why doesnt numpy create an array when executing a list method-CodePudding

playing around with numpy:

import numpy as np
l = [39, 54, 72, 46, 89, 53, 96, 64, 2, 75]
nl = np.array(l.append(3))


>> array(None, dtype=object)

now, if i call on l, i'll get the new list: [39, 54, 72, 46, 89, 53, 96, 64, 2, 75, 3]

my question is, why doesn't numpy create that list as an array?

if i do something like this:

nl = np.array(l.extend([45])) i get the same thing.

but if try to concatenate without a method: nl = np.array(l [45]) it works.

so, is it because numpy is trying to create the array before the method is called? or what?

CodePudding user response：

The append function will always return None. You must do this in two different lines of code:

import numpy as np
l = [39, 54, 72, 46, 89, 53, 96, 64, 2, 75]
l.append(3)
nl = np.array(l)

CodePudding user response：

append and extend are in-place methods and return None.

print(l.append(3)) # None
print(l.extend([3])) # None