Different ways of clearing lists

Become part of the top 3% of the developers by applying to Toptal https://topt.al/25cXVn

--

Track title: CC H Dvoks String Quartet No 12 Ame

--

Chapters
00:00 Question
00:27 Accepted answer (Score 384)
01:01 Answer 2 (Score 73)
01:44 Answer 3 (Score 38)
02:03 Answer 4 (Score 13)
02:26 Thank you

--

Full question
https://stackoverflow.com/questions/8507...

Answer 1 links:
[Mutable Sequence Types]: https://docs.python.org/dev/library/stdt...

--

Content licensed under CC BY-SA
https://meta.stackexchange.com/help/lice...

--

Tags
#python #list

#avk47

ACCEPTED ANSWER

Score 386

Clearing a list in place will affect all other references of the same list.

For example, this method doesn't affect other references:

>>> a = [1, 2, 3]
>>> b = a
>>> a = []
>>> print(a)
[]
>>> print(b)
[1, 2, 3]

But this one does:

>>> a = [1, 2, 3]
>>> b = a
>>> del a[:]      # equivalent to   del a[0:len(a)]
>>> print(a)
[]
>>> print(b)
[]
>>> a is b
True

You could also do:

>>> a[:] = []

ANSWER 2

Score 38

There is a very simple way to clear a python list. Use del list_name[:].

For example:

>>> a = [1, 2, 3]
>>> b = a
>>> del a[:]
>>> print a, b
[] []

ANSWER 3

Score 13

~~It appears to me that del will give you the memory back, while assigning a new list will make the old one be deleted only when the gc runs.matter.~~

This may be useful for large lists, but for small list it should be negligible.

Edit: As Algorias, it doesn't matter.

Note that

del old_list[ 0:len(old_list) ]

is equivalent to

del old_list[:]

ANSWER 4

Score 10

del list[:]

Will delete the values of that list variable

del list

Will delete the variable itself from memory