python - 类对象不打印

Question

我的类对象不会在 Python 中打印。这是我的代码:

import random

suits = ("Hearts", "Diamonds", "Spades", "Clubs")
ranks = ("Two","Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King", "Ace")
values = {'Two':2, 'Three':3, 'Four':4, 'Five':5, 'Six':6, 'Seven':7, 'Eight':8, 'Nine':9, 'Ten':10, 'Jack':10,
         'Queen':10, 'King':10, 'Ace':11}

playing = True

class Card:

    def __init__(self, suit, rank):
        self.suit = suit
        self.rank = rank

    def __str__(self):
        return self.rank + " of " + self.suit

class Deck:

    def __init__(self):
        self.deck = []  # start with an empty list
        for suit in suits:
            for rank in ranks:
                self.deck.append(Card(suit,rank))

    def __str__(self):
        return self.deck

    def shuffle(self):
        random.shuffle(self.deck)

    def deal(self):
        pass

test_deck = Deck()
#len(test_deck.deck)
print(test_deck)

此代码的最后一行 print(test_deck) 给出了以下错误，我不知道为什么，因为我正在遵循使用 __str__ 进行打印的类似示例一个类对象:

    ---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
 in 
      1 test_deck = Deck()
      2 len(test_deck.deck)
----> 3 print(test_deck)

TypeError: __str__ returned non-string (type list)

我不知道为什么我无法打印列表？即使我使用了return

Answer 1

__str__方法必须返回字符串格式

你可以这样重写

def __str__(self):
    return ", ".join([str(card) for card in self.deck])

所以它会打印这样的内容

Two of Hearts, Five of Diamonds

或者如果你想显式地表明它是一个列表结构，只需返回 str(self.deck)

所以它会打印这样的内容

"[<__main__.Card object at 0x7f8ad5a1e190>, <__main__.Card object at 0x7f8ad5a1e190>]"