Data Type API
=============
.. sectionauthor:: Travis E. Oliphant
The standard array can have 24 different data types (and has some
support for adding your own types). These data types all have an
enumerated type, an enumerated type-character, and a corresponding
array scalar Python type object (placed in a hierarchy). There are
also standard C typedefs to make it easier to manipulate elements of
the given data type. For the numeric types, there are also bit-width
equivalent C typedefs and named typenumbers that make it easier to
select the precision desired.
.. warning::
The names for the types in c code follows c naming conventions
more closely. The Python names for these types follow Python
conventions. Thus, :cdata:`NPY_FLOAT` picks up a 32-bit float in
C, but :class:`numpy.float_` in Python corresponds to a 64-bit
double. The bit-width names can be used in both Python and C for
clarity.
Enumerated Types
----------------
There is a list of enumerated types defined providing the basic 24
data types plus some useful generic names. Whenever the code requires
a type number, one of these enumerated types is requested. The types
are all called :cdata:`NPY_{NAME}`:
.. cvar:: NPY_BOOL
The enumeration value for the boolean type, stored as one byte.
It may only be set to the values 0 and 1.
.. cvar:: NPY_BYTE
.. cvar:: NPY_INT8
The enumeration value for an 8-bit/1-byte signed integer.
.. cvar:: NPY_SHORT
.. cvar:: NPY_INT16
The enumeration value for a 16-bit/2-byte signed integer.
.. cvar:: NPY_INT
.. cvar:: NPY_INT32
The enumeration value for a 32-bit/4-byte signed integer.
.. cvar:: NPY_LONG
Equivalent to either NPY_INT or NPY_LONGLONG, depending on the
platform.
.. cvar:: NPY_LONGLONG
.. cvar:: NPY_INT64
The enumeration value for a 64-bit/8-byte signed integer.
.. cvar:: NPY_UBYTE
.. cvar:: NPY_UINT8
The enumeration value for an 8-bit/1-byte unsigned integer.
.. cvar:: NPY_USHORT
.. cvar:: NPY_UINT16
The enumeration value for a 16-bit/2-byte unsigned integer.
.. cvar:: NPY_UINT
.. cvar:: NPY_UINT32
The enumeration value for a 32-bit/4-byte unsigned integer.
.. cvar:: NPY_ULONG
Equivalent to either NPY_UINT or NPY_ULONGLONG, depending on the
platform.
.. cvar:: NPY_ULONGLONG
.. cvar:: NPY_UINT64
The enumeration value for a 64-bit/8-byte unsigned integer.
.. cvar:: NPY_HALF
.. cvar:: NPY_FLOAT16
The enumeration value for a 16-bit/2-byte IEEE 754-2008 compatible floating
point type.
.. cvar:: NPY_FLOAT
.. cvar:: NPY_FLOAT32
The enumeration value for a 32-bit/4-byte IEEE 754 compatible floating
point type.
.. cvar:: NPY_DOUBLE
.. cvar:: NPY_FLOAT64
The enumeration value for a 64-bit/8-byte IEEE 754 compatible floating
point type.
.. cvar:: NPY_LONGDOUBLE
The enumeration value for a platform-specific floating point type which is
at least as large as NPY_DOUBLE, but larger on many platforms.
.. cvar:: NPY_CFLOAT
.. cvar:: NPY_COMPLEX64
The enumeration value for a 64-bit/8-byte complex type made up of
two NPY_FLOAT values.
.. cvar:: NPY_CDOUBLE
.. cvar:: NPY_COMPLEX128
The enumeration value for a 128-bit/16-byte complex type made up of
two NPY_DOUBLE values.
.. cvar:: NPY_CLONGDOUBLE
The enumeration value for a platform-specific complex floating point
type which is made up of two NPY_LONGDOUBLE values.
.. cvar:: NPY_DATETIME
The enumeration value for a data type which holds dates or datetimes with
a precision based on selectable date or time units.
.. cvar:: NPY_TIMEDELTA
The enumeration value for a data type which holds lengths of times in
integers of selectable date or time units.
.. cvar:: NPY_STRING
The enumeration value for ASCII strings of a selectable size. The
strings have a fixed maximum size within a given array.
.. cvar:: NPY_UNICODE
The enumeration value for UCS4 strings of a selectable size. The
strings have a fixed maximum size within a given array.
.. cvar:: NPY_OBJECT
The enumeration value for references to arbitrary Python objects.
.. cvar:: NPY_VOID
Primarily used to hold struct dtypes, but can contain arbitrary
binary data.
Some useful aliases of the above types are
.. cvar:: NPY_INTP
The enumeration value for a signed integer type which is the same
size as a (void \*) pointer. This is the type used by all
arrays of indices.
.. cvar:: NPY_UINTP
The enumeration value for an unsigned integer type which is the
same size as a (void \*) pointer.
.. cvar:: NPY_MASK
The enumeration value of the type used for masks, such as with
the :cdata:`NPY_ITER_ARRAYMASK` iterator flag. This is equivalent
to :cdata:`NPY_UINT8`.
.. cvar:: NPY_DEFAULT_TYPE
The default type to use when no dtype is explicitly specified, for
example when calling np.zero(shape). This is equivalent to
:cdata:`NPY_DOUBLE`.
Other useful related constants are
.. cvar:: NPY_NTYPES
The total number of built-in NumPy types. The enumeration covers
the range from 0 to NPY_NTYPES-1.
.. cvar:: NPY_NOTYPE
A signal value guaranteed not to be a valid type enumeration number.
.. cvar:: NPY_USERDEF
The start of type numbers used for Custom Data types.
The various character codes indicating certain types are also part of
an enumerated list. References to type characters (should they be
needed at all) should always use these enumerations. The form of them
is :cdata:`NPY_{NAME}LTR` where ``{NAME}`` can be
**BOOL**, **BYTE**, **UBYTE**, **SHORT**, **USHORT**, **INT**,
**UINT**, **LONG**, **ULONG**, **LONGLONG**, **ULONGLONG**,
**HALF**, **FLOAT**, **DOUBLE**, **LONGDOUBLE**, **CFLOAT**,
**CDOUBLE**, **CLONGDOUBLE**, **DATETIME**, **TIMEDELTA**,
**OBJECT**, **STRING**, **VOID**
**INTP**, **UINTP**
**GENBOOL**, **SIGNED**, **UNSIGNED**, **FLOATING**, **COMPLEX**
The latter group of ``{NAME}s`` corresponds to letters used in the array
interface typestring specification.
Defines
-------
Max and min values for integers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. cvar:: NPY_MAX_INT{bits}
.. cvar:: NPY_MAX_UINT{bits}
.. cvar:: NPY_MIN_INT{bits}
These are defined for ``{bits}`` = 8, 16, 32, 64, 128, and 256 and provide
the maximum (minimum) value of the corresponding (unsigned) integer
type. Note: the actual integer type may not be available on all
platforms (i.e. 128-bit and 256-bit integers are rare).
.. cvar:: NPY_MIN_{type}
This is defined for ``{type}`` = **BYTE**, **SHORT**, **INT**,
**LONG**, **LONGLONG**, **INTP**
.. cvar:: NPY_MAX_{type}
This is defined for all defined for ``{type}`` = **BYTE**, **UBYTE**,
**SHORT**, **USHORT**, **INT**, **UINT**, **LONG**, **ULONG**,
**LONGLONG**, **ULONGLONG**, **INTP**, **UINTP**
Number of bits in data types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All :cdata:`NPY_SIZEOF_{CTYPE}` constants have corresponding
:cdata:`NPY_BITSOF_{CTYPE}` constants defined. The :cdata:`NPY_BITSOF_{CTYPE}`
constants provide the number of bits in the data type. Specifically,
the available ``{CTYPE}s`` are
**BOOL**, **CHAR**, **SHORT**, **INT**, **LONG**,
**LONGLONG**, **FLOAT**, **DOUBLE**, **LONGDOUBLE**
Bit-width references to enumerated typenums
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All of the numeric data types (integer, floating point, and complex)
have constants that are defined to be a specific enumerated type
number. Exactly which enumerated type a bit-width type refers to is
platform dependent. In particular, the constants available are
:cdata:`PyArray_{NAME}{BITS}` where ``{NAME}`` is **INT**, **UINT**,
**FLOAT**, **COMPLEX** and ``{BITS}`` can be 8, 16, 32, 64, 80, 96, 128,
160, 192, 256, and 512. Obviously not all bit-widths are available on
all platforms for all the kinds of numeric types. Commonly 8-, 16-,
32-, 64-bit integers; 32-, 64-bit floats; and 64-, 128-bit complex
types are available.
Integer that can hold a pointer
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The constants **NPY_INTP** and **NPY_UINTP** refer to an
enumerated integer type that is large enough to hold a pointer on the
platform. Index arrays should always be converted to **NPY_INTP**
, because the dimension of the array is of type npy_intp.
C-type names
------------
There are standard variable types for each of the numeric data types
and the bool data type. Some of these are already available in the
C-specification. You can create variables in extension code with these
types.
Boolean
^^^^^^^
.. ctype:: npy_bool
unsigned char; The constants :cdata:`NPY_FALSE` and
:cdata:`NPY_TRUE` are also defined.
(Un)Signed Integer
^^^^^^^^^^^^^^^^^^
Unsigned versions of the integers can be defined by pre-pending a 'u'
to the front of the integer name.
.. ctype:: npy_(u)byte
(unsigned) char
.. ctype:: npy_(u)short
(unsigned) short
.. ctype:: npy_(u)int
(unsigned) int
.. ctype:: npy_(u)long
(unsigned) long int
.. ctype:: npy_(u)longlong
(unsigned long long int)
.. ctype:: npy_(u)intp
(unsigned) Py_intptr_t (an integer that is the size of a pointer on
the platform).
(Complex) Floating point
^^^^^^^^^^^^^^^^^^^^^^^^
.. ctype:: npy_(c)float
float
.. ctype:: npy_(c)double
double
.. ctype:: npy_(c)longdouble
long double
complex types are structures with **.real** and **.imag** members (in
that order).
Bit-width names
^^^^^^^^^^^^^^^
There are also typedefs for signed integers, unsigned integers,
floating point, and complex floating point types of specific bit-
widths. The available type names are
:ctype:`npy_int{bits}`, :ctype:`npy_uint{bits}`, :ctype:`npy_float{bits}`,
and :ctype:`npy_complex{bits}`
where ``{bits}`` is the number of bits in the type and can be **8**,
**16**, **32**, **64**, 128, and 256 for integer types; 16, **32**
, **64**, 80, 96, 128, and 256 for floating-point types; and 32,
**64**, **128**, 160, 192, and 512 for complex-valued types. Which
bit-widths are available is platform dependent. The bolded bit-widths
are usually available on all platforms.
Printf Formatting
-----------------
For help in printing, the following strings are defined as the correct
format specifier in printf and related commands.
:cdata:`NPY_LONGLONG_FMT`, :cdata:`NPY_ULONGLONG_FMT`,
:cdata:`NPY_INTP_FMT`, :cdata:`NPY_UINTP_FMT`,
:cdata:`NPY_LONGDOUBLE_FMT`