A maybe (?Monad)

maybe.py

import random


class Maybe:

    def __init__(self, item=None):
        self._item = item

    def __iter__(self):
        if self._item is not None:
            yield self._item

    def __len__(self):
        return int(self._item is not None)

    def map(self, f):
        if self._item is not None:
            return Maybe(f(self._item))
        return Maybe()

    def __repr__(self):
        if self._item is not None:
            return repr(self._item)
        return None


def double(x):
    return 2*x


def triple(x):
    return 3*x


def just(item):
    return Maybe(item)

def nothing():
    return Maybe()



thing = random.choice(
    [
        just(5),
        nothing(),
    ]
)


m = thing.map(double).map(triple)

for item in m:
    print(item)