Redundant use of generators? (Python)

Question

say we did the following: (ignore if this is silly or if there is a better way, it's a simplified example)

from itertools import izip

def check(someList):
    for item in someList:
        yield item[0]

for items in izip(check(someHugeList1), check(someHugeList2)):
    //some logic

since check is a generator, is it redundant to use izip? Would using regular zip be just as good?

Answer 1

Regular zip() would expand the whole generator first. You wouldn't want to do that with a huge or endless generator.

Demo:

>>> def gen():
...     print 'generating'
...     yield 'a'
... 
>>> gen()
<generator object gen at 0x10747f320>
>>> zip(gen(), gen())
generating
generating
[('a', 'a')]

Note that directly creating the generator doesn't print anything; the generator is still in the paused state. But passing the generator to zip() immediately produces output, which can only be produced by iterating over the generators in full.