120 – All equal

To check if all values of an iterable are equal (up to a key function), you can use itertools.groupby and check how many groups are found (under the same key function):

from itertools import groupby, islice

def take(iterable, n):
    return list(islice(iterable, n))

def all_equal(iterable, *, key=None):
    return len(take(
        groupby(iterable, key),
        2,
    )) <= 1

The function all_equal uses groupby to create runs of elements that are the same under the function key. Then, the function take is used to try and take the first 2 of those runs. If there are no runs, or if there is only one run, it’s because all values were the same.