How to fix “TypeError: len() of unsized object”

Use the arrays’ size attribute instead:

nv = v.size
nu = u.size

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You also probably want to use numpy.fromstring to take and convert the input string into an array:

>>> v = np.fromstring(input('enter the elements of the vector separated by comma: '), dtype=int, sep=',')
enter the elements of the vector separated by comma: 1, 2, 3
>>> v
array([1, 2, 3])
>>> len(v)
3
>>> v.size
3