# mr.py

from functools import reduce

from typing import Callable, Iterable, TypeVar, Union, Optional

T = TypeVar('T')

S = TypeVar('S')

Number = Union[int, float]

print()

def map_reduce(

it: Iterable[T],

mapper: Callable[[T], S],

reducer: Callable[[S, S], S],

filterer: Optional[Callable[[S], bool]]

) -> S:

mapped = map(mapper, it)

filtered = filter(filterer, mapped)

reduced = reduce(reducer, filtered)

return reduced

def mapper(x: Number) -> Number:

return x ** 2

def filterer(x: Number) -> bool:

return x % 2 == 0

def reducer(x: Number, y: Number) -> Number:

return x + y

results = map_reduce(

range(10),

mapper=mapper,

reducer=reducer,

filterer=filterer

)

print(results)