gistfile1.txt

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

class IMath:
    """Interface for proxy and real object"""
    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):
    """Реальный субъект"""
    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 = None

    def add(self, x, y):
        return x + y

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

    def mul(self, x, y):
        if not self.math:
            self.math = Math()
        return self.math.mul(x, y)

    def div(self, x, y):
        if y == 0:
            return float('inf')
        if not self.math:
            self.math = Math()
        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))