Fix Python – Different ways of clearing lists

Question

Asked By – johannix

Is there any reason to do anything more complicated than one of these two lines when you want to clear a list in Python?

old_list = []
old_list = list()

The reason I ask is that I just saw this in some running code:

del old_list[ 0:len(old_list) ]

Now we will see solution for issue: Different ways of clearing lists


Answer

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[:] = []

This question is answered By – Koba

This answer is collected from stackoverflow and reviewed by FixPython community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0