Is possible to iterate file by two lines? [duplicate]

Question

Possible Duplicate:
reading lines 2 at a time

In python we can iterate over file line by line. But what if i want iterate by two lines?

f = open("filename")
for line1, line2 in ?? f ??:
    do_stuff(line1, line2)

Answer 1

Use the grouper function from the itertools recipes.

from itertools import zip_longest

def grouper(n, iterable, fillvalue=None):
    "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return zip_longest(fillvalue=fillvalue, *args)


f = open(filename)
for line1, line2 in grouper(2, f):
    print('A:', line1, 'B:', line2)

Use zip instead of zip_longest to ignore an odd line at the end.

The zip_longest function was named izip_longest in Python 2.

Answer 2

You could do something like this:

with open('myFile.txt') as fh:
  for line1 in fh:
    line2 = next(fh)

    # Code here can use line1 and line2.

You may need to watch for a StopIteration error on the call to next(fh) if you have odd lines. The solutions with izip_longest are probably better able to avoid that need.