How to iterate through 2 lists at once?

Question

with open('myfile.txt') as f:
    for line in f: 
        doSomething(line)

Is there a way to iterate through two files at once? Here's some pseudo code to help you understand..

with open('myfile.txt') as f: and with open ('myfile2.txt') as d:
    for line in f and for line2 in d:
        doSomething(line, line2)

why don't you use zip()? – Sharif Mamun May 05 '14 at 19:49 — Sharif Mamun, May 05 '14 at 19:49

score 4 · Answer 1 · answered May 05 '14 at 19:49

4

with open('myfile.txt') as f, open('myfile2.txt') as d:
    for line1, line2 in zip(f, d):
        do_something(line1, line2)

Note that, for Python 2, you should use itertools.izip - it only holds one pair of lines in memory at a time, rather than returning a list of all pairs of lines.

answered May 05 '14 at 19:49

Hugh Bothwell

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Will the `with` apply to the second file as well? – keyser May 05 '14 at 19:52
@keyser: yes, it will. – Hugh Bothwell May 05 '14 at 19:53
Yup, noticed it in the duplicate link above :) – keyser May 05 '14 at 19:53
Do I have the wrong syntax? I thought it was `with open('path/to/file1') as f_one and open('path/to/file2') as f_two`. Note that this only works in Python2.7+. Hmm I guess I do, as per the dupe listed by Dave Yarwood. Dang! – Adam Smith May 05 '14 at 19:53

How to iterate through 2 lists at once?

1 Answers1