numpy.sum(a, axis=None, dtype=None, out=None)

Sum of array elements over a given axis.

Parameters :

a : array_like

Elements to sum.

axis : integer, optional

Axis over which the sum is taken. By default axis is None, and all elements are summed.

dtype : dtype, optional

The type of the returned array and of the accumulator in which the elements are summed. By default, the dtype of a is used. An exception is when a has an integer type with less precision than the default platform integer. In that case, the default platform integer is used instead.

out : ndarray, optional

Array into which the output is placed. By default, a new array is created. If out is given, it must be of the appropriate shape (the shape of a with axis removed, i.e., numpy.delete(a.shape, axis)). Its type is preserved. See doc.ufuncs (Section “Output arguments”) for more details.

Returns :

sum_along_axis : ndarray

An array with the same shape as a, with the specified axis removed. If a is a 0-d array, or if axis is None, a scalar is returned. If an output array is specified, a reference to out is returned.

See also

Equivalent method.
Cumulative sum of array elements.
Integration of array values using the composite trapezoidal rule.

mean, average


Arithmetic is modular when using integer types, and no error is raised on overflow.


>>> np.sum([0.5, 1.5])
>>> np.sum([0.5, 0.7, 0.2, 1.5], dtype=np.int32)
>>> np.sum([[0, 1], [0, 5]])
>>> np.sum([[0, 1], [0, 5]], axis=0)
array([0, 6])
>>> np.sum([[0, 1], [0, 5]], axis=1)
array([1, 5])

If the accumulator is too small, overflow occurs:

>>> np.ones(128, dtype=np.int8).sum(dtype=np.int8)

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