Automatic partially-applied binary operators ala Haskell, for Python

comp.py

class Comparator():
    """Support 'partial binding' of built in operators."""
    def __call__(self, a):
        """For support of nested PendingOperations, comparator(a) == a"""
        return a

    # A bunch of boring operators
    def __lt__(self, b):
        return PendingOperation(lambda a: self(a) < b)

    def __gt__(self, b):
        return PendingOperation(lambda a: self(a) > b)

    def __eq__(self, b):
        return PendingOperation(lambda a: self(a) == b)

    def __mod__(self, b):
        return PendingOperation(lambda a: self(a) % b)

    def __and__(self, b):
        return PendingOperation(lambda a: self(a) & b)

    def __or__(self, b):
        return PendingOperation(lambda a: self(a) | b)

    def __add__(self, b):
        return PendingOperation(lambda a: self(a) + b)

    def __sub__(self, b):
        return PendingOperation(lambda a: self(a) - b)

    def __mult__(self, b):
        return PendingOperation(lambda a: self(a) * b)

    def __truediv__(self, b):
        return PendingOperation(lambda a: self(a) / b)

    def __floordiv__(self, b):
        return PendingOperation(lambda a: self(a) // b)

    def __getitem__(self, key):
        return PendingOperation(lambda a: self(a)[key])

    def __getattr__(self, attr):
        return PendingOperation(lambda a: getattr(self(a), attr))


class PendingOperation(Comparator):
    """Support for chainable partially bound functions"""
    def __init__(self, fn):
        self.fn = fn

    def __call__(self, value):
        value = self.fn(value)
        return value


# Various aliases for a comparator instance. Pick one you like
_ = x = thing = item = Comparator()


def test():
    """Put the comparator through its paces"""
    assert (thing < 10)(5)
    assert (thing > 10)(15)

    assert list(filter(_ < 5, range(10))) == [0, 1, 2, 3, 4]
    assert list(filter(x % 2 == 0, range(10))) == [0, 2, 4, 6, 8]
    assert (x['hello'])({'hello': 'world'}) == 'world'

    print("All good!")


if __name__ == '__main__':
    test()