AttributeError: 'numpy.ndarray' object has no attribute 'append'

AttributeError: ‘numpy.ndarray’ object has no attribute ‘append’

$ python -c "import numpy as np; a = np.array([1,2,3]); a.append(4)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'append'

Why this happens

NumPy arrays are fixed-size blocks of memory and don’t support list methods like append. Users often confuse list API with ndarray.

Fix

Use np.append, np.concatenate, or build a Python list and convert to an array when dynamically growing data.

Wrong code

import numpy as np
a = np.array([1,2,3])
a.append(4)

Fixed code

import numpy as np
a = np.array([1,2,3])
 a2 = np.append(a, 4)
print(a2)

# or use concatenate
 a3 = np.concatenate([a, np.array([4])])
print(a3)

# or collect in list then convert
lst = [1,2,3]
lst.append(4)
arr = np.array(lst)