In Python, how do I iterate over one iterator and then another?

Question

I'd like to iterate two different iterators, something like this:

file1 = open('file1', 'r') file2 = open('file2', 'r') for item in one_then_another(file1, file2):     print item 

Which I'd expect to print all the lines of file1, then all the lines of file2.

I'd like something generic, as the iterators might not be files, this is just an example. I know I could do this with:

for item in [file1]+[file2]: 

but this reads both files into memory, which I'd prefer to avoid.

Answer 1

Use itertools.chain:

from itertools import chain for line in chain(file1, file2):    pass 

fileinput module also provides a similar feature:

import fileinput for line in fileinput.input(['file1', 'file2']):    pass