Iterating over 3 lines at a time (for stdout) in Python

iterate_n_lines.py

import subprocess
import itertools

# execute some command 
since = "--since='{0}-{1}-1'".format(str(year), str(month))
until = "--before='{0}-{1}-{2}'".format(str(year), str(month), str(days_in_month[month-1]))
args = ['git', 'log', '--pretty=format:"%ai %aE"', '--shortstat', since, until]
sub = subprocess.Popen(args, stdout=subprocess.PIPE, close_fds=True, cwd='/path/to/git/repo/clone')

for line1,line2,line3 in itertools.izip_longest(*[sub.stdout]*3):
    # Do stuff with line1, line2, line3...