Iterate over a string 2 (or n) characters at a time in Python

Question

Earlier today I needed to iterate over a string 2 characters at a time for parsing a string formatted like \"+c-R+D-E\" (there are a few extra letters).

Answer 1

This approach support an arbitrary number of elements per result, evaluates lazily, and the input iterable can be a generator (no indexing is attempted):

import itertools

def groups_of_n(n, iterable):
    c = itertools.count()
    for _, gen in itertools.groupby(iterable, lambda x: c.next() / n):
        yield gen

Any left-over elements are returned in a shorter list.

Example usage:

for g in groups_of_n(4, xrange(21)):
    print list(g)

[0, 1, 2, 3]
[4, 5, 6, 7]
[8, 9, 10, 11]
[12, 13, 14, 15]
[16, 17, 18, 19]
[20]