Predicate Algebra in Python

class Predicate:
    """
    Define predicate algebra.

    >>> isEven=Predicate(lambda x: x % 2 == 0)
    >>> isOdd=Predicate(lambda x: x % 2 == 1)
    >>> isEven(6)
    True
    >>> isOdd(6)
    False

    >>> isEmpty=Predicate(lambda s: s == "")
    >>> isNotEmpty=~isEmpty
    >>> isEmpty("c")
    False
    >>> isNotEmpty("")
    False
    >>> isNotEmpty("hello")
    True
    """
    def __init__(self, predicate):
        self.predicate = predicate

    def __or__(self, other):
        return Predicate(lambda x: self.predicate(x) or other(x))

    def __and__(self, other):
        return Predicate(lambda x: self.predicate(x) and other(x))

    def __xor__(self, other):
        return Predicate(lambda x: self.predicate(x) ^ other(x))

    def __invert__(self):
        return Predicate(lambda x: not self.predicate(x))

    def __call__(self, x):
        return self.predicate(x)

if __name__ == "__main__":
    import doctest
    doctest.testmod()