python __filter__

#!/usr/bin/env python3
from abc import ABCMeta, abstractmethod
import random

#Filterable lets you use duck typing while still allowing use of isinstance
class Filterable(metaclass=ABCMeta):
    @classmethod
    def __subclasshook__(cls, C):
        if cls is Filterable:
            if hasattr(C, "__filter__"):
                return True
        return NotImplemented


def filter(function, sequence):
    if isinstance(sequence, Filterable):
        return sequence.__filter__(function)
    else:
        return __builtins__.filter(function, sequence)


class Items:
    def __init__(self, items):
        self.items = items

    def __filter__(self, function):
        ''' Insane version of filter that ignores the given function '''

        for item in self.items:
            if random.random() >= 0.5:
                yield item


if __name__ == "__main__":
    items = Items([1, 2, 3, 44, 32, 'a'])
    print(isinstance(items, Filterable))
    for item in filter(None, items):
        print(item)