grouping pairs using itertools

group_pairs.py

from itertools import groupby
from operator import itemgetter


def group_pairs(iterable):
    """Given a sorted list of pairs, group by the first element in
    each pair.

    >>> group_pairs([('a', 1), ('a', 2), ('b', 3)])
    [('a', [1, 2]), ('b', [3])]

    """
    for key, group in groupby(iterable, itemgetter(0)):
        yield (key, map(itemgetter(1), group))