proxy.py

# -*- coding: utf-8 -*-

"""
Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed. 
    This pattern appears in the GoF catalog as "virtual proxy", an implementation strategy for the Proxy pattern.
"""

class IMath:
    """Interface for proxy and real subject."""
    def add(self, x, y):
        raise NotImplementedError()

    def sub(self, x, y):
        raise NotImplementedError()

    def mul(self, x, y):
        raise NotImplementedError()

    def div(self, x, y):
        raise NotImplementedError()

class Math(IMath):
    """Real subject."""
    def add(self, x, y):
        return x + y

    def sub(self, x, y):
        return x - y

    def mul(self, x, y):
        return x * y

    def div(self, x, y):
        return x / y

class Proxy(IMath):
    """Proxy."""
    def __init__(self):
        self.math = Math()

    def add(self, x, y):
        return self.math.add(x, y)

    def sub(self, x, y):
        return self.math.sub(x, y)

    def mul(self, x, y):
        return self.math.mul(x, y)

    def div(self, x, y):
        if y == 0:
            return float('inf') # Вернуть positive infinity
        return self.math.div(x, y)

p = Proxy()
x, y = 4, 2
print '4 + 2 = ' + str(p.add(x, y))
print '4 - 2 = ' + str(p.sub(x, y))
print '4 * 2 = ' + str(p.mul(x, y))
print '4 / 2 = ' + str(p.div(x, y))