ValueError: cannot reshape array of size X into shape Y

ValueError: cannot reshape array

$ python -c "import numpy as np; a=np.arange(10); a.reshape((3,4))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: cannot reshape array of size 10 into shape (3,4)

Why this happens

Reshape requires the total number of elements to remain unchanged. 10 cannot be reshaped into 3*4=12 elements.

Fix

Choose a target shape whose product equals the number of elements, or use -1 to infer one dimension when possible.

Wrong code

import numpy as np
a = np.arange(10)
print(a.reshape((3,4)))

Fixed code

import numpy as np
a = np.arange(12)
print(a.reshape((3,4)))

# or infer
a = np.arange(10)
print(a.reshape((2, -1)))  # -> (2,5)