context, out)
If ``op`` implements any part of the array interface, then ``out``
will contain a new reference to the newly created ndarray using
the interface or ``out`` will contain ``NULL`` if an error during
conversion occurs. Otherwise, out will contain a borrowed
reference to Py_NotImplemented and no error condition is set.
This version allows setting of the type and context in the part of
the array interface that looks for the :obj:`__array__` attribute.
.. cfunction:: PyArray_IsZeroDim(op)
Evaluates true if *op* is an instance of (a subclass of)
:cdata:`PyArray_Type` and has 0 dimensions.
.. cfunction:: PyArray_IsScalar(op, cls)
Evaluates true if *op* is an instance of :cdata:`Py{cls}ArrType_Type`.
.. cfunction:: PyArray_CheckScalar(op)
Evaluates true if *op* is either an array scalar (an instance of a
sub-type of :cdata:`PyGenericArr_Type` ), or an instance of (a
sub-class of) :cdata:`PyArray_Type` whose dimensionality is 0.
.. cfunction:: PyArray_IsPythonScalar(op)
Evaluates true if *op* is a builtin Python "scalar" object (int,
float, complex, str, unicode, long, bool).
.. cfunction:: PyArray_IsAnyScalar(op)
Evaluates true if *op* is either a Python scalar or an array
scalar (an instance of a sub- type of :cdata:`PyGenericArr_Type` ).
Data-type checking
^^^^^^^^^^^^^^^^^^
For the typenum macros, the argument is an integer representing an
enumerated array data type. For the array type checking macros the
argument must be a :ctype:`PyObject *` that can be directly interpreted as a
:ctype:`PyArrayObject *`.
.. cfunction:: PyTypeNum_ISUNSIGNED(num)
.. cfunction:: PyDataType_ISUNSIGNED(descr)
.. cfunction:: PyArray_ISUNSIGNED(obj)
Type represents an unsigned integer.
.. cfunction:: PyTypeNum_ISSIGNED(num)
.. cfunction:: PyDataType_ISSIGNED(descr)
.. cfunction:: PyArray_ISSIGNED(obj)
Type represents a signed integer.
.. cfunction:: PyTypeNum_ISINTEGER(num)
.. cfunction:: PyDataType_ISINTEGER(descr)
.. cfunction:: PyArray_ISINTEGER(obj)
Type represents any integer.
.. cfunction:: PyTypeNum_ISFLOAT(num)
.. cfunction:: PyDataType_ISFLOAT(descr)
.. cfunction:: PyArray_ISFLOAT(obj)
Type represents any floating point number.
.. cfunction:: PyTypeNum_ISCOMPLEX(num)
.. cfunction:: PyDataType_ISCOMPLEX(descr)
.. cfunction:: PyArray_ISCOMPLEX(obj)
Type represents any complex floating point number.
.. cfunction:: PyTypeNum_ISNUMBER(num)
.. cfunction:: PyDataType_ISNUMBER(descr)
.. cfunction:: PyArray_ISNUMBER(obj)
Type represents any integer, floating point, or complex floating point
number.
.. cfunction:: PyTypeNum_ISSTRING(num)
.. cfunction:: PyDataType_ISSTRING(descr)
.. cfunction:: PyArray_ISSTRING(obj)
Type represents a string data type.
.. cfunction:: PyTypeNum_ISPYTHON(num)
.. cfunction:: PyDataType_ISPYTHON(descr)
.. cfunction:: PyArray_ISPYTHON(obj)
Type represents an enumerated type corresponding to one of the
standard Python scalar (bool, int, float, or complex).
.. cfunction:: PyTypeNum_ISFLEXIBLE(num)
.. cfunction:: PyDataType_ISFLEXIBLE(descr)
.. cfunction:: PyArray_ISFLEXIBLE(obj)
Type represents one of the flexible array types ( :cdata:`NPY_STRING`,
:cdata:`NPY_UNICODE`, or :cdata:`NPY_VOID` ).
.. cfunction:: PyTypeNum_ISUSERDEF(num)
.. cfunction:: PyDataType_ISUSERDEF(descr)
.. cfunction:: PyArray_ISUSERDEF(obj)
Type represents a user-defined type.
.. cfunction:: PyTypeNum_ISEXTENDED(num)
.. cfunction:: PyDataType_ISEXTENDED(descr)
.. cfunction:: PyArray_ISEXTENDED(obj)
Type is either flexible or user-defined.
.. cfunction:: PyTypeNum_ISOBJECT(num)
.. cfunction:: PyDataType_ISOBJECT(descr)
.. cfunction:: PyArray_ISOBJECT(obj)
Type represents object data type.
.. cfunction:: PyTypeNum_ISBOOL(num)
.. cfunction:: PyDataType_ISBOOL(descr)
.. cfunction:: PyArray_ISBOOL(obj)
Type represents Boolean data type.
.. cfunction:: PyDataType_HASFIELDS(descr)
.. cfunction:: PyArray_HASFIELDS(obj)
Type has fields associated with it.
.. cfunction:: PyArray_ISNOTSWAPPED(m)
Evaluates true if the data area of the ndarray *m* is in machine
byte-order according to the array's data-type descriptor.
.. cfunction:: PyArray_ISBYTESWAPPED(m)
Evaluates true if the data area of the ndarray *m* is **not** in
machine byte-order according to the array's data-type descriptor.
.. cfunction:: Bool PyArray_EquivTypes(PyArray_Descr* type1, PyArray_Descr* type2)
Return :cdata:`NPY_TRUE` if *type1* and *type2* actually represent
equivalent types for this platform (the fortran member of each
type is ignored). For example, on 32-bit platforms,
:cdata:`NPY_LONG` and :cdata:`NPY_INT` are equivalent. Otherwise
return :cdata:`NPY_FALSE`.
.. cfunction:: Bool PyArray_EquivArrTypes(PyArrayObject* a1, PyArrayObject * a2)
Return :cdata:`NPY_TRUE` if *a1* and *a2* are arrays with equivalent
types for this platform.
.. cfunction:: Bool PyArray_EquivTypenums(int typenum1, int typenum2)
Special case of :cfunc:`PyArray_EquivTypes` (...) that does not accept
flexible data types but may be easier to call.
.. cfunction:: int PyArray_EquivByteorders({byteorder} b1, {byteorder} b2)
True if byteorder characters ( :cdata:`NPY_LITTLE`,
:cdata:`NPY_BIG`, :cdata:`NPY_NATIVE`, :cdata:`NPY_IGNORE` ) are
either equal or equivalent as to their specification of a native
byte order. Thus, on a little-endian machine :cdata:`NPY_LITTLE`
and :cdata:`NPY_NATIVE` are equivalent where they are not
equivalent on a big-endian machine.
Converting data types
^^^^^^^^^^^^^^^^^^^^^
.. cfunction:: PyObject* PyArray_Cast(PyArrayObject* arr, int typenum)
Mainly for backwards compatibility to the Numeric C-API and for
simple casts to non-flexible types. Return a new array object with
the elements of *arr* cast to the data-type *typenum* which must
be one of the enumerated types and not a flexible type.
.. cfunction:: PyObject* PyArray_CastToType(PyArrayObject* arr, PyArray_Descr* type, int fortran)
Return a new array of the *type* specified, casting the elements
of *arr* as appropriate. The fortran argument specifies the
ordering of the output array.
.. cfunction:: int PyArray_CastTo(PyArrayObject* out, PyArrayObject* in)
Cast the elements of the array *in* into the array *out*. The
output array should be writeable, have an integer-multiple of the
number of elements in the input array (more than one copy can be
placed in out), and have a data type that is one of the builtin
types. Returns 0 on success and -1 if an error occurs.
.. cfunction:: PyArray_VectorUnaryFunc* PyArray_GetCastFunc(PyArray_Descr* from, int totype)
Return the low-level casting function to cast from the given
descriptor to the builtin type number. If no casting function
exists return ``NULL`` and set an error. Using this function
instead of direct access to *from* ->f->cast will allow support of
any user-defined casting functions added to a descriptors casting
dictionary.
.. cfunction:: int PyArray_CanCastSafely(int fromtype, int totype)
Returns non-zero if an array of data type *fromtype* can be cast
to an array of data type *totype* without losing information. An
exception is that 64-bit integers are allowed to be cast to 64-bit
floating point values even though this can lose precision on large
integers so as not to proliferate the use of long doubles without
explict requests. Flexible array types are not checked according
to their lengths with this function.
.. cfunction:: int PyArray_CanCastTo(PyArray_Descr* fromtype, PyArray_Descr* totype)
Returns non-zero if an array of data type *fromtype* (which can
include flexible types) can be cast safely to an array of data
type *totype* (which can include flexible types). This is
basically a wrapper around :cfunc:`PyArray_CanCastSafely` with
additional support for size checking if *fromtype* and *totype*
are :cdata:`NPY_STRING` or :cdata:`NPY_UNICODE`.
.. cfunction:: int PyArray_ObjectType(PyObject* op, int mintype)
This function is useful for determining a common type that two or
more arrays can be converted to. It only works for non-flexible
array types as no itemsize information is passed. The *mintype*
argument represents the minimum type acceptable, and *op*
represents the object that will be converted to an array. The
return value is the enumerated typenumber that represents the
data-type that *op* should have.
.. cfunction:: void PyArray_ArrayType(PyObject* op, PyArray_Descr* mintype, PyArray_Descr* outtype)
This function works similarly to :cfunc:`PyArray_ObjectType` (...)
except it handles flexible arrays. The *mintype* argument can have
an itemsize member and the *outtype* argument will have an
itemsize member at least as big but perhaps bigger depending on
the object *op*.
.. cfunction:: PyArrayObject** PyArray_ConvertToCommonType(PyObject* op, int* n)
Convert a sequence of Python objects contained in *op* to an array
of ndarrays each having the same data type. The type is selected
based on the typenumber (larger type number is chosen over a
smaller one) ignoring objects that are only scalars. The length of
the sequence is returned in *n*, and an *n* -length array of
:ctype:`PyArrayObject` pointers is the return value (or ``NULL`` if an
error occurs). The returned array must be freed by the caller of
this routine (using :cfunc:`PyDataMem_FREE` ) and all the array objects
in it ``DECREF`` 'd or a memory-leak will occur. The example
template-code below shows a typically usage:
.. code-block:: c
mps = PyArray_ConvertToCommonType(obj, &n);
if (mps==NULL) return NULL;
{code}
for (i=0; iitemsize that
holds the representation of 0 for that type. The returned pointer,
*ret*, **must be freed** using :cfunc:`PyDataMem_FREE` (ret) when it is
not needed anymore.
.. cfunction:: char* PyArray_One(PyArrayObject* arr)
A pointer to newly created memory of size *arr* ->itemsize that
holds the representation of 1 for that type. The returned pointer,
*ret*, **must be freed** using :cfunc:`PyDataMem_FREE` (ret) when it
is not needed anymore.
.. cfunction:: int PyArray_ValidType(int typenum)
Returns :cdata:`NPY_TRUE` if *typenum* represents a valid type-number
(builtin or user-defined or character code). Otherwise, this
function returns :cdata:`NPY_FALSE`.
New data types
^^^^^^^^^^^^^^
.. cfunction:: void PyArray_InitArrFuncs(PyArray_ArrFuncs* f)
Initialize all function pointers and members to ``NULL``.
.. cfunction:: int PyArray_RegisterDataType(PyArray_Descr* dtype)
Register a data-type as a new user-defined data type for
arrays. The type must have most of its entries filled in. This is
not always checked and errors can produce segfaults. In
particular, the typeobj member of the ``dtype`` structure must be
filled with a Python type that has a fixed-size element-size that
corresponds to the elsize member of *dtype*. Also the ``f``
member must have the required functions: nonzero, copyswap,
copyswapn, getitem, setitem, and cast (some of the cast functions
may be ``NULL`` if no support is desired). To avoid confusion, you
should choose a unique character typecode but this is not enforced
and not relied on internally.
A user-defined type number is returned that uniquely identifies
the type. A pointer to the new structure can then be obtained from
:cfunc:`PyArray_DescrFromType` using the returned type number. A -1 is
returned if an error occurs. If this *dtype* has already been
registered (checked only by the address of the pointer), then
return the previously-assigned type-number.
.. cfunction:: int PyArray_RegisterCastFunc(PyArray_Descr* descr, int totype, PyArray_VectorUnaryFunc* castfunc)
Register a low-level casting function, *castfunc*, to convert
from the data-type, *descr*, to the given data-type number,
*totype*. Any old casting function is over-written. A ``0`` is
returned on success or a ``-1`` on failure.
.. cfunction:: int PyArray_RegisterCanCast(PyArray_Descr* descr, int totype, PyArray_SCALARKIND scalar)
Register the data-type number, *totype*, as castable from
data-type object, *descr*, of the given *scalar* kind. Use
*scalar* = :cdata:`NPY_NOSCALAR` to register that an array of data-type
*descr* can be cast safely to a data-type whose type_number is
*totype*.
Special functions for PyArray_OBJECT
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. cfunction:: int PyArray_INCREF(PyArrayObject* op)
Used for an array, *op*, that contains any Python objects. It
increments the reference count of every object in the array
according to the data-type of *op*. A -1 is returned if an error
occurs, otherwise 0 is returned.
.. cfunction:: void PyArray_Item_INCREF(char* ptr, PyArray_Descr* dtype)
A function to INCREF all the objects at the location *ptr*
according to the data-type *dtype*. If *ptr* is the start of a
record with an object at any offset, then this will (recursively)
increment the reference count of all object-like items in the
record.
.. cfunction:: int PyArray_XDECREF(PyArrayObject* op)
Used for an array, *op*, that contains any Python objects. It
decrements the reference count of every object in the array
according to the data-type of *op*. Normal return value is 0. A
-1 is returned if an error occurs.
.. cfunction:: void PyArray_Item_XDECREF(char* ptr, PyArray_Descr* dtype)
A function to XDECREF all the object-like items at the loacation
*ptr* as recorded in the data-type, *dtype*. This works
recursively so that if ``dtype`` itself has fields with data-types
that contain object-like items, all the object-like fields will be
XDECREF ``'d``.
.. cfunction:: void PyArray_FillObjectArray(PyArrayObject* arr, PyObject* obj)
Fill a newly created array with a single value obj at all
locations in the structure with object data-types. No checking is
performed but *arr* must be of data-type :ctype:`PyArray_OBJECT` and be
single-segment and uninitialized (no previous objects in
position). Use :cfunc:`PyArray_DECREF` (*arr*) if you need to
decrement all the items in the object array prior to calling this
function.
Array flags
-----------
The ``flags`` attribute of the ``PyArrayObject`` structure contains
important information about the memory used by the array (pointed to
by the data member) This flag information must be kept accurate or
strange results and even segfaults may result.
There are 6 (binary) flags that describe the memory area used by the
data buffer. These constants are defined in ``arrayobject.h`` and
determine the bit-position of the flag. Python exposes a nice
attribute- based interface as well as a dictionary-like interface for
getting (and, if appropriate, setting) these flags.
Memory areas of all kinds can be pointed to by an ndarray,
necessitating these flags. If you get an arbitrary ``PyArrayObject``
in C-code, you need to be aware of the flags that are set. If you
need to guarantee a certain kind of array (like ``NPY_CONTIGUOUS`` and
``NPY_BEHAVED``), then pass these requirements into the
PyArray_FromAny function.
Basic Array Flags
^^^^^^^^^^^^^^^^^
An ndarray can have a data segment that is not a simple contiguous
chunk of well-behaved memory you can manipulate. It may not be aligned
with word boundaries (very important on some platforms). It might have
its data in a different byte-order than the machine recognizes. It
might not be writeable. It might be in Fortan-contiguous order. The
array flags are used to indicate what can be said about data
associated with an array.
.. cvar:: NPY_C_CONTIGUOUS
The data area is in C-style contiguous order (last index varies the
fastest).
.. cvar:: NPY_F_CONTIGUOUS
The data area is in Fortran-style contiguous order (first index varies
the fastest).
Notice that contiguous 1-d arrays are always both ``NPY_FORTRAN``
contiguous and C contiguous. Both of these flags can be checked and
are convenience flags only as whether or not an array is
``NPY_CONTIGUOUS`` or ``NPY_FORTRAN`` can be determined by the
``strides``, ``dimensions``, and ``itemsize`` attributes.
.. cvar:: NPY_OWNDATA
The data area is owned by this array.
.. cvar:: NPY_ALIGNED
The data area is aligned appropriately (for all strides).
.. cvar:: NPY_WRITEABLE
The data area can be written to.
Notice that the above 3 flags are are defined so that a new, well-
behaved array has these flags defined as true.
.. cvar:: NPY_UPDATEIFCOPY
The data area represents a (well-behaved) copy whose information
should be transferred back to the original when this array is deleted.
This is a special flag that is set if this array represents a copy
made because a user required certain flags in
:cfunc:`PyArray_FromAny` and a copy had to be made of some other
array (and the user asked for this flag to be set in such a
situation). The base attribute then points to the "misbehaved"
array (which is set read_only). When the array with this flag set
is deallocated, it will copy its contents back to the "misbehaved"
array (casting if necessary) and will reset the "misbehaved" array
to :cdata:`NPY_WRITEABLE`. If the "misbehaved" array was not
:cdata:`NPY_WRITEABLE` to begin with then :cfunc:`PyArray_FromAny`
would have returned an error because :cdata:`NPY_UPDATEIFCOPY`
would not have been possible.
:cfunc:`PyArray_UpdateFlags` (obj, flags) will update the
``obj->flags`` for ``flags`` which can be any of
:cdata:`NPY_CONTIGUOUS`, :cdata:`NPY_FORTRAN`, :cdata:`NPY_ALIGNED`,
or :cdata:`NPY_WRITEABLE`.
Combinations of array flags
^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. cvar:: NPY_BEHAVED
:cdata:`NPY_ALIGNED` \| :cdata:`NPY_WRITEABLE`
.. cvar:: NPY_CARRAY
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_BEHAVED`
.. cvar:: NPY_CARRAY_RO
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_FARRAY
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_BEHAVED`
.. cvar:: NPY_FARRAY_RO
:cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
.. cvar:: NPY_DEFAULT
:cdata:`NPY_CARRAY`
.. cvar:: NPY_UPDATE_ALL
:cdata:`NPY_C_CONTIGUOUS` \| :cdata:`NPY_F_CONTIGUOUS` \| :cdata:`NPY_ALIGNED`
Flag-like constants
^^^^^^^^^^^^^^^^^^^
These constants are used in :cfunc:`PyArray_FromAny` (and its macro forms) to
specify desired properties of the new array.
.. cvar:: NPY_FORCECAST
Cast to the desired type, even if it can't be done without losing
information.
.. cvar:: NPY_ENSURECOPY
Make sure the resulting array is a copy of the original.
.. cvar:: NPY_ENSUREARRAY
Make sure the resulting object is an actual ndarray (or bigndarray),
and not a sub-class.
.. cvar:: NPY_NOTSWAPPED
Only used in :cfunc:`PyArray_CheckFromAny` to over-ride the byteorder
of the data-type object passed in.
.. cvar:: NPY_BEHAVED_NS
:cdata:`NPY_ALIGNED` \| :cdata:`NPY_WRITEABLE` \| :cdata:`NPY_NOTSWAPPED`
Flag checking
^^^^^^^^^^^^^
For all of these macros *arr* must be an instance of a (subclass of)
:cdata:`PyArray_Type`, but no checking is done.
.. cfunction:: PyArray_CHKFLAGS(arr, flags)
The first parameter, arr, must be an ndarray or subclass. The
parameter, *flags*, should be an integer consisting of bitwise
combinations of the possible flags an array can have:
:cdata:`NPY_C_CONTIGUOUS`, :cdata:`NPY_F_CONTIGUOUS`,
:cdata:`NPY_OWNDATA`, :cdata:`NPY_ALIGNED`,
:cdata:`NPY_WRITEABLE`, :cdata:`NPY_UPDATEIFCOPY`.
.. cfunction:: PyArray_ISCONTIGUOUS(arr)
Evaluates true if *arr* is C-style contiguous.
.. cfunction:: PyArray_ISFORTRAN(arr)
Evaluates true if *arr* is Fortran-style contiguous.
.. cfunction:: PyArray_ISWRITEABLE(arr)
Evaluates true if the data area of *arr* can be written to
.. cfunction:: PyArray_ISALIGNED(arr)
Evaluates true if the data area of *arr* is properly aligned on
the machine.
.. cfunction:: PyArray_ISBEHAVED(arr)
Evalutes true if the data area of *arr* is aligned and writeable
and in machine byte-order according to its descriptor.
.. cfunction:: PyArray_ISBEHAVED_RO(arr)
Evaluates true if the data area of *arr* is aligned and in machine
byte-order.
.. cfunction:: PyArray_ISCARRAY(arr)
Evaluates true if the data area of *arr* is C-style contiguous,
and :cfunc:`PyArray_ISBEHAVED` (*arr*) is true.
.. cfunction:: PyArray_ISFARRAY(arr)
Evaluates true if the data area of *arr* is Fortran-style
contiguous and :cfunc:`PyArray_ISBEHAVED` (*arr*) is true.
.. cfunction:: PyArray_ISCARRAY_RO(arr)
Evaluates true if the data area of *arr* is C-style contiguous,
aligned, and in machine byte-order.
.. cfunction:: PyArray_ISFARRAY_RO(arr)
Evaluates true if the data area of *arr* is Fortran-style
contiguous, aligned, and in machine byte-order **.**
.. cfunction:: PyArray_ISONESEGMENT(arr)
Evaluates true if the data area of *arr* consists of a single
(C-style or Fortran-style) contiguous segment.
.. cfunction:: void PyArray_UpdateFlags(PyArrayObject* arr, int flagmask)
The :cdata:`NPY_C_CONTIGUOUS`, :cdata:`NPY_ALIGNED`, and
:cdata:`NPY_F_CONTIGUOUS` array flags can be "calculated" from the
array object itself. This routine updates one or more of these
flags of *arr* as specified in *flagmask* by performing the
required calculation.
.. warning::
It is important to keep the flags updated (using
:cfunc:`PyArray_UpdateFlags` can help) whenever a manipulation with an
array is performed that might cause them to change. Later
calculations in NumPy that rely on the state of these flags do not
repeat the calculation to update them.
Array method alternative API
----------------------------
Conversion
^^^^^^^^^^
.. cfunction:: PyObject* PyArray_GetField(PyArrayObject* self, PyArray_Descr* dtype, int offset)
Equivalent to :meth:`ndarray.getfield` (*self*, *dtype*, *offset*). Return
a new array of the given *dtype* using the data in the current
array at a specified *offset* in bytes. The *offset* plus the
itemsize of the new array type must be less than *self*
->descr->elsize or an error is raised. The same shape and strides
as the original array are used. Therefore, this function has the
effect of returning a field from a record array. But, it can also
be used to select specific bytes or groups of bytes from any array
type.
.. cfunction:: int PyArray_SetField(PyArrayObject* self, PyArray_Descr* dtype, int offset, PyObject* val)
Equivalent to :meth:`ndarray.setfield` (*self*, *val*, *dtype*, *offset*
). Set the field starting at *offset* in bytes and of the given
*dtype* to *val*. The *offset* plus *dtype* ->elsize must be less
than *self* ->descr->elsize or an error is raised. Otherwise, the
*val* argument is converted to an array and copied into the field
pointed to. If necessary, the elements of *val* are repeated to
fill the destination array, But, the number of elements in the
destination must be an integer multiple of the number of elements
in *val*.
.. cfunction:: PyObject* PyArray_Byteswap(PyArrayObject* self, Bool inplace)
Equivalent to :meth:`ndarray.byteswap` (*self*, *inplace*). Return an array
whose data area is byteswapped. If *inplace* is non-zero, then do
the byteswap inplace and return a reference to self. Otherwise,
create a byteswapped copy and leave self unchanged.
.. cfunction:: PyObject* PyArray_NewCopy(PyArrayObject* old, NPY_ORDER order)
Equivalent to :meth:`ndarray.copy` (*self*, *fortran*). Make a copy of the
*old* array. The returned array is always aligned and writeable
with data interpreted the same as the old array. If *order* is
:cdata:`NPY_CORDER`, then a C-style contiguous array is returned. If
*order* is :cdata:`NPY_FORTRANORDER`, then a Fortran-style contiguous
array is returned. If *order is* :cdata:`NPY_ANYORDER`, then the array
returned is Fortran-style contiguous only if the old one is;
otherwise, it is C-style contiguous.
.. cfunction:: PyObject* PyArray_ToList(PyArrayObject* self)
Equivalent to :meth:`ndarray.tolist` (*self*). Return a nested Python list
from *self*.
.. cfunction:: PyObject* PyArray_ToString(PyArrayObject* self, NPY_ORDER order)
Equivalent to :meth:`ndarray.tostring` (*self*, *order*). Return the bytes
of this array in a Python string.
.. cfunction:: PyObject* PyArray_ToFile(PyArrayObject* self, FILE* fp, char* sep, char* format)
Write the contents of *self* to the file pointer *fp* in C-style
contiguous fashion. Write the data as binary bytes if *sep* is the
string ""or ``NULL``. Otherwise, write the contents of *self* as
text using the *sep* string as the item separator. Each item will
be printed to the file. If the *format* string is not ``NULL`` or
"", then it is a Python print statement format string showing how
the items are to be written.
.. cfunction:: int PyArray_Dump(PyObject* self, PyObject* file, int protocol)
Pickle the object in *self* to the given *file* (either a string
or a Python file object). If *file* is a Python string it is
considered to be the name of a file which is then opened in binary
mode. The given *protocol* is used (if *protocol* is negative, or
the highest available is used). This is a simple wrapper around
cPickle.dump(*self*, *file*, *protocol*).
.. cfunction:: PyObject* PyArray_Dumps(PyObject* self, int protocol)
Pickle the object in *self* to a Python string and return it. Use
the Pickle *protocol* provided (or the highest available if
*protocol* is negative).
.. cfunction:: int PyArray_FillWithScalar(PyArrayObject* arr, PyObject* obj)
Fill the array, *arr*, with the given scalar object, *obj*. The
object is first converted to the data type of *arr*, and then
copied into every location. A -1 is returned if an error occurs,
otherwise 0 is returned.
.. cfunction:: PyObject* PyArray_View(PyArrayObject* self, PyArray_Descr* dtype)
Equivalent to :meth:`ndarray.view` (*self*, *dtype*). Return a new view of
the array *self* as possibly a different data-type, *dtype*. If
*dtype* is ``NULL``, then the returned array will have the same
data type as *self*. The new data-type must be consistent with
the size of *self*. Either the itemsizes must be identical, or
*self* must be single-segment and the total number of bytes must
be the same. In the latter case the dimensions of the returned
array will be altered in the last (or first for Fortran-style
contiguous arrays) dimension. The data area of the returned array
and self is exactly the same.
Shape Manipulation
^^^^^^^^^^^^^^^^^^
.. cfunction:: PyObject* PyArray_Newshape(PyArrayObject* self, PyArray_Dims* newshape)
Result will be a new array (pointing to the same memory location
as *self* if possible), but having a shape given by *newshape*
. If the new shape is not compatible with the strides of *self*,
then a copy of the array with the new specified shape will be
returned.
.. cfunction:: PyObject* PyArray_Reshape(PyArrayObject* self, PyObject* shape)
Equivalent to :meth:`ndarray.reshape` (*self*, *shape*) where *shape* is a
sequence. Converts *shape* to a :ctype:`PyArray_Dims` structure and
calls :cfunc:`PyArray_Newshape` internally.
.. cfunction:: PyObject* PyArray_Squeeze(PyArrayObject* self)
Equivalent to :meth:`ndarray.squeeze` (*self*). Return a new view of *self*
with all of the dimensions of length 1 removed from the shape.
.. warning::
matrix objects are always 2-dimensional. Therefore,
:cfunc:`PyArray_Squeeze` has no effect on arrays of matrix sub-class.
.. cfunction:: PyObject* PyArray_SwapAxes(PyArrayObject* self, int a1, int a2)
Equivalent to :meth:`ndarray.swapaxes` (*self*, *a1*, *a2*). The returned
array is a new view of the data in *self* with the given axes,
*a1* and *a2*, swapped.
.. cfunction:: PyObject* PyArray_Resize(PyArrayObject* self, PyArray_Dims* newshape, int refcheck, NPY_ORDER fortran)
Equivalent to :meth:`ndarray.resize` (*self*, *newshape*, refcheck
``=`` *refcheck*, order= fortran ). This function only works on
single-segment arrays. It changes the shape of *self* inplace and
will reallocate the memory for *self* if *newshape* has a
different total number of elements then the old shape. If
reallocation is necessary, then *self* must own its data, have
*self* - ``>base==NULL``, have *self* - ``>weakrefs==NULL``, and
(unless refcheck is 0) not be referenced by any other array. A
reference to the new array is returned. The fortran argument can
be :cdata:`NPY_ANYORDER`, :cdata:`NPY_CORDER`, or
:cdata:`NPY_FORTRANORDER`. It currently has no effect. Eventually
it could be used to determine how the resize operation should view
the data when constructing a differently-dimensioned array.
.. cfunction:: PyObject* PyArray_Transpose(PyArrayObject* self, PyArray_Dims* permute)
Equivalent to :meth:`ndarray.transpose` (*self*, *permute*). Permute the
axes of the ndarray object *self* according to the data structure
*permute* and return the result. If *permute* is ``NULL``, then
the resulting array has its axes reversed. For example if *self*
has shape :math:`10\times20\times30`, and *permute* ``.ptr`` is
(0,2,1) the shape of the result is :math:`10\times30\times20.` If
*permute* is ``NULL``, the shape of the result is
:math:`30\times20\times10.`
.. cfunction:: PyObject* PyArray_Flatten(PyArrayObject* self, NPY_ORDER order)
Equivalent to :meth:`ndarray.flatten` (*self*, *order*). Return a 1-d copy
of the array. If *order* is :cdata:`NPY_FORTRANORDER` the elements are
scanned out in Fortran order (first-dimension varies the
fastest). If *order* is :cdata:`NPY_CORDER`, the elements of ``self``
are scanned in C-order (last dimension varies the fastest). If
*order* :cdata:`NPY_ANYORDER`, then the result of
:cfunc:`PyArray_ISFORTRAN` (*self*) is used to determine which order
to flatten.
.. cfunction:: PyObject* PyArray_Ravel(PyArrayObject* self, NPY_ORDER order)
Equivalent to *self*.ravel(*order*). Same basic functionality
as :cfunc:`PyArray_Flatten` (*self*, *order*) except if *order* is 0
and *self* is C-style contiguous, the shape is altered but no copy
is performed.
Item selection and manipulation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. cfunction:: PyObject* PyArray_TakeFrom(PyArrayObject* self, PyObject* indices, int axis, PyArrayObject* ret, NPY_CLIPMODE clipmode)
Equivalent to :meth:`ndarray.take` (*self*, *indices*, *axis*, *ret*,
*clipmode*) except *axis* =None in Python is obtained by setting
*axis* = :cdata:`NPY_MAXDIMS` in C. Extract the items from self
indicated by the integer-valued *indices* along the given *axis.*
The clipmode argument can be :cdata:`NPY_RAISE`, :cdata:`NPY_WRAP`, or
:cdata:`NPY_CLIP` to indicate what to do with out-of-bound indices. The
*ret* argument can specify an output array rather than having one
created internally.
.. cfunction:: PyObject* PyArray_PutTo(PyArrayObject* self, PyObject* values, PyObject* indices, NPY_CLIPMODE clipmode)
Equivalent to *self*.put(*values*, *indices*, *clipmode*
). Put *values* into *self* at the corresponding (flattened)
*indices*. If *values* is too small it will be repeated as
necessary.
.. cfunction:: PyObject* PyArray_PutMask(PyArrayObject* self, PyObject* values, PyObject* mask)
Place the *values* in *self* wherever corresponding positions
(using a flattened context) in *mask* are true. The *mask* and
*self* arrays must have the same total number of elements. If
*values* is too small, it will be repeated as necessary.
.. cfunction:: PyObject* PyArray_Repeat(PyArrayObject* self, PyObject* op, int axis)
Equivalent to :meth:`ndarray.repeat` (*self*, *op*, *axis*). Copy the
elements of *self*, *op* times along the given *axis*. Either
*op* is a scalar integer or a sequence of length *self*
->dimensions[ *axis* ] indicating how many times to repeat each
item along the axis.
.. cfunction:: PyObject* PyArray_Choose(PyArrayObject* self, PyObject* op, PyArrayObject* ret, NPY_CLIPMODE clipmode)
Equivalent to :meth:`ndarray.choose` (*self*, *op*, *ret*, *clipmode*).
Create a new array by selecting elements from the sequence of
arrays in *op* based on the integer values in *self*. The arrays
must all be broadcastable to the same shape and the entries in
*self* should be between 0 and len(*op*). The output is placed
in *ret* unless it is ``NULL`` in which case a new output is
created. The *clipmode* argument determines behavior for when
entries in *self* are not between 0 and len(*op*).
.. cvar:: NPY_RAISE
raise a ValueError;
.. cvar:: NPY_WRAP
wrap values < 0 by adding len(*op*) and values >=len(*op*)
by subtracting len(*op*) until they are in range;
.. cvar:: NPY_CLIP
all values are clipped to the region [0, len(*op*) ).
.. cfunction:: PyObject* PyArray_Sort(PyArrayObject* self, int axis)
Equivalent to :meth:`ndarray.sort` (*self*, *axis*). Return an array with
the items of *self* sorted along *axis*.
.. cfunction:: PyObject* PyArray_ArgSort(PyArrayObject* self, int axis)
Equivalent to :meth:`ndarray.argsort` (*self*, *axis*). Return an array of
indices such that selection of these indices along the given
``axis`` would return a sorted version of *self*. If *self*
->descr is a data-type with fields defined, then
self->descr->names is used to determine the sort order. A
comparison where the first field is equal will use the second
field and so on. To alter the sort order of a record array, create
a new data-type with a different order of names and construct a
view of the array with that new data-type.
.. cfunction:: PyObject* PyArray_LexSort(PyObject* sort_keys, int axis)
Given a sequence of arrays (*sort_keys*) of the same shape,
return an array of indices (similar to :cfunc:`PyArray_ArgSort` (...))
that would sort the arrays lexicographically. A lexicographic sort
specifies that when two keys are found to be equal, the order is
based on comparison of subsequent keys. A merge sort (which leaves
equal entries unmoved) is required to be defined for the
types. The sort is accomplished by sorting the indices first using
the first *sort_key* and then using the second *sort_key* and so
forth. This is equivalent to the lexsort(*sort_keys*, *axis*)
Python command. Because of the way the merge-sort works, be sure
to understand the order the *sort_keys* must be in (reversed from
the order you would use when comparing two elements).
If these arrays are all collected in a record array, then
:cfunc:`PyArray_Sort` (...) can also be used to sort the array
directly.
.. cfunction:: PyObject* PyArray_SearchSorted(PyArrayObject* self, PyObject* values)
Equivalent to :meth:`ndarray.searchsorted` (*self*, *values*). Assuming
*self* is a 1-d array in ascending order representing bin
boundaries then the output is an array the same shape as *values*
of bin numbers, giving the bin into which each item in *values*
would be placed. No checking is done on whether or not self is in
ascending order.
.. cfunction:: PyObject* PyArray_Diagonal(PyArrayObject* self, int offset, int axis1, int axis2)
Equivalent to :meth:`ndarray.diagonal` (*self*, *offset*, *axis1*, *axis2*
). Return the *offset* diagonals of the 2-d arrays defined by
*axis1* and *axis2*.
.. cfunction:: PyObject* PyArray_Nonzero(PyArrayObject* self)
Equivalent to :meth:`ndarray.nonzero` (*self*). Returns a tuple of index
arrays that select elements of *self* that are nonzero. If (nd=
:cfunc:`PyArray_NDIM` ( ``self`` ))==1, then a single index array is
returned. The index arrays have data type :cdata:`NPY_INTP`. If a
tuple is returned (nd :math:`\neq` 1), then its length is nd.
.. cfunction:: PyObject* PyArray_Compress(PyArrayObject* self, PyObject* condition, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.compress` (*self*, *condition*, *axis*
). Return the elements along *axis* corresponding to elements of
*condition* that are true.
Calculation
^^^^^^^^^^^
.. tip::
Pass in :cdata:`NPY_MAXDIMS` for axis in order to achieve the same
effect that is obtained by passing in *axis* = :const:`None` in Python
(treating the array as a 1-d array).
.. cfunction:: PyObject* PyArray_ArgMax(PyArrayObject* self, int axis)
Equivalent to :meth:`ndarray.argmax` (*self*, *axis*). Return the index of
the largest element of *self* along *axis*.
.. cfunction:: PyObject* PyArray_ArgMin(PyArrayObject* self, int axis)
Equivalent to :meth:`ndarray.argmin` (*self*, *axis*). Return the index of
the smallest element of *self* along *axis*.
.. cfunction:: PyObject* PyArray_Max(PyArrayObject* self, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.max` (*self*, *axis*). Return the largest
element of *self* along the given *axis*.
.. cfunction:: PyObject* PyArray_Min(PyArrayObject* self, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.min` (*self*, *axis*). Return the smallest
element of *self* along the given *axis*.
.. cfunction:: PyObject* PyArray_Ptp(PyArrayObject* self, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.ptp` (*self*, *axis*). Return the difference
between the largest element of *self* along *axis* and the
smallest element of *self* along *axis*.
.. note::
The rtype argument specifies the data-type the reduction should
take place over. This is important if the data-type of the array
is not "large" enough to handle the output. By default, all
integer data-types are made at least as large as :cdata:`NPY_LONG`
for the "add" and "multiply" ufuncs (which form the basis for
mean, sum, cumsum, prod, and cumprod functions).
.. cfunction:: PyObject* PyArray_Mean(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.mean` (*self*, *axis*, *rtype*). Returns the
mean of the elements along the given *axis*, using the enumerated
type *rtype* as the data type to sum in. Default sum behavior is
obtained using :cdata:`PyArray_NOTYPE` for *rtype*.
.. cfunction:: PyObject* PyArray_Trace(PyArrayObject* self, int offset, int axis1, int axis2, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.trace` (*self*, *offset*, *axis1*, *axis2*,
*rtype*). Return the sum (using *rtype* as the data type of
summation) over the *offset* diagonal elements of the 2-d arrays
defined by *axis1* and *axis2* variables. A positive offset
chooses diagonals above the main diagonal. A negative offset
selects diagonals below the main diagonal.
.. cfunction:: PyObject* PyArray_Clip(PyArrayObject* self, PyObject* min, PyObject* max)
Equivalent to :meth:`ndarray.clip` (*self*, *min*, *max*). Clip an array,
*self*, so that values larger than *max* are fixed to *max* and
values less than *min* are fixed to *min*.
.. cfunction:: PyObject* PyArray_Conjugate(PyArrayObject* self)
Equivalent to :meth:`ndarray.conjugate` (*self*).
Return the complex conjugate of *self*. If *self* is not of
complex data type, then return *self* with an reference.
.. cfunction:: PyObject* PyArray_Round(PyArrayObject* self, int decimals, PyArrayObject* out)
Equivalent to :meth:`ndarray.round` (*self*, *decimals*, *out*). Returns
the array with elements rounded to the nearest decimal place. The
decimal place is defined as the :math:`10^{-\textrm{decimals}}`
digit so that negative *decimals* cause rounding to the nearest 10's, 100's, etc. If out is ``NULL``, then the output array is created, otherwise the output is placed in *out* which must be the correct size and type.
.. cfunction:: PyObject* PyArray_Std(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.std` (*self*, *axis*, *rtype*). Return the
standard deviation using data along *axis* converted to data type
*rtype*.
.. cfunction:: PyObject* PyArray_Sum(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.sum` (*self*, *axis*, *rtype*). Return 1-d
vector sums of elements in *self* along *axis*. Perform the sum
after converting data to data type *rtype*.
.. cfunction:: PyObject* PyArray_CumSum(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.cumsum` (*self*, *axis*, *rtype*). Return
cumulative 1-d sums of elements in *self* along *axis*. Perform
the sum after converting data to data type *rtype*.
.. cfunction:: PyObject* PyArray_Prod(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.prod` (*self*, *axis*, *rtype*). Return 1-d
products of elements in *self* along *axis*. Perform the product
after converting data to data type *rtype*.
.. cfunction:: PyObject* PyArray_CumProd(PyArrayObject* self, int axis, int rtype, PyArrayObject* out)
Equivalent to :meth:`ndarray.cumprod` (*self*, *axis*, *rtype*). Return
1-d cumulative products of elements in ``self`` along ``axis``.
Perform the product after converting data to data type ``rtype``.
.. cfunction:: PyObject* PyArray_All(PyArrayObject* self, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.all` (*self*, *axis*). Return an array with
True elements for every 1-d sub-array of ``self`` defined by
``axis`` in which all the elements are True.
.. cfunction:: PyObject* PyArray_Any(PyArrayObject* self, int axis, PyArrayObject* out)
Equivalent to :meth:`ndarray.any` (*self*, *axis*). Return an array with
True elements for every 1-d sub-array of *self* defined by *axis*
in which any of the elements are True.
Functions
---------
Array Functions
^^^^^^^^^^^^^^^
.. cfunction:: int PyArray_AsCArray(PyObject** op, void* ptr, npy_intp* dims, int nd, int typenum, int itemsize)
Sometimes it is useful to access a multidimensional array as a
C-style multi-dimensional array so that algorithms can be
implemented using C's a[i][j][k] syntax. This routine returns a
pointer, *ptr*, that simulates this kind of C-style array, for
1-, 2-, and 3-d ndarrays.
:param op:
The address to any Python object. This Python object will be replaced
with an equivalent well-behaved, C-style contiguous, ndarray of the
given data type specifice by the last two arguments. Be sure that
stealing a reference in this way to the input object is justified.
:param ptr:
The address to a (ctype* for 1-d, ctype** for 2-d or ctype*** for 3-d)
variable where ctype is the equivalent C-type for the data type. On
return, *ptr* will be addressable as a 1-d, 2-d, or 3-d array.
:param dims:
An output array that contains the shape of the array object. This
array gives boundaries on any looping that will take place.
:param nd:
The dimensionality of the array (1, 2, or 3).
:param typenum:
The expected data type of the array.
:param itemsize:
This argument is only needed when *typenum* represents a
flexible array. Otherwise it should be 0.
.. note::
The simulation of a C-style array is not complete for 2-d and 3-d
arrays. For example, the simulated arrays of pointers cannot be passed
to subroutines expecting specific, statically-defined 2-d and 3-d
arrays. To pass to functions requiring those kind of inputs, you must
statically define the required array and copy data.
.. cfunction:: int PyArray_Free(PyObject* op, void* ptr)
Must be called with the same objects and memory locations returned
from :cfunc:`PyArray_AsCArray` (...). This function cleans up memory
that otherwise would get leaked.
.. cfunction:: PyObject* PyArray_Concatenate(PyObject* obj, int axis)
Join the sequence of objects in *obj* together along *axis* into a
single array. If the dimensions or types are not compatible an
error is raised.
.. cfunction:: PyObject* PyArray_InnerProduct(PyObject* obj1, PyObject* obj2)
Compute a product-sum over the last dimensions of *obj1* and
*obj2*. Neither array is conjugated.
.. cfunction:: PyObject* PyArray_MatrixProduct(PyObject* obj1, PyObject* obj)
Compute a product-sum over the last dimension of *obj1* and the
second-to-last dimension of *obj2*. For 2-d arrays this is a
matrix-product. Neither array is conjugated.
.. cfunction:: PyObject* PyArray_CopyAndTranspose(PyObject \* op)
A specialized copy and transpose function that works only for 2-d
arrays. The returned array is a transposed copy of *op*.
.. cfunction:: PyObject* PyArray_Correlate(PyObject* op1, PyObject* op2, int mode)
Compute the 1-d correlation of the 1-d arrays *op1* and *op2*
. The correlation is computed at each output point by multiplying
*op1* by a shifted version of *op2* and summing the result. As a
result of the shift, needed values outside of the defined range of
*op1* and *op2* are interpreted as zero. The mode determines how
many shifts to return: 0 - return only shifts that did not need to
assume zero- values; 1 - return an object that is the same size as
*op1*, 2 - return all possible shifts (any overlap at all is
accepted).
.. rubric:: Notes
This does not compute the usual correlation: if op2 is larger than op1, the
arguments are swapped, and the conjugate is never taken for complex arrays.
See PyArray_Correlate2 for the usual signal processing correlation.
.. cfunction:: PyObject* PyArray_Correlate2(PyObject* op1, PyObject* op2, int mode)
Updated version of PyArray_Correlate, which uses the usual definition of
correlation for 1d arrays. The correlation is computed at each output point
by multiplying *op1* by a shifted version of *op2* and summing the result.
As a result of the shift, needed values outside of the defined range of
*op1* and *op2* are interpreted as zero. The mode determines how many
shifts to return: 0 - return only shifts that did not need to assume zero-
values; 1 - return an object that is the same size as *op1*, 2 - return all
possible shifts (any overlap at all is accepted).
.. rubric:: Notes
Compute z as follows::
z[k] = sum_n op1[n] * conj(op2[n+k])
.. cfunction:: PyObject* PyArray_Where(PyObject* condition, PyObject* x, PyObject* y)
If both ``x`` and ``y`` are ``NULL``, then return
:cfunc:`PyArray_Nonzero` (*condition*). Otherwise, both *x* and *y*
must be given and the object returned is shaped like *condition*
and has elements of *x* and *y* where *condition* is respectively
True or False.
Other functions
^^^^^^^^^^^^^^^
.. cfunction:: Bool PyArray_CheckStrides(int elsize, int nd, npy_intp numbytes, npy_intp* dims, npy_intp* newstrides)
Determine if *newstrides* is a strides array consistent with the
memory of an *nd* -dimensional array with shape ``dims`` and
element-size, *elsize*. The *newstrides* array is checked to see
if jumping by the provided number of bytes in each direction will
ever mean jumping more than *numbytes* which is the assumed size
of the available memory segment. If *numbytes* is 0, then an
equivalent *numbytes* is computed assuming *nd*, *dims*, and
*elsize* refer to a single-segment array. Return :cdata:`NPY_TRUE` if
*newstrides* is acceptable, otherwise return :cdata:`NPY_FALSE`.
.. cfunction:: npy_intp PyArray_MultiplyList(npy_intp* seq, int n)
.. cfunction:: int PyArray_MultiplyIntList(int* seq, int n)
Both of these routines multiply an *n* -length array, *seq*, of
integers and return the result. No overflow checking is performed.
.. cfunction:: int PyArray_CompareLists(npy_intp* l1, npy_intp* l2, int n)
Given two *n* -length arrays of integers, *l1*, and *l2*, return
1 if the lists are identical; otherwise, return 0.
Array Iterators
---------------
An array iterator is a simple way to access the elements of an
N-dimensional array quickly and efficiently. Section `2
<#sec-array-iterator>`__ provides more description and examples of
this useful approach to looping over an array.
.. cfunction:: PyObject* PyArray_IterNew(PyObject* arr)
Return an array iterator object from the array, *arr*. This is
equivalent to *arr*. **flat**. The array iterator object makes
it easy to loop over an N-dimensional non-contiguous array in
C-style contiguous fashion.
.. cfunction:: PyObject* PyArray_IterAllButAxis(PyObject* arr, int \*axis)
Return an array iterator that will iterate over all axes but the
one provided in *\*axis*. The returned iterator cannot be used
with :cfunc:`PyArray_ITER_GOTO1D`. This iterator could be used to
write something similar to what ufuncs do wherein the loop over
the largest axis is done by a separate sub-routine. If *\*axis* is
negative then *\*axis* will be set to the axis having the smallest
stride and that axis will be used.
.. cfunction:: PyObject *PyArray_BroadcastToShape(PyObject* arr, npy_intp *dimensions, int nd)
Return an array iterator that is broadcast to iterate as an array
of the shape provided by *dimensions* and *nd*.
.. cfunction:: int PyArrayIter_Check(PyObject* op)
Evaluates true if *op* is an array iterator (or instance of a
subclass of the array iterator type).
.. cfunction:: void PyArray_ITER_RESET(PyObject* iterator)
Reset an *iterator* to the beginning of the array.
.. cfunction:: void PyArray_ITER_NEXT(PyObject* iterator)
Incremement the index and the dataptr members of the *iterator* to
point to the next element of the array. If the array is not
(C-style) contiguous, also increment the N-dimensional coordinates
array.
.. cfunction:: void *PyArray_ITER_DATA(PyObject* iterator)
A pointer to the current element of the array.
.. cfunction:: void PyArray_ITER_GOTO(PyObject* iterator, npy_intp* destination)
Set the *iterator* index, dataptr, and coordinates members to the
location in the array indicated by the N-dimensional c-array,
*destination*, which must have size at least *iterator*
->nd_m1+1.
.. cfunction:: PyArray_ITER_GOTO1D(PyObject* iterator, npy_intp index)
Set the *iterator* index and dataptr to the location in the array
indicated by the integer *index* which points to an element in the
C-styled flattened array.
.. cfunction:: int PyArray_ITER_NOTDONE(PyObject* iterator)
Evaluates TRUE as long as the iterator has not looped through all of
the elements, otherwise it evaluates FALSE.
Broadcasting (multi-iterators)
------------------------------
.. cfunction:: PyObject* PyArray_MultiIterNew(int num, ...)
A simplified interface to broadcasting. This function takes the
number of arrays to broadcast and then *num* extra ( :ctype:`PyObject *`
) arguments. These arguments are converted to arrays and iterators
are created. :cfunc:`PyArray_Broadcast` is then called on the resulting
multi-iterator object. The resulting, broadcasted mult-iterator
object is then returned. A broadcasted operation can then be
performed using a single loop and using :cfunc:`PyArray_MultiIter_NEXT`
(..)
.. cfunction:: void PyArray_MultiIter_RESET(PyObject* multi)
Reset all the iterators to the beginning in a multi-iterator
object, *multi*.
.. cfunction:: void PyArray_MultiIter_NEXT(PyObject* multi)
Advance each iterator in a multi-iterator object, *multi*, to its
next (broadcasted) element.
.. cfunction:: void *PyArray_MultiIter_DATA(PyObject* multi, int i)
Return the data-pointer of the *i* :math:`^{\textrm{th}}` iterator
in a multi-iterator object.
.. cfunction:: void PyArray_MultiIter_NEXTi(PyObject* multi, int i)
Advance the pointer of only the *i* :math:`^{\textrm{th}}` iterator.
.. cfunction:: void PyArray_MultiIter_GOTO(PyObject* multi, npy_intp* destination)
Advance each iterator in a multi-iterator object, *multi*, to the
given :math:`N` -dimensional *destination* where :math:`N` is the
number of dimensions in the broadcasted array.
.. cfunction:: void PyArray_MultiIter_GOTO1D(PyObject* multi, npy_intp index)
Advance each iterator in a multi-iterator object, *multi*, to the
corresponding location of the *index* into the flattened
broadcasted array.
.. cfunction:: int PyArray_MultiIter_NOTDONE(PyObject* multi)
Evaluates TRUE as long as the multi-iterator has not looped
through all of the elements (of the broadcasted result), otherwise
it evaluates FALSE.
.. cfunction:: int PyArray_Broadcast(PyArrayMultiIterObject* mit)
This function encapsulates the broadcasting rules. The *mit*
container should already contain iterators for all the arrays that
need to be broadcast. On return, these iterators will be adjusted
so that iteration over each simultaneously will accomplish the
broadcasting. A negative number is returned if an error occurs.
.. cfunction:: int PyArray_RemoveSmallest(PyArrayMultiIterObject* mit)
This function takes a multi-iterator object that has been
previously "broadcasted," finds the dimension with the smallest
"sum of strides" in the broadcasted result and adapts all the
iterators so as not to iterate over that dimension (by effectively
making them of length-1 in that dimension). The corresponding
dimension is returned unless *mit* ->nd is 0, then -1 is
returned. This function is useful for constructing ufunc-like
routines that broadcast their inputs correctly and then call a
strided 1-d version of the routine as the inner-loop. This 1-d
version is usually optimized for speed and for this reason the
loop should be performed over the axis that won't require large
stride jumps.
Neighborhood iterator
---------------------
.. versionadded:: 1.4.0
Neighborhood iterators are subclasses of the iterator object, and can be used
to iter over a neighborhood of a point. For example, you may want to iterate
over every voxel of a 3d image, and for every such voxel, iterate over an
hypercube. Neighborhood iterator automatically handle boundaries, thus making
this kind of code much easier to write than manual boundaries handling, at the
cost of a slight overhead.
.. cfunction:: PyObject* PyArray_NeighborhoodIterNew(PyArrayIterObject* iter, npy_intp bounds, int mode, PyArrayObject* fill_value)
This function creates a new neighborhood iterator from an existing
iterator. The neighborhood will be computed relatively to the position
currently pointed by *iter*, the bounds define the shape of the
neighborhood iterator, and the mode argument the boundaries handling mode.
The *bounds* argument is expected to be a (2 * iter->ao->nd) arrays, such
as the range bound[2*i]->bounds[2*i+1] defines the range where to walk for
dimension i (both bounds are included in the walked coordinates). The
bounds should be ordered for each dimension (bounds[2*i] <= bounds[2*i+1]).
The mode should be one of:
* NPY_NEIGHBORHOOD_ITER_ZERO_PADDING: zero padding. Outside bounds values
will be 0.
* NPY_NEIGHBORHOOD_ITER_ONE_PADDING: one padding, Outside bounds values
will be 1.
* NPY_NEIGHBORHOOD_ITER_CONSTANT_PADDING: constant padding. Outside bounds
values will be the same as the first item in fill_value.
* NPY_NEIGHBORHOOD_ITER_MIRROR_PADDING: mirror padding. Outside bounds
values will be as if the array items were mirrored. For example, for the
array [1, 2, 3, 4], x[-2] will be 2, x[-2] will be 1, x[4] will be 4,
x[5] will be 1, etc...
* NPY_NEIGHBORHOOD_ITER_CIRCULAR_PADDING: circular padding. Outside bounds
values will be as if the array was repeated. For example, for the
array [1, 2, 3, 4], x[-2] will be 3, x[-2] will be 4, x[4] will be 1,
x[5] will be 2, etc...
If the mode is constant filling (NPY_NEIGHBORHOOD_ITER_CONSTANT_PADDING),
fill_value should point to an array object which holds the filling value
(the first item will be the filling value if the array contains more than
one item). For other cases, fill_value may be NULL.
- The iterator holds a reference to iter
- Return NULL on failure (in which case the reference count of iter is not
changed)
- iter itself can be a Neighborhood iterator: this can be useful for .e.g
automatic boundaries handling
- the object returned by this function should be safe to use as a normal
iterator
- If the position of iter is changed, any subsequent call to
PyArrayNeighborhoodIter_Next is undefined behavior, and
PyArrayNeighborhoodIter_Reset must be called.
.. code-block:: c
PyArrayIterObject \*iter;
PyArrayNeighborhoodIterObject \*neigh_iter;
iter = PyArray_IterNew(x);
//For a 3x3 kernel
bounds = {-1, 1, -1, 1};
neigh_iter = (PyArrayNeighborhoodIterObject*)PyArrayNeighborhoodIter_New(
iter, bounds, NPY_NEIGHBORHOOD_ITER_ZERO_PADDING, NULL);
for(i = 0; i < iter->size; ++i) {
for (j = 0; j < neigh_iter->size; ++j) {
// Walk around the item currently pointed by iter->dataptr
PyArrayNeighborhoodIter_Next(neigh_iter);
}
// Move to the next point of iter
PyArrayIter_Next(iter);
PyArrayNeighborhoodIter_Reset(neigh_iter);
}
.. cfunction:: int PyArrayNeighborhoodIter_Reset(PyArrayNeighborhoodIterObject* iter)
Reset the iterator position to the first point of the neighborhood. This
should be called whenever the iter argument given at
PyArray_NeighborhoodIterObject is changed (see example)
.. cfunction:: int PyArrayNeighborhoodIter_Next(PyArrayNeighborhoodIterObject* iter)
After this call, iter->dataptr points to the next point of the
neighborhood. Calling this function after every point of the
neighborhood has been visited is undefined.
Array Scalars
-------------
.. cfunction:: PyObject* PyArray_Return(PyArrayObject* arr)
This function checks to see if *arr* is a 0-dimensional array and,
if so, returns the appropriate array scalar. It should be used
whenever 0-dimensional arrays could be returned to Python.
.. cfunction:: PyObject* PyArray_Scalar(void* data, PyArray_Descr* dtype, PyObject* itemsize)
Return an array scalar object of the given enumerated *typenum*
and *itemsize* by **copying** from memory pointed to by *data*
. If *swap* is nonzero then this function will byteswap the data
if appropriate to the data-type because array scalars are always
in correct machine-byte order.
.. cfunction:: PyObject* PyArray_ToScalar(void* data, PyArrayObject* arr)
Return an array scalar object of the type and itemsize indicated
by the array object *arr* copied from the memory pointed to by
*data* and swapping if the data in *arr* is not in machine
byte-order.
.. cfunction:: PyObject* PyArray_FromScalar(PyObject* scalar, PyArray_Descr* outcode)
Return a 0-dimensional array of type determined by *outcode* from
*scalar* which should be an array-scalar object. If *outcode* is
NULL, then the type is determined from *scalar*.
.. cfunction:: void PyArray_ScalarAsCtype(PyObject* scalar, void* ctypeptr)
Return in *ctypeptr* a pointer to the actual value in an array
scalar. There is no error checking so *scalar* must be an
array-scalar object, and ctypeptr must have enough space to hold
the correct type. For flexible-sized types, a pointer to the data
is copied into the memory of *ctypeptr*, for all other types, the
actual data is copied into the address pointed to by *ctypeptr*.
.. cfunction:: void PyArray_CastScalarToCtype(PyObject* scalar, void* ctypeptr, PyArray_Descr* outcode)
Return the data (cast to the data type indicated by *outcode*)
from the array-scalar, *scalar*, into the memory pointed to by
*ctypeptr* (which must be large enough to handle the incoming
memory).
.. cfunction:: PyObject* PyArray_TypeObjectFromType(int type)
Returns a scalar type-object from a type-number, *type*
. Equivalent to :cfunc:`PyArray_DescrFromType` (*type*)->typeobj
except for reference counting and error-checking. Returns a new
reference to the typeobject on success or ``NULL`` on failure.
.. cfunction:: NPY_SCALARKIND PyArray_ScalarKind(int typenum, PyArrayObject** arr)
Return the kind of scalar represented by *typenum* and the array
in *\*arr* (if *arr* is not ``NULL`` ). The array is assumed to be
rank-0 and only used if *typenum* represents a signed integer. If
*arr* is not ``NULL`` and the first element is negative then
:cdata:`NPY_INTNEG_SCALAR` is returned, otherwise
:cdata:`NPY_INTPOS_SCALAR` is returned. The possible return values
are :cdata:`NPY_{kind}_SCALAR` where ``{kind}`` can be **INTPOS**,
**INTNEG**, **FLOAT**, **COMPLEX**, **BOOL**, or **OBJECT**.
:cdata:`NPY_NOSCALAR` is also an enumerated value
:ctype:`NPY_SCALARKIND` variables can take on.
.. cfunction:: int PyArray_CanCoerceScalar(char thistype, char neededtype, NPY_SCALARKIND scalar)
Implements the rules for scalar coercion. Scalars are only
silently coerced from thistype to neededtype if this function
returns nonzero. If scalar is :cdata:`NPY_NOSCALAR`, then this
function is equivalent to :cfunc:`PyArray_CanCastSafely`. The rule is
that scalars of the same KIND can be coerced into arrays of the
same KIND. This rule means that high-precision scalars will never
cause low-precision arrays of the same KIND to be upcast.
Data-type descriptors
---------------------
.. warning::
Data-type objects must be reference counted so be aware of the
action on the data-type reference of different C-API calls. The
standard rule is that when a data-type object is returned it is a
new reference. Functions that take :ctype:`PyArray_Descr *` objects and
return arrays steal references to the data-type their inputs
unless otherwise noted. Therefore, you must own a reference to any
data-type object used as input to such a function.
.. cfunction:: int PyArrayDescr_Check(PyObject* obj)
Evaluates as true if *obj* is a data-type object ( :ctype:`PyArray_Descr *` ).
.. cfunction:: PyArray_Descr* PyArray_DescrNew(PyArray_Descr* obj)
Return a new data-type object copied from *obj* (the fields
reference is just updated so that the new object points to the
same fields dictionary if any).
.. cfunction:: PyArray_Descr* PyArray_DescrNewFromType(int typenum)
Create a new data-type object from the built-in (or
user-registered) data-type indicated by *typenum*. All builtin
types should not have any of their fields changed. This creates a
new copy of the :ctype:`PyArray_Descr` structure so that you can fill
it in as appropriate. This function is especially needed for
flexible data-types which need to have a new elsize member in
order to be meaningful in array construction.
.. cfunction:: PyArray_Descr* PyArray_DescrNewByteorder(PyArray_Descr* obj, char newendian)
Create a new data-type object with the byteorder set according to
*newendian*. All referenced data-type objects (in subdescr and
fields members of the data-type object) are also changed
(recursively). If a byteorder of :cdata:`NPY_IGNORE` is encountered it
is left alone. If newendian is :cdata:`NPY_SWAP`, then all byte-orders
are swapped. Other valid newendian values are :cdata:`NPY_NATIVE`,
:cdata:`NPY_LITTLE`, and :cdata:`NPY_BIG` which all cause the returned
data-typed descriptor (and all it's
referenced data-type descriptors) to have the corresponding byte-
order.
.. cfunction:: PyArray_Descr* PyArray_DescrFromObject(PyObject* op, PyArray_Descr* mintype)
Determine an appropriate data-type object from the object *op*
(which should be a "nested" sequence object) and the minimum
data-type descriptor mintype (which can be ``NULL`` ). Similar in
behavior to array(*op*).dtype. Don't confuse this function with
:cfunc:`PyArray_DescrConverter`. This function essentially looks at
all the objects in the (nested) sequence and determines the
data-type from the elements it finds.
.. cfunction:: PyArray_Descr* PyArray_DescrFromScalar(PyObject* scalar)
Return a data-type object from an array-scalar object. No checking
is done to be sure that *scalar* is an array scalar. If no
suitable data-type can be determined, then a data-type of
:cdata:`NPY_OBJECT` is returned by default.
.. cfunction:: PyArray_Descr* PyArray_DescrFromType(int typenum)
Returns a data-type object corresponding to *typenum*. The
*typenum* can be one of the enumerated types, a character code for
one of the enumerated types, or a user-defined type.
.. cfunction:: int PyArray_DescrConverter(PyObject* obj, PyArray_Descr** dtype)
Convert any compatible Python object, *obj*, to a data-type object
in *dtype*. A large number of Python objects can be converted to
data-type objects. See :ref:`arrays.dtypes` for a complete
description. This version of the converter converts None objects
to a :cdata:`NPY_DEFAULT_TYPE` data-type object. This function can
be used with the "O&" character code in :cfunc:`PyArg_ParseTuple`
processing.
.. cfunction:: int PyArray_DescrConverter2(PyObject* obj, PyArray_Descr** dtype)
Convert any compatible Python object, *obj*, to a data-type
object in *dtype*. This version of the converter converts None
objects so that the returned data-type is ``NULL``. This function
can also be used with the "O&" character in PyArg_ParseTuple
processing.
.. cfunction:: int Pyarray_DescrAlignConverter(PyObject* obj, PyArray_Descr** dtype)
Like :cfunc:`PyArray_DescrConverter` except it aligns C-struct-like
objects on word-boundaries as the compiler would.
.. cfunction:: int Pyarray_DescrAlignConverter2(PyObject* obj, PyArray_Descr** dtype)
Like :cfunc:`PyArray_DescrConverter2` except it aligns C-struct-like
objects on word-boundaries as the compiler would.
.. cfunction:: PyObject *PyArray_FieldNames(PyObject* dict)
Take the fields dictionary, *dict*, such as the one attached to a
data-type object and construct an ordered-list of field names such
as is stored in the names field of the :ctype:`PyArray_Descr` object.
Conversion Utilities
--------------------
For use with :cfunc:`PyArg_ParseTuple`
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All of these functions can be used in :cfunc:`PyArg_ParseTuple` (...) with
the "O&" format specifier to automatically convert any Python object
to the required C-object. All of these functions return
:cdata:`NPY_SUCCEED` if successful and :cdata:`NPY_FAIL` if not. The first
argument to all of these function is a Python object. The second
argument is the **address** of the C-type to convert the Python object
to.
.. warning::
Be sure to understand what steps you should take to manage the
memory when using these conversion functions. These functions can
require freeing memory, and/or altering the reference counts of
specific objects based on your use.
.. cfunction:: int PyArray_Converter(PyObject* obj, PyObject** address)
Convert any Python object to a :ctype:`PyArrayObject`. If
:cfunc:`PyArray_Check` (*obj*) is TRUE then its reference count is
incremented and a reference placed in *address*. If *obj* is not
an array, then convert it to an array using :cfunc:`PyArray_FromAny`
. No matter what is returned, you must DECREF the object returned
by this routine in *address* when you are done with it.
.. cfunction:: int PyArray_OutputConverter(PyObject* obj, PyArrayObject** address)
This is a default converter for output arrays given to
functions. If *obj* is :cdata:`Py_None` or ``NULL``, then *\*address*
will be ``NULL`` but the call will succeed. If :cfunc:`PyArray_Check` (
*obj*) is TRUE then it is returned in *\*address* without
incrementing its reference count.
.. cfunction:: int PyArray_IntpConverter(PyObject* obj, PyArray_Dims* seq)
Convert any Python sequence, *obj*, smaller than :cdata:`NPY_MAXDIMS`
to a C-array of :ctype:`npy_intp`. The Python object could also be a
single number. The *seq* variable is a pointer to a structure with
members ptr and len. On successful return, *seq* ->ptr contains a
pointer to memory that must be freed to avoid a memory leak. The
restriction on memory size allows this converter to be
conveniently used for sequences intended to be interpreted as
array shapes.
.. cfunction:: int PyArray_BufferConverter(PyObject* obj, PyArray_Chunk* buf)
Convert any Python object, *obj*, with a (single-segment) buffer
interface to a variable with members that detail the object's use
of its chunk of memory. The *buf* variable is a pointer to a
structure with base, ptr, len, and flags members. The
:ctype:`PyArray_Chunk` structure is binary compatibile with the
Python's buffer object (through its len member on 32-bit platforms
and its ptr member on 64-bit platforms or in Python 2.5). On
return, the base member is set to *obj* (or its base if *obj* is
already a buffer object pointing to another object). If you need
to hold on to the memory be sure to INCREF the base member. The
chunk of memory is pointed to by *buf* ->ptr member and has length
*buf* ->len. The flags member of *buf* is :cdata:`NPY_BEHAVED_RO` with
the :cdata:`NPY_WRITEABLE` flag set if *obj* has a writeable buffer
interface.
.. cfunction:: int PyArray_AxisConverter(PyObject \* obj, int* axis)
Convert a Python object, *obj*, representing an axis argument to
the proper value for passing to the functions that take an integer
axis. Specifically, if *obj* is None, *axis* is set to
:cdata:`NPY_MAXDIMS` which is interpreted correctly by the C-API
functions that take axis arguments.
.. cfunction:: int PyArray_BoolConverter(PyObject* obj, Bool* value)
Convert any Python object, *obj*, to :cdata:`NPY_TRUE` or
:cdata:`NPY_FALSE`, and place the result in *value*.
.. cfunction:: int PyArray_ByteorderConverter(PyObject* obj, char* endian)
Convert Python strings into the corresponding byte-order
character:
'>', '<', 's', '=', or '\|'.
.. cfunction:: int PyArray_SortkindConverter(PyObject* obj, NPY_SORTKIND* sort)
Convert Python strings into one of :cdata:`NPY_QUICKSORT` (starts
with 'q' or 'Q') , :cdata:`NPY_HEAPSORT` (starts with 'h' or 'H'),
or :cdata:`NPY_MERGESORT` (starts with 'm' or 'M').
.. cfunction:: int PyArray_SearchsideConverter(PyObject* obj, NPY_SEARCHSIDE* side)
Convert Python strings into one of :cdata:`NPY_SEARCHLEFT` (starts with 'l'
or 'L'), or :cdata:`NPY_SEARCHRIGHT` (starts with 'r' or 'R').
Other conversions
^^^^^^^^^^^^^^^^^
.. cfunction:: int PyArray_PyIntAsInt(PyObject* op)
Convert all kinds of Python objects (including arrays and array
scalars) to a standard integer. On error, -1 is returned and an
exception set. You may find useful the macro:
.. code-block:: c
#define error_converting(x) (((x) == -1) && PyErr_Occurred()
.. cfunction:: npy_intp PyArray_PyIntAsIntp(PyObject* op)
Convert all kinds of Python objects (including arrays and array
scalars) to a (platform-pointer-sized) integer. On error, -1 is
returned and an exception set.
.. cfunction:: int PyArray_IntpFromSequence(PyObject* seq, npy_intp* vals, int maxvals)
Convert any Python sequence (or single Python number) passed in as
*seq* to (up to) *maxvals* pointer-sized integers and place them
in the *vals* array. The sequence can be smaller then *maxvals* as
the number of converted objects is returned.
.. cfunction:: int PyArray_TypestrConvert(int itemsize, int gentype)
Convert typestring characters (with *itemsize*) to basic
enumerated data types. The typestring character corresponding to
signed and unsigned integers, floating point numbers, and
complex-floating point numbers are recognized and converted. Other
values of gentype are returned. This function can be used to
convert, for example, the string 'f4' to :cdata:`NPY_FLOAT32`.
Miscellaneous
-------------
Importing the API
^^^^^^^^^^^^^^^^^
In order to make use of the C-API from another extension module, the
``import_array`` () command must be used. If the extension module is
self-contained in a single .c file, then that is all that needs to be
done. If, however, the extension module involves multiple files where
the C-API is needed then some additional steps must be taken.
.. cfunction:: void import_array(void)
This function must be called in the initialization section of a
module that will make use of the C-API. It imports the module
where the function-pointer table is stored and points the correct
variable to it.
.. cmacro:: PY_ARRAY_UNIQUE_SYMBOL
.. cmacro:: NO_IMPORT_ARRAY
Using these #defines you can use the C-API in multiple files for a
single extension module. In each file you must define
:cmacro:`PY_ARRAY_UNIQUE_SYMBOL` to some name that will hold the
C-API (*e.g.* myextension_ARRAY_API). This must be done **before**
including the numpy/arrayobject.h file. In the module
intialization routine you call ``import_array`` (). In addition,
in the files that do not have the module initialization
sub_routine define :cmacro:`NO_IMPORT_ARRAY` prior to including
numpy/arrayobject.h.
Suppose I have two files coolmodule.c and coolhelper.c which need
to be compiled and linked into a single extension module. Suppose
coolmodule.c contains the required initcool module initialization
function (with the import_array() function called). Then,
coolmodule.c would have at the top:
.. code-block:: c
#define PY_ARRAY_UNIQUE_SYMBOL cool_ARRAY_API
#include numpy/arrayobject.h
On the other hand, coolhelper.c would contain at the top:
.. code-block:: c
#define PY_ARRAY_UNIQUE_SYMBOL cool_ARRAY_API
#define NO_IMPORT_ARRAY
#include numpy/arrayobject.h
Checking the API Version
^^^^^^^^^^^^^^^^^^^^^^^^
Because python extensions are not used in the same way as usual libraries on
most platforms, some errors cannot be automatically detected at build time or
even runtime. For example, if you build an extension using a function available
only for numpy >= 1.3.0, and you import the extension later with numpy 1.2, you
will not get an import error (but almost certainly a segmentation fault when
calling the function). That's why several functions are provided to check for
numpy versions. The macros :cdata:`NPY_VERSION` and
:cdata:`NPY_FEATURE_VERSION` corresponds to the numpy version used to build the
extension, whereas the versions returned by the functions
PyArray_GetNDArrayCVersion and PyArray_GetNDArrayCFeatureVersion corresponds to
the runtime numpy's version.
The rules for ABI and API compatibilities can be summarized as follows:
* Whenever :cdata:`NPY_VERSION` != PyArray_GetNDArrayCVersion, the
extension has to be recompiled (ABI incompatibility).
* :cdata:`NPY_VERSION` == PyArray_GetNDArrayCVersion and
:cdata:`NPY_FEATURE_VERSION` <= PyArray_GetNDArrayCFeatureVersion means
backward compatible changes.
ABI incompatibility is automatically detected in every numpy's version. API
incompatibility detection was added in numpy 1.4.0. If you want to supported
many different numpy versions with one extension binary, you have to build your
extension with the lowest NPY_FEATURE_VERSION as possible.
.. cfunction:: unsigned int PyArray_GetNDArrayCVersion(void)
This just returns the value :cdata:`NPY_VERSION`. :cdata:`NPY_VERSION`
changes whenever a backward incompatible change at the ABI level. Because
it is in the C-API, however, comparing the output of this function from the
value defined in the current header gives a way to test if the C-API has
changed thus requiring a re-compilation of extension modules that use the
C-API. This is automatically checked in the function import_array.
.. cfunction:: unsigned int PyArray_GetNDArrayCFeatureVersion(void)
.. versionadded:: 1.4.0
This just returns the value :cdata:`NPY_FEATURE_VERSION`.
:cdata:`NPY_FEATURE_VERSION` changes whenever the API changes (e.g. a
function is added). A changed value does not always require a recompile.
Internal Flexibility
^^^^^^^^^^^^^^^^^^^^
.. cfunction:: int PyArray_SetNumericOps(PyObject* dict)
NumPy stores an internal table of Python callable objects that are
used to implement arithmetic operations for arrays as well as
certain array calculation methods. This function allows the user
to replace any or all of these Python objects with their own
versions. The keys of the dictionary, *dict*, are the named
functions to replace and the paired value is the Python callable
object to use. Care should be taken that the function used to
replace an internal array operation does not itself call back to
that internal array operation (unless you have designed the
function to handle that), or an unchecked infinite recursion can
result (possibly causing program crash). The key names that
represent operations that can be replaced are:
**add**, **subtract**, **multiply**, **divide**,
**remainder**, **power**, **square**, **reciprocal**,
**ones_like**, **sqrt**, **negative**, **absolute**,
**invert**, **left_shift**, **right_shift**,
**bitwise_and**, **bitwise_xor**, **bitwise_or**,
**less**, **less_equal**, **equal**, **not_equal**,
**greater**, **greater_equal**, **floor_divide**,
**true_divide**, **logical_or**, **logical_and**,
**floor**, **ceil**, **maximum**, **minimum**, **rint**.
These functions are included here because they are used at least once
in the array object's methods. The function returns -1 (without
setting a Python Error) if one of the objects being assigned is not
callable.
.. cfunction:: PyObject* PyArray_GetNumericOps(void)
Return a Python dictionary containing the callable Python objects
stored in the the internal arithmetic operation table. The keys of
this dictionary are given in the explanation for :cfunc:`PyArray_SetNumericOps`.
.. cfunction:: void PyArray_SetStringFunction(PyObject* op, int repr)
This function allows you to alter the tp_str and tp_repr methods
of the array object to any Python function. Thus you can alter
what happens for all arrays when str(arr) or repr(arr) is called
from Python. The function to be called is passed in as *op*. If
*repr* is non-zero, then this function will be called in response
to repr(arr), otherwise the function will be called in response to
str(arr). No check on whether or not *op* is callable is
performed. The callable passed in to *op* should expect an array
argument and should return a string to be printed.
Memory management
^^^^^^^^^^^^^^^^^
.. cfunction:: char* PyDataMem_NEW(size_t nbytes)
.. cfunction:: PyDataMem_FREE(char* ptr)
.. cfunction:: char* PyDataMem_RENEW(void * ptr, size_t newbytes)
Macros to allocate, free, and reallocate memory. These macros are used
internally to create arrays.
.. cfunction:: npy_intp* PyDimMem_NEW(nd)
.. cfunction:: PyDimMem_FREE(npy_intp* ptr)
.. cfunction:: npy_intp* PyDimMem_RENEW(npy_intp* ptr, npy_intp newnd)
Macros to allocate, free, and reallocate dimension and strides memory.
.. cfunction:: PyArray_malloc(nbytes)
.. cfunction:: PyArray_free(ptr)
.. cfunction:: PyArray_realloc(ptr, nbytes)
These macros use different memory allocators, depending on the
constant :cdata:`NPY_USE_PYMEM`. The system malloc is used when
:cdata:`NPY_USE_PYMEM` is 0, if :cdata:`NPY_USE_PYMEM` is 1, then
the Python memory allocator is used.
Threading support
^^^^^^^^^^^^^^^^^
These macros are only meaningful if :cdata:`NPY_ALLOW_THREADS`
evaluates True during compilation of the extension module. Otherwise,
these macros are equivalent to whitespace. Python uses a single Global
Interpreter Lock (GIL) for each Python process so that only a single
thread may excecute at a time (even on multi-cpu machines). When
calling out to a compiled function that may take time to compute (and
does not have side-effects for other threads like updated global
variables), the GIL should be released so that other Python threads
can run while the time-consuming calculations are performed. This can
be accomplished using two groups of macros. Typically, if one macro in
a group is used in a code block, all of them must be used in the same
code block. Currently, :cdata:`NPY_ALLOW_THREADS` is defined to the
python-defined :cdata:`WITH_THREADS` constant unless the environment
variable :cdata:`NPY_NOSMP` is set in which case
:cdata:`NPY_ALLOW_THREADS` is defined to be 0.
Group 1
"""""""
This group is used to call code that may take some time but does not
use any Python C-API calls. Thus, the GIL should be released during
its calculation.
.. cmacro:: NPY_BEGIN_ALLOW_THREADS
Equivalent to :cmacro:`Py_BEGIN_ALLOW_THREADS` except it uses
:cdata:`NPY_ALLOW_THREADS` to determine if the macro if
replaced with white-space or not.
.. cmacro:: NPY_END_ALLOW_THREADS
Equivalent to :cmacro:`Py_END_ALLOW_THREADS` except it uses
:cdata:`NPY_ALLOW_THREADS` to determine if the macro if
replaced with white-space or not.
.. cmacro:: NPY_BEGIN_THREADS_DEF
Place in the variable declaration area. This macro sets up the
variable needed for storing the Python state.
.. cmacro:: NPY_BEGIN_THREADS
Place right before code that does not need the Python
interpreter (no Python C-API calls). This macro saves the
Python state and releases the GIL.
.. cmacro:: NPY_END_THREADS
Place right after code that does not need the Python
interpreter. This macro acquires the GIL and restores the
Python state from the saved variable.
.. cfunction:: NPY_BEGIN_THREADS_DESCR(PyArray_Descr *dtype)
Useful to release the GIL only if *dtype* does not contain
arbitrary Python objects which may need the Python interpreter
during execution of the loop. Equivalent to
.. cfunction:: NPY_END_THREADS_DESCR(PyArray_Descr *dtype)
Useful to regain the GIL in situations where it was released
using the BEGIN form of this macro.
Group 2
"""""""
This group is used to re-acquire the Python GIL after it has been
released. For example, suppose the GIL has been released (using the
previous calls), and then some path in the code (perhaps in a
different subroutine) requires use of the Python C-API, then these
macros are useful to acquire the GIL. These macros accomplish
essentially a reverse of the previous three (acquire the LOCK saving
what state it had) and then re-release it with the saved state.
.. cmacro:: NPY_ALLOW_C_API_DEF
Place in the variable declaration area to set up the necessary
variable.
.. cmacro:: NPY_ALLOW_C_API
Place before code that needs to call the Python C-API (when it is
known that the GIL has already been released).
.. cmacro:: NPY_DISABLE_C_API
Place after code that needs to call the Python C-API (to re-release
the GIL).
.. tip::
Never use semicolons after the threading support macros.
Priority
^^^^^^^^
.. cvar:: NPY_PRIOIRTY
Default priority for arrays.
.. cvar:: NPY_SUBTYPE_PRIORITY
Default subtype priority.
.. cvar:: NPY_SCALAR_PRIORITY
Default scalar priority (very small)
.. cfunction:: double PyArray_GetPriority(PyObject* obj, double def)
Return the :obj:`__array_priority__` attribute (converted to a
double) of *obj* or *def* if no attribute of that name
exists. Fast returns that avoid the attribute lookup are provided
for objects of type :cdata:`PyArray_Type`.
Default buffers
^^^^^^^^^^^^^^^
.. cvar:: NPY_BUFSIZE
Default size of the user-settable internal buffers.
.. cvar:: NPY_MIN_BUFSIZE
Smallest size of user-settable internal buffers.
.. cvar:: NPY_MAX_BUFSIZE
Largest size allowed for the user-settable buffers.
Other constants
^^^^^^^^^^^^^^^
.. cvar:: NPY_NUM_FLOATTYPE
The number of floating-point types
.. cvar:: NPY_MAXDIMS
The maximum number of dimensions allowed in arrays.
.. cvar:: NPY_VERSION
The current version of the ndarray object (check to see if this
variable is defined to guarantee the numpy/arrayobject.h header is
being used).
.. cvar:: NPY_FALSE
Defined as 0 for use with Bool.
.. cvar:: NPY_TRUE
Defined as 1 for use with Bool.
.. cvar:: NPY_FAIL
The return value of failed converter functions which are called using
the "O&" syntax in :cfunc:`PyArg_ParseTuple`-like functions.
.. cvar:: NPY_SUCCEED
The return value of successful converter functions which are called
using the "O&" syntax in :cfunc:`PyArg_ParseTuple`-like functions.
Miscellaneous Macros
^^^^^^^^^^^^^^^^^^^^
.. cfunction:: PyArray_SAMESHAPE(a1, a2)
Evaluates as True if arrays *a1* and *a2* have the same shape.
.. cfunction:: PyArray_MAX(a,b)
Returns the maximum of *a* and *b*. If (*a*) or (*b*) are
expressions they are evaluated twice.
.. cfunction:: PyArray_MIN(a,b)
Returns the minimum of *a* and *b*. If (*a*) or (*b*) are
expressions they are evaluated twice.
.. cfunction:: PyArray_CLT(a,b)
.. cfunction:: PyArray_CGT(a,b)
.. cfunction:: PyArray_CLE(a,b)
.. cfunction:: PyArray_CGE(a,b)
.. cfunction:: PyArray_CEQ(a,b)
.. cfunction:: PyArray_CNE(a,b)
Implements the complex comparisons between two complex numbers
(structures with a real and imag member) using NumPy's definition
of the ordering which is lexicographic: comparing the real parts
first and then the complex parts if the real parts are equal.
.. cfunction:: PyArray_REFCOUNT(PyObject* op)
Returns the reference count of any Python object.
.. cfunction:: PyArray_XDECREF_ERR(PyObject \*obj)
DECREF's an array object which may have the :cdata:`NPY_UPDATEIFCOPY`
flag set without causing the contents to be copied back into the
original array. Resets the :cdata:`NPY_WRITEABLE` flag on the base
object. This is useful for recovering from an error condition when
:cdata:`NPY_UPDATEIFCOPY` is used.
Enumerated Types
^^^^^^^^^^^^^^^^
.. ctype:: NPY_SORTKIND
A special variable-type which can take on the values :cdata:`NPY_{KIND}`
where ``{KIND}`` is
**QUICKSORT**, **HEAPSORT**, **MERGESORT**
.. cvar:: NPY_NSORTS
Defined to be the number of sorts.
.. ctype:: NPY_SCALARKIND
A special variable type indicating the number of "kinds" of
scalars distinguished in determining scalar-coercion rules. This
variable can take on the values :cdata:`NPY_{KIND}` where ``{KIND}`` can be
**NOSCALAR**, **BOOL_SCALAR**, **INTPOS_SCALAR**,
**INTNEG_SCALAR**, **FLOAT_SCALAR**, **COMPLEX_SCALAR**,
**OBJECT_SCALAR**
.. cvar:: NPY_NSCALARKINDS
Defined to be the number of scalar kinds
(not including :cdata:`NPY_NOSCALAR`).
.. ctype:: NPY_ORDER
A variable type indicating the order that an array should be
interpreted in. The value of a variable of this type can be
:cdata:`NPY_{ORDER}` where ``{ORDER}`` is
**ANYORDER**, **CORDER**, **FORTRANORDER**
.. ctype:: NPY_CLIPMODE
A variable type indicating the kind of clipping that should be
applied in certain functions. The value of a variable of this type
can be :cdata:`NPY_{MODE}` where ``{MODE}`` is
**CLIP**, **WRAP**, **RAISE**
.. index::
pair: ndarray; C-API