Python子类从父类调用方法

Question

我目前正在自学 Python，并且上过关于继承的课程，所以这是我第一次接触子类。我正在从“Think Python”一书中学习，这个例子是关于创建代表扑克牌、甲板、手牌等的类。下面的例子是从这本书中复制的（我自己添加了一个或两个方法，作为练习）：

import random
from operator import itemgetter, attrgetter

class Card:
"""represents a standard playing card."""
    def __init__(self, suit=0, rank=2):
        self.suit = suit
        self.rank = rank

    suit_names = ['Clubs', 'Diamonds', 'Hearts', 'Spades']
    rank_names = [None, 'Ace', '2', '3', '4', '5', '6', '7', '8', '9', '10', 'Jack', 'Queen', 'King']

    def __str__(self):
        return '%s of %s' % (Card.rank_names[self.rank], Card.suit_names[self.suit])

    def __cmp__(self, other):
        t1 = self.suit, self.rank
        t2 = other.suit, other.rank
        return cmp(t1, t2)

class Deck:
"""represents a standard deck of cards"""
    def __init__(self):
        self.cards = []
        for suit in range(4):
            for rank in range(1, 14):
                card = Card(suit, rank)
                self.cards.append(card)

    def __str__(self):
        res = []
        for card in self.cards:
            res.append(str(card))
        return '\n'.join(res)

    def pop_card(self):
        return self.cards.pop()

    def add_card(self):
        self.cards.append(card)

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

    def sort(self):
        self.cards.sort(key=attrgetter('suit', 'rank'))

class Hand(Deck):
"""represents a hand of playing cards"""
    def __init__(self, label=''):
        self.cards = []
        self.label = label

    def move_cards(self, hand, num):
        for i in range(num):
            hand.add_card(self.pop_card())

我的问题是 Hand 子类方法。如果我尝试从 Hand 子类调用 move_cards 方法，例如使用a = Deck()、b = Hand()，尝试调用move_cards(b,2) 或a.move_cards(b,2) 给我同样的AttributeError: 'Deck' object has no attribute 'move_cards'。

为什么会发生这种情况或我做错了什么？谢谢。

Answer 1

move_cards 只为子类Hand 定义，而不是父类Deck。

我认为示例中的继承顺序令人困惑 - Hand 并不真的是 Deck 的子类，而是它们都应该是公共卡片集合的子类（Stack 说）。例如（未测试）：

class Stack:
"""represents a collection of cards"""
    def __init__(self):
        self.cards = []

    def __str__(self):
        res = []
        for card in self.cards:
            res.append(str(card))
        return '\n'.join(res)

    def pop_card(self):
        return self.cards.pop()

    def add_card(self):
        self.cards.append(card)

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

    def sort(self):
        self.cards.sort(key=attrgetter('suit', 'rank'))

    def move_cards(self, dest, num):
        for i in range(num):
            dest.add_card(self.pop_card())

class Deck(Stack):
"""represents a deck of playing cards"""
    def __init__(self):
        Stack.__init__(self)
        for suit in range(4):
            for rank in range(1, 14):
                card = Card(suit, rank)
                self.cards.append(card)

class Hand(Stack):
"""represents a hand of playing cards"""
    def __init__(self, label=''):
        Stack.__init__(self)
        self.label = label

注意子类Hand 和Deck 的重写构造函数如何使用Stack.__init__(self) 显式调用父构造函数。这将以相同的方式为每个成员初始化 self.cards 成员。