实例变量

Question

class ShoppingCart: 

    def __init__(self): 
     self.cart = [] 

    def add_item(self, item): 
     """ (ShoppingCart, Item) -> NoneType 
     Adds an item to the cart. 
     """ 
     self.cart.append(item) 

    def show_cheapest_item(self): 
     """ (ShoppingCart) -> int 
     Return the cheapest item in the cart, or -1 if no items are in the cart 
     """ 
     # my point of confusion 

---

class Item: 

    """ An instance of an item """ 
    def __init__(self, price): 
     """ (Item, float) 
     Initialize an Item 
     """ 
     self.price = price 

我想在车返回最廉价的物品内发现的最低值，我无法访问任何方式价目表。

Answer 1

def show_cheapest_item(self): 
    """ (ShoppingCart) -> int 
    Return the cheapest item in the cart, or -1 if no items are in the cart 
    """ 
    if len(self.cart) == 0: 
     return -1 
    cheapest_item = self.cart[0] 
    for item in self.cart[1:]: 
     if item.price < cheapest_item.price: 
      cheapest_item = item 
    return cheapest_item 

Answer 2

class ShoppingCart: 

    def __init__(self): 
     self.cart = [] 

    def add_item(self, item): 
     """ (ShoppingCart, Item) -> NoneType 
     Adds an item to the cart. 
     """ 
     self.cart.append(item) 

    def show_cheapest_item(self): 
     """ (ShoppingCart) -> int 
     Return the cheapest item in the cart, or -1 if no items are in the cart 
     """ 
     return -1 if len(self.cart) == 0 else min(self.cart) 

Answer 3

使用min和operator.attrgetter

import operator 

def show_cheapest_item(self): 
    """ (ShoppingCart) -> int 
    Return the cheapest item in the cart, or -1 if no items are in the cart 
    """ 
    return -1 if not self.cart else min(self.cart, key=operator.attrgetter('price'))