On 4/25/2014 2:04 PM, Matthew Barnett wrote:
On 2014-04-25 18:53, Charles Hixson 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?
The other way is to build a new dictionary.
If you expect to delete more than half the keys *and* if there are no
other references to the dict, such that you need the particular object
mutated, this might be better.
Actually, there's a third way. Iterate over a snapshot:
for (k, v) in list(m.items()):
if f(k):
# do some processing of v and save result elsewhere
del m[k]
Since a pre-snapshot of items or even just keys will be longer than a
list of keys to be deleted, I would stick with the latter.
--
Terry Jan Reedy
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