Recursive reduce implementation with test

reduce_implementation.py

#! /usr/bin/env python3

def reduce2(func, ls):
    if len(ls) == 1:
        return ls[0]
    return func(reduce2(func, ls[:-1]), ls[-1])


# test
testset = [1, 2, 3, 4, 5]

summation = reduce2(lambda a, x: a + x, testset)
subtr = reduce2(lambda a, x: a - x, testset)
assert summation == 15
assert subtr == -13

# compare against functools reduce
from functools import reduce
assert summation == reduce(lambda a, x: a + x, testset)
assert subtr == reduce(lambda a, x: a - x, testset)