Group a list into chunks in Python WITHOUT removing smaller chunks

gistfile1.py

# source: http://countergram.com/python-group-iterator-list-function

def group_iter(iterator, n=2, strict=False):
    """ Transforms a sequence of values into a sequence of n-tuples.
    e.g. [1, 2, 3, 4, 5] => [(1, 2), (3, 4), (5,)] (when n == 2)
    If strict, then it will raise ValueError if there is a group of fewer
    than n items at the end of the sequence. """
    accumulator = []
    for item in iterator:
        accumulator.append(item)
        if len(accumulator) == n: # tested as fast as separate counter
            yield tuple(accumulator)
            accumulator = [] # tested faster than accumulator[:] = []
            # and tested as fast as re-using one list object
    if strict and len(accumulator) != 0:
        raise ValueError("Leftover values")
    else:
        yield tuple(accumulator)