Add groupsof built-in

[evhub]

Something like

def groupsof(n, iterable):
    """Split iterable into groups (tuples) of length n.
    If the length of iterable is not divisible by n, the last group may be of size < n."""
    iterator = iter(iterable)
    while True:
        group = [next(iterator)]
        for _ in range(1, n):
            try:
                group.append(next(iterator))
            except StopIteration:
                break
        yield tuple(group)
        if len(group) != n:
            break

[evhub]

Should probably be a class, though, not a function, like map, filter, enumerate, count, etc.

[kbaskett248]

I'm working on implementing this feature. I just need to finish up the tests and add documentation.

[evhub]

@kbaskett248 Awesome! Make sure you're working against develop, not master, then just submit a PR once you've got something you want me to take a look at!

[kbaskett248]

Sure thing. One question about the n argument: should I be validating it at all? Perhaps raise a TypeError if it can't be coerced to an int? Or maybe a ValueError if it is non-positive?

I implemented it using range like you suggested, so it does throw a TypeError when the __iter__ method is called. It might be better to check that in __init__ so the crash happens where the error is made.

You are free to pass in negative numbers or zero, however, which achieves the same results as passing in 1. This seems really unintuitive, so I think that may be worth raising an exception.

[evhub]

@kbaskett248 Raising an exception seems like a good idea, go for it! Also, just to check, you're putting this in header.py_template, correct?

[kbaskett248]

Yes, I am.