Groups consecutive number ranges together

group_ranges.py

import itertools

def group_ranges(L):
    """
    Collapses a list of integers into a list of the start and end of
    consecutive runs of numbers. Returns a generator of generators.

    >>> [list(x) for x in group_ranges([1, 2, 3, 5, 6, 8])]
    [[1, 3], [5, 6], [8]]
    """
    for w, z in itertools.groupby(L, lambda x, y=itertools.count(): next(y)-x):
        grouped = list(z)
        yield (x for x in [grouped[0], grouped[-1]][:len(grouped)])