Why python returns None for variable that assign for itself?

Question

I'm studying python, and it comes to me:

>>> a[0] = [1].append("test")
>>> a
[None, 2, 3, 4]

Expanding...

>>> a = [1,2,3,4]
>>> a[0]
1
>>> a[0] = [a[0]]
>>> a
[[1], 2, 3, 4]
>>> a[0].append(2)
>>> a
[[1, 2], 2, 3, 4]
>>> a[0].append("Batata")
>>> a
[[1, 2, 'Batata'], 2, 3, 4]

Why the short sentence [1].append("test") does not work?

`list.append()` returns `None`, that's why. – bereal Feb 11 '21 at 15:16 — bereal, Feb 11 '21 at 15:16
Try `+=` instead of `append`: `a[0] += ['whatever']`. – anatolyg Feb 11 '21 at 15:20 — anatolyg, Feb 11 '21 at 15:20

score 1 · Accepted Answer · answered Feb 11 '21 at 15:16

1

append() method works in-place and returns None.

So, if you do the following, b will have the value None:

a = []
b = a.append("test")
print(b)

answered Feb 11 '21 at 15:16

Krishna Chaurasia

8,924
6
22
35

1

Duplicates should be closed, not answered. See the Answer Well-Asked Questions section of How to Answer. – Charles Duffy Feb 11 '21 at 15:18

Why python returns None for variable that assign for itself?

1 Answers1