groupby_unsorted.py

from collections import OrderedDict

def groupby_unsorted(iterable, key=None):
    '''
    An implementation of itertools.groupby which eager evaluates groups and
    therefore does not require its iterable to be pre-sorted. Groups are
    returned in the order they are seen.
    '''
    key = key or (lambda x: x)
    groups = OrderedDict()
    for item in iterable:
        item_key = key(item)
        if item_key not in groups:
            groups[item_key] = []
        groups[item_key].append(item)
    return groups.items()