`numpy:append`

source: /dev/numpy/build-install/usr/lib/python3.14/site-packages/numpy/lib/_function_base_impl.py:5567

Signature

def append(arr, values, axis = None)

Summary

Append values to the end of an array.

Parameters

arr : array_like: Values are appended to a copy of this array.
values : array_like: These values are appended to a copy of arr. It must be of the correct shape (the same shape as arr, excluding axis). If axis is not specified, values can be any shape and will be flattened before use.
axis : int, optional: The axis along which values are appended. If axis is not given, both arr and values are flattened before use.

Returns

append : ndarray: A copy of arr with values appended to axis. Note that append does not occur in-place: a new array is allocated and filled. If axis is None, out is a flattened array.

Examples

import numpy as np
np.append([1, 2, 3], [[4, 5, 6], [7, 8, 9]])

✓

array([1, 2, 3, 4, 5, 6, 7, 8, 9])

When `axis` is specified, `values` must have the correct shape.

np.append([[1, 2, 3], [4, 5, 6]], [[7, 8, 9]], axis=0)

✓

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])

np.append([[1, 2, 3], [4, 5, 6]], [7, 8, 9], axis=0)

✗

Traceback (most recent call last):
  File "<doctest numpy:append[0]>", line 1, in <module>
    np.append([[1, 2, 3], [4, 5, 6]], [7, 8, 9], axis=0)
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/dev/numpy/build-install/usr/lib/python3.14/site-packages/numpy/lib/_function_base_impl.py", line 5634, in append
    return concatenate((arr, values), axis=axis)
ValueError: all the input arrays must have same number of dimensions, but the array at index 0 has 2 dimension(s) and the array at index 1 has 1 dimension(s)

a = np.array([1, 2], dtype=int)
c = np.append(a, [])
c

✓

array([1., 2.])

c.dtype

✗

dtype('float64')

Default dtype for empty ndarrays is `float64` thus making the output of dtype `float64` when appended with dtype `int64`

Aliases