list.reverse()

[John Hunter]

>>>>> "Mike" == Mike Dean <klaatu at evertek.net> writes:

    Mike> I think I recall seeing a reasonable explanation for this
    Mike> earlier (probably referring actually to list.sort()), but
    Mike> I'm wondering - what was the rationale for making
    Mike> list.reverse() reverse a list in-place rather than return a
    Mike> new, reversed list?  I'm sure there's a good reason, but
    Mike> what might that be?

Efficiency.  You may not need a copy of both the list and the reversed
list. 

This gives you the choice of convenience (add your own copy semantics)
or efficiency.  If reverse always returned a copy, you'd be stuck with
convenience or writing your own in place reverse (which is harder than
writing your own copy)

class mylist(list):
    def reversecopy(self):
        new = self[:]
        new.reverse()
        return new

x = mylist([1,2,3,4])

y = x.reversecopy()
print x
print y


John Hunter