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How do I merge two python iterators?

Asked 2008-10-28T16:07:12.883
31

I have two iterators, a list and an itertools.count object (i.e. an infinite value generator). I would like to merge these two into a resulting iterator that will alternate yield values between the two:

>>> import itertools
>>> c = itertools.count(1)
>>> items = ['foo', 'bar']
>>> merged = imerge(items, c)  # the mythical "imerge"
>>> merged.next()
'foo'
>>> merged.next()
1
>>> merged.next()
'bar'
>>> merged.next()
2
>>> merged.next()
Traceback (most recent call last):
    ...
StopIteration

What is the simplest, most concise way to do this?

python merge iterator
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3 Answers

46

A generator will solve your problem nicely.

def imerge(a, b):
    for i, j in itertools.izip(a,b):
        yield i
        yield j
answered 2008-10-28T16:14:02.387
11

You can use zip as well as itertools.chain. This will only work if the first list is finite:

merge=itertools.chain(*[iter(i) for i in zip(['foo', 'bar'], itertools.count(1))])
answered 2008-10-28T16:15:15.707
3

I'm not sure what your application is, but you might find the enumerate() function more useful.

>>> items = ['foo', 'bar', 'baz']
>>> for i, item in enumerate(items):
...  print item
...  print i
... 
foo
0
bar
1
baz
2
answered 2008-10-28T22:03:08.500

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