Using OOP, a simple calculator is created which keeps track of previous operations.

Class Calculator

class Calculator(object):
    def __init__(self):
        self.cache = {}
        
    def add(self, x, y):
        if not self.cache.has_key('add'):
            self.cache.setdefault('add', [])
        for previous_x, previous_y, res in self.cache['add']:
            if previous_x == x and previous_y == y:
                return res 
        else:
            self.cache['add'].append((x, y, x+y))
            return x+y
    
    def subtract(self, x, y):
        if not self.cache.has_key('subtract'):
            self.cache.setdefault('subtract', [])
        for previous_x, previous_y, res in self.cache['subtract']:
            if previous_x == x and previous_y == y:
                return res
        else:
            self.cache['subtract'].append((x, y, x-y))
            return x-y
            
    def multiply (self, x, y):
        if not self.cache.has_key('multiply'):
            self.cache.setdefault('multiply', [])
        for previous_x, previous_y, res in self.cache['multiply']:
            if previous_x == x and previous_y == y:
                return res 
        else:
            self.cache['multiply'].append((x, y, x*y))
            return x*y
    
    def divide (self, x, y):
        if not self.cache.has_key('divide'):
            self.cache.setdefault('divide', [])
        for previous_x, previous_y, res in self.cache['divide']:
            if previous_x == x and previous_y == y:
                return res 
        else:
            self.cache['divide'].append((x, y, x/y))
            return x/y