Steven Watanabe wrote:
> I know that the standard idioms for clearing a list are:
>
> (1) mylist[:] = []
> (2) del mylist[:]
>
> I guess I'm not in the "slicing frame of mind", as someone put it, but
> can someone explain what the difference is between these and:
>
> (3) mylist = []
>
> Why are (1) and (2) preferred? I think the first two are changing the
> list in-place, but why is that better? Isn't the end result the same?
No. Consider this simple example:
class Foo(object):
def __init__(self, all_my_thingies):
self.all_my_thingies = all_my_thingies
things = [1,2,3,4,5]
f = Foo(things)
things = [] # I've been robbed
print f.all_my_thingies # or not?
The reason is that l = [] just rebinds a new object (a list, but it could be
anything) to a name, while l[:] = [] will alter the object _referred_ to by
l. That is a HUGE difference!
Diez
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