2.3 list reverse() bug?

[Alex Martelli]

Bjorn Pettersen wrote:
   ...
> There are of course times where a copy is needed (e.g. multi-version
> scenarios) but most programmers don't bump into these very frequently...

Here's my candidate for "most frequent scenario where copies are needed":

for item in somelist:
    if froobable(item):
        somelist.append(frooble(item))
    elif uncadable(item):
        somelist.remove(item)

i.e.: you want to modify the very list you're looping on.  This is one
of Python's few but important "traps and pitfalls".  The simplest fix:

for item in list(somelist):
    ...same as above...

list(x) is my favourite way to make a shallow copy of list x, but x[:]
and copy.copy(x) are essentially equivalent.


Alex