Adam DePrince <[EMAIL PROTECTED]> wrote:
> Each iteration of os.walk returns three parameters; one of those, dirs,
> is a list of directories within the current directory pointed at by
> root.
Yes, it does.
> Am I correct to assume that you beleve that by changing the contents of
> dir you will affect how os.walk traverses the directories. If so, that
> is your problem.
It's not a problem: it's a correct description of os.walk behavior.
> When looping in a for loop, it is generally good programming practice to
> assume that nothing you do within your loop will affect which
> root,dir,files tuples have been set aside to loop over. It is likely
> that once os.walk was called, the items to be iterated over are
> predestined (i.e. assume you are iterating over a tuple.)
"Likely"? I think it's generally good programming practice to read the
docs. help(os.walk) says:
When topdown is true, the caller can modify the dirnames list in-place
(e.g., via del or slice assignment), and walk will only recurse into the
subdirectories whose names remain in dirnames; this can be used to prune
the search, or to impose a specific order of visiting. Modifying
and topdown is true by default. The problem was just that the poster
was not using the right way to "modify the dirnames list in-place", as
he was looping on said list rather than a copy and yet modifying what he
was looping on (two suggestions i saw were "loop on a copy", once
obtained with the odd but popular Python idiom somelist[:], once with
the much more readable approach list(somelist)...). The best
alternative is often to use a list comprehension, with somelist[:] on
the left of the assignment since you do need to modify in-place. I.e.,
say that, generically speaking, you're trying (and failing) to do:
for item in alist:
if isnasty(item):
alist.remove(item)
changing the header to ``in alist[:]:'' or ``in list(alist):'' probably
makes this code work, but it still can't make it GOOD... good would be:
alist[:] = [item for item in alist if not isnasty(item)]
Alex
--
http://mail.python.org/mailman/listinfo/python-list
