Python Forum

the documentation for the .pop() method for mutable sequences says that the argument to be passed to it is a number in a list.  why is that?

That "list" notation is common for indicating that it's optional. So you provide either a number, or nothing.

Other readers can see https://docs.python.org/3.7/tutorial/dat...tures.html for an example.

so [[]] can mean an optional empty list. or for more fun [[n]] can mean an optional list with n as its only member or a list that can optionally have a member n or be empty.

I'd have to see a real example.

(May-18-2017, 03:48 AM)micseydel Wrote: [ -> ]I'd have to see a real example.

how would i do that?  i'm just making mixed interpretation of [] ehen there are two of them, one interpreted as a list spec and the other meaning optional.

You pop(index) out of the sequence

>>> l = list(range(1, 21))

>>> l
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

>>> for index, _ in enumerate(l):
...     print(l.pop(index+1))
2
4
6
8
10
12
14
16
18
20

>>> l
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]