Simple way to group items into buckets

Question

I often want to bucket an unordered collection in python. itertools.groubpy does the right sort of thing but almost always requires massaging to sort the items first and cat

Answer 1

This has come up several times before -- (1), (2), (3) -- and there's a partition recipe in the itertools recipes, but to my knowledge there's nothing in the standard library.. although I was surprised a few weeks ago by accumulate, so who knows what's lurking there these days? :^)

When I need this behaviour, I use

from collections import defaultdict

def partition(seq, key):
    d = defaultdict(list)
    for x in seq:
        d[key(x)].append(x)
    return d

and get on with my day.