On Sat, Apr 26, 2014 at 3:53 AM, Charles Hixson
<charleshi...@earthlink.net> wrote:
> What is the proper way to delete selected items during iteration of a map?
> What I want to do is:
>
> for (k, v) in m.items():
> if f(k):
> # do some processing of v and save result elsewhere
> del m[k]
>
> But this gives (as should be expected):
> RuntimeError: dictionary changed size during iteration
> In the past I've accumulated the keys to be deleted in a separate list, but
> this time there are likely to be a large number of them, so is there some
> better way?
One easy way is to explicitly coalesce the items() view into a list:
for k, v in list(m.items()):
That would work, but you effectively duplicate your entire dictionary
into a list. More likely, you should simply snapshot the keys:
for k in list(m):
# Your example code isn't using v, but I
# assume the real code does
v = m[k]
if f(k):
# as above
del m[k]
This and your previous technique of accumulating a delete-me list
would be the two standard ways to filter a dictionary with a loop. (I
say "with a loop" because there's a third way to filter a dictionary,
and that's with a comprehension. But I don't know of a really clean
way to save v elsewhere for the cases where the dict isn't keeping
that key.)
ChrisA
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