What is the most "pythonic" way to iterate over a list in chunks?

Answer

Modified from the recipes section of Python's itertools docs:

def grouper(iterable, n, fillvalue=None):
    args =[iter(iterable)]* n
    return izip_longest(*args, fillvalue=fillvalue)

Example
In pseudocode to keep the example terse.

grouper('ABCDEFG',3,'x')-->'ABC''DEF''Gxx'