Iterate over all pairs of consecutive items in a list

python list iterator

flonk · Jan 23, 2014 · Viewed 40.4k times · Source

Given a list

l = [1, 7, 3, 5]

I want to iterate over all pairs of consecutive list items (1,7), (7,3), (3,5), i.e.

for i in xrange(len(l) - 1):
    x = l[i]
    y = l[i + 1]
    # do something

I would like to do this in a more compact way, like

for x, y in someiterator(l): ...

Is there a way to do do this using builtin Python iterators? I'm sure the itertools module should have a solution, but I just can't figure it out.

Answer

Just use zip

>>> l = [1, 7, 3, 5]
>>> for first, second in zip(l, l[1:]):
...     print first, second
...
1 7
7 3
3 5

As suggested you might consider using the izip function in itertools for very long lists where you don't want to create a new list.

import itertools

for first, second in itertools.izip(l, l[1:]):
    ...