Two simultaneous generator functions, Python

Question

I have two functions:

def a():
    while True:
        yield stuff

def b():
    while True:
        yield otherstuff

and I want to have a loop which collects one yield from each function stored in a for a() and b for b() ; for example. If I nest the for loops which call them, it restarts the 2nd generator every-time the first loop loops. Can I have any help with this?

Thanks!

Sukrit Kalra · Accepted Answer · 2013-08-31 19:31:31Z

6

You could use itertools.izip(...) to zip the values together.

>>> def a():
        for i in xrange(10):
            yield i


>>> def b():
        for i in xrange(10, 20):
            yield i


>>> from itertools import izip
>>> for i, j in izip(a(), b()):
        print i, j


0 10
1 11
2 12
3 13
4 14
5 15
6 16
7 17
8 18
9 19

edited Aug 31, 2013 at 19:31

answered Aug 31, 2013 at 19:26

Sukrit Kalra

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user2357112 · Accepted Answer · 2013-08-31 19:26:22Z

3

for x, y in zip(a(), b()):

It's just like simultaneously looping over any two sequences. (You may want to use itertools.izip or from future_builtins import zip to avoid gathering all the items into a big list before iterating.)

answered Aug 31, 2013 at 19:26

user2357112

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2 Comments

Sukrit Kalra Over a year ago

I don't think zip(...) would work with an infinite generator which seems to be OP's intent. Correct me if I am wrong. :)

user2357112 Over a year ago

@SukritKalra: Huh. I didn't actually read the given generators; I probably should have. They are indeed infinite, so izip or future-zip would probably be appropriate.

roman · Accepted Answer · 2013-08-31 19:26:34Z

1

You can use izip from itertools

from itertools import izip
z = izip(a(),b())

now you have generator of tuples, first item from a() and second from b()

answered Aug 31, 2013 at 19:26

roman

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