TypeError / ValueError: invalid broadcast assignment

TypeError/ValueError: invalid broadcast assignment

$ python -c "import numpy as np; a=np.zeros((2,3)); a[:,0]=np.array([1,2,3])"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: could not broadcast input array from shape (3,) into shape (2,)

Why this happens

You attempted to assign an array whose shape can’t be broadcast to the target slice/array shape. Broadcasting requires compatible trailing dimensions or singleton dimensions.

Fix

Reshape or expand dimensions to match, or ensure you assign an array with the correct shape.

Wrong code

import numpy as np
a = np.zeros((2,3))
a[:,0] = np.array([1,2,3])

Fixed code

import numpy as np
a = np.zeros((2,3))
a[:,0] = np.array([1,2])  # length 2 matches

# or reshape
vals = np.array([1,2,3]).reshape(3,1)
# assign to a compatible target
b = np.zeros((3,1))
b[:] = vals