ShoppingCart.py

class ShoppingCart(object):
  def __init__(self):
       self.total = 0
       self.items = {}

  def add_item(self, item_name, quantity, price):
       self.total += price*quantity
       self.items.update({item_name: quantity})

  def remove_item(self, item_name, quantity, price):
        if quantity >= self.items[item_name] and quantity >= 1:
            items_cost = price * self.items[item_name]
            self.total -= items_cost
            del self.items[item_name]
        else:
            self.total -= quantity * price
            self.items[item_name] -= quantity


  def checkout (self, cash_paid):
       if cash_paid >= self.total:
           return cash_paid - self.total
       return "Cash paid not enough"

class Shop(ShoppingCart):

     def __init__(self):
         self.quantity = 100

     def remove_item(self):
         self.quantity -=1