specification.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
*TL;DR
Provides recombination business logic by chaining together using boolean logic.
"""

from abc import abstractmethod


class Specification(object):

    @abstractmethod
    def is_satisfied_by(self, candidate):
        pass


class SpecificationChain(Specification):
    def is_satisfied_by(self, candidate):
        return True  # identity comparison

    def __and__(self, candidate):
        return AndSpecification(self, candidate)

    def __or__(self, candidate):
        return OrSpecification(self, candidate)

    def __inv__(self):
        return NotSpecification(self)


class AndSpecification(SpecificationChain):
    _one = Specification()
    _other = Specification()

    def __init__(self, one, other):
        self._one = one
        self._other = other

    def is_satisfied_by(self, candidate):
        return bool(self._one.is_satisfied_by(candidate) and self._other.is_satisfied_by(candidate))


class OrSpecification(SpecificationChain):
    _one = Specification()
    _other = Specification()

    def __init__(self, one, other):
        self._one = one
        self._other = other

    def is_satisfied_by(self, candidate):
        return bool(self._one.is_satisfied_by(candidate) or self._other.is_satisfied_by(candidate))


class NotSpecification(SpecificationChain):
    _wrapped = Specification()

    def __init__(self, wrapped):
        self._wrapped = wrapped

    def is_satisfied_by(self, candidate):
        return bool(not self._wrapped.is_satisfied_by(candidate))


class User(object):
    def __init__(self, super_user=False):
        self.super_user = super_user


class UserSpecification(Specification):
    def is_satisfied_by(self, candidate):
        return isinstance(candidate, User)


class SuperUserSpecification(Specification):
    def is_satisfied_by(self, candidate):
        return getattr(candidate, 'super_user', False)


def main():
    print('Specification')
    andrey = User()
    ivan = User(super_user=True)
    vasiliy = 'not User instance'

    root_specification = SpecificationChain() & UserSpecification() & SuperUserSpecification()

    print(root_specification.is_satisfied_by(andrey))
    print(root_specification.is_satisfied_by(ivan))
    print(root_specification.is_satisfied_by(vasiliy))


if __name__ == '__main__':
    main()


OUTPUT = """
Specification
False
True
False
"""