Method groupby

Lib/test/test_itertools.py:1665–1695

(iterable, key=None)

        # Begin groupby() recipe #######################################

        def groupby(iterable, key=None):
            # [k for k, g in groupby('AAAABBBCCDAABBB')] → A B C D A B
            # [list(g) for k, g in groupby('AAAABBBCCD')] → AAAA BBB CC D

            keyfunc = (lambda x: x) if key is None else key
            iterator = iter(iterable)
            exhausted = False

            def _grouper(target_key):
                nonlocal curr_value, curr_key, exhausted
                yield curr_value
                for curr_value in iterator:
                    curr_key = keyfunc(curr_value)
                    if curr_key != target_key:
                        return
                    yield curr_value
                exhausted = True

            try:
                curr_value = next(iterator)
            except StopIteration:
                return
            curr_key = keyfunc(curr_value)

            while not exhausted:
                target_key = curr_key
                curr_group = _grouper(target_key)
                yield curr_key, curr_group
                if curr_key == target_key:
                    for _ in curr_group:
                        pass

        # End groupby() recipe #########################################