在列表中添加/移除项目

Question

我正在尝试创建一个玩家，可以在他们的背包里添加和删除物品。我已经把大部分功能都搞定了，只是遇到了一个小问题。每次打印背包的时候，都会出现一个'None'。我一直在尝试去掉它，但无论我怎么做，'None'总是出现在程序里！我知道我只是漏掉了什么简单的东西，但我就是搞不明白。

class Player(object):

  def __init__(self, name, max_items, items):
    self.name=name
    self.max_items=max_items
    self.items=items

  def inventory(self):
    for item in self.items:
        print item

  def take(self, new_item):
    if len(self.items)<self.max_items:
        self.items.append(new_item)
    else:
        print "You can't carry any more items!"

  def drop(self, old_item):
    if old_item in self.items:
        self.items.remove(old_item)
    else:
        print "You don't have that item."


def main():
  player=Player("Jimmy", 5, ['sword', 'shield', 'ax'])
  print "Max items:", player.max_items
  print "Inventory:", player.inventory()

  choice=None
  while choice!="0":
    print \
    """
    Inventory Man

    0 - Quit
    1 - Add an item to inventory
    2 - Remove an item from inventory
    """

    choice=raw_input("Choice: ")
    print

    if choice=="0":
        print "Good-bye."

    elif choice=="1":
        new_item=raw_input("What item would you like to add to your inventory?")
        player.take(new_item)
        print "Inventory:", player.inventory()

    elif choice=="2":
        old_item=raw_input("What item would you like to remove from your inventory?")
        player.drop(old_item)
        print "Inventory:", player.inventory()


    else:
        print "\nSorry, but", choice, "isn't a valid choice."

main()

raw_input("Press enter to exit.")

Answer 1

你能把这个函数替换成下面这个吗：

def inventory(self):
  for item in self.items:
      print item

然后再调用：

def inventory(self):
    print self.items

或者你也可以使用这个函数：

print "Inventory"
player.inventory()

：

def print_inventory(self):
    print "Inventory:"
    for item in self.items:
        print item

Answer 2

问题出在这句话上：

print "Inventory:", player.inventory()

你让Python打印从player.inventory()得到的值。但是你的inventory()方法只是打印库存内容，并没有返回任何东西，所以它的返回值实际上是None。

你可能想要明确选择以下两种方式之一：

print "Inventory:"
player.print_inventory()

或者你也可以让它返回一个字符串，然后这样做：

print "Inventory:", player.inventory_as_str()