I frequently find myself doing the following for lists, sets, and dicts.

````
passes = [x for x in seq if cond(x)]
fails = [x for x in seq if not cond(x)]
````

The proposed function would behave similarly to `filter`, but it would return a tuple of the passes iterable and fails iterable rather than just the passes.

````
my_list = [-3, -2, -1, 0, 1, 2, 3]
def is_positive(n):
    return n > 0

positives, negatives = separate(function=is_positive, iterable=my_list)
````