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

Here's a variant of partition() from above when the predicate is boolean, avoiding the cost of a dict/defaultdict:

def boolpartition(seq, pred):
    passing, failing = [], []
    for item in seq:
        (passing if pred(item) else failing).append(item)
    return passing, failing

Example usage:

>>> even, odd = boolpartition([1, 2, 3, 4, 5], lambda x: x % 2 == 0)
>>> even
[2, 4]
>>> odd
[1, 3, 5]