Functional Programming In Python3.11+

example.py

from functional import Functional
import numpy as np

# Results in a NDArray[int_]
out = (
    Functional[str](["hei", "boo", "1", "2", "4"])
    .filter(lambda x: x.isnumeric())
    .map(lambda x: int(x))
    .enumerate()
    .map(lambda v: v[0] + v[1])
    .to(lambda x: np.fromiter(x, np.int_))
)

# Results in a list[int]
out = (
    Functional[str](["hei", "boo", "1", "2", "4"])
    .filter(lambda x: x.isnumeric())
    .map(lambda x: int(x))
    .enumerate()
    .map(lambda v: v[0] + v[1])
    .to_list()
)

functional.py

from typing import Callable, Generic, Iterable, TypeVar


T = TypeVar("T")
MapReturnValue = TypeVar("MapReturnValue")
ToReturnValue = TypeVar("ToReturnValue")


class Functional(Generic[T]):
    def __init__(self, gen: Iterable[T]) -> None:
        self.__gen = gen

    def enumerate(self):
        return Functional(enumerate(self.__gen))

    def map(self, function: Callable[[T], MapReturnValue]):
        gen = (function(v) for v in self.__gen)
        return Functional(gen)

    def filter(self, function: Callable[[T], bool]):
        gen = (v for v in self.__gen if function(v))
        return Functional(gen)

    def gen(self):
        return self.__gen

    def to(self, function: Callable[[Iterable[T]], ToReturnValue]):
        return function(self.__gen)

    def to_list(self):
        return list(self.__gen)

    def to_tuple(self):
        return tuple(self.__gen)