Most elegant way to branch if a generator is empty in Python

Question

I have a generator in Python, and I want to loop over it if it has items, and perform a different action if it is empty. Something like

if generator is empty:
    perform some action
else:
    for item in generator:
        perform some actions

I know there is no way to tell if a generator is empty without iterating through it, but it seems that there should still be some nice elegant way to perform this logic. The best I can think of is something along the lines of https://stackoverflow.com/a/664239/161801, which seems very inelegant, I guess because it has to treat the first element of the generator separately from the rest.

You could iterate over all the items and set a flag ("there was an item") inside the loop and do the alternate action if the flag was not set — hlt, Aug 15 '14 at 19:40
@njzk2 I obviously know about that question (I linked to it), but I think it is different. That question is asking if it is possible to know if a generator is empty without iterating through it. I already know that this is not possible due to the way that generators work. I am asking for a clean way to work with this limitation. — asmeurer, Aug 15 '14 at 19:41
@asmeurer there are several different answers and approaches in the linked question - what are your problems with them? This doesn't really seem like a separate question. — jonrsharpe, Aug 15 '14 at 19:43
@asmeurer the answer you linked to is as good as it gets I'm afraid — Jon Clements, Aug 15 '14 at 19:45
This is what I initially thought (and sometimes wish) that `for else` meant in Python. Unfortunately it means something a little different. — asmeurer, Aug 15 '14 at 19:46
@asmeurer all the options are in the duplicate - Python hasn't evolved a new way of doing what you want since that was answered... — Jon Clements, Aug 15 '14 at 19:50

score 4 · Answer 1 · answered Aug 15 '14 at 19:42

4

Just set a flag if the generator is not empty:

isGeneratorEmpty = True
for item in generator:
    isGeneratorEmpty = False
    perform some actions

if isGeneratorEmpty:
    perform some actions

answered Aug 15 '14 at 19:42

jh314

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[Source?](http://stackoverflow.com/a/7971996/1454048) – admdrew Aug 15 '14 at 19:43
3

@admdrew The logic is pretty straightforward (someone suggested the same thing in the comments), jh314 probably came up with it independently. – dano Aug 15 '14 at 19:45

Most elegant way to branch if a generator is empty in Python

1 Answers1