reduce vs non-reduce versions of Counter / frequencies

reimplement_counter.py

"""
finding use cases for "reduce" in python, attempt #2.

"reimplementing Counter()
cf https://docs.python.org/3/library/collections.html#collections.Counter
cf https://clojuredocs.org/clojure.core/frequencies 

"""

import functools
import typing

things = ["red", "blue", "red", "green", "blue", "blue"]
expected = {"red": 2, "blue": 3, "green": 1}


T = typing.TypeVar("T")


def counter_pythonic(l: list[T]) -> dict[T, int]:
    # um, this may be O(n²) 😅
    return {thing: l.count(thing) for thing in set(l)}


def counter_reduce(l: list[T]) -> dict[T, int]:
    return functools.reduce(
        lambda acc, x: acc | {x: acc.get(x, 0) + 1},
        l,
        {},
    )


def test_it_works_pythonic():
    assert counter_pythonic(things) == expected


def test_it_works_pythonic():
    assert counter_reduce(things) == expected