1. 序列__getitem__
如果没有 __iter__ 和 __contains__ 方法，
python 会调用 __getitem__ 方法，
设法让 迭代 和 in 运算符可用
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class foo: def __getitem__(self, pos): return range(0, 30, 10)[pos]f = foo()print(f[1]) # 10for i in f: print(i) # 0, 10, 20# 如果没有 __iter__ 和 __contains__ 方法，# python 会调用 __getitem__ 方法，# 设法让迭代和 in 运算符可用 |
2. __setitem__
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import collectionscard = collections.namedtuple('card', ['rank', 'suit'])class frenchdeck: ranks = [str(n) for n in range(2, 11)] + list('jqka') suits = 'spades diamonds clubs hearts'.split() def __init__(self): self._cards = [card(rank, suit) for suit in self.suits for rank in self.ranks] def __len__(self): return len(self._cards) def __getitem__(self, position): return self._cards[position] def __str__(self): return ",".join(str(i) for i in self._cards)from random import shuffledeck = frenchdeck()print(str(deck))# card(rank='2', suit='spades'),card(rank='3', suit='spades'),card(rank='4', suit='spades'),card(rank='5', suit='spades'),card(rank='6', suit='spades'),card(rank='7', suit='spades'),card(rank='8', suit='spades'),card(rank='9', suit='spades'),card(rank='10', suit='spades'),card(rank='j', suit='spades'),card(rank='q', suit='spades'),card(rank='k', suit='spades'),card(rank='a', suit='spades'),card(rank='2', suit='diamonds'),card(rank='3', suit='diamonds'),card(rank='4', suit='diamonds'),card(rank='5', suit='diamonds'),card(rank='6', suit='diamonds'),card(rank='7', suit='diamonds'),card(rank='8', suit='diamonds'),card(rank='9', suit='diamonds'),card(rank='10', suit='diamonds'),card(rank='j', suit='diamonds'),card(rank='q', suit='diamonds'),card(rank='k', suit='diamonds'),card(rank='a', suit='diamonds'),card(rank='2', suit='clubs'),card(rank='3', suit='clubs'),card(rank='4', suit='clubs'),card(rank='5', suit='clubs'),card(rank='6', suit='clubs'),card(rank='7', suit='clubs'),card(rank='8', suit='clubs'),card(rank='9', suit='clubs'),card(rank='10', suit='clubs'),card(rank='j', suit='clubs'),card(rank='q', suit='clubs'),card(rank='k', suit='clubs'),card(rank='a', suit='clubs'),card(rank='2', suit='hearts'),card(rank='3', suit='hearts'),card(rank='4', suit='hearts'),card(rank='5', suit='hearts'),card(rank='6', suit='hearts'),card(rank='7', suit='hearts'),card(rank='8', suit='hearts'),card(rank='9', suit='hearts'),card(rank='10', suit='hearts'),card(rank='j', suit='hearts'),card(rank='q', suit='hearts'),card(rank='k', suit='hearts'),card(rank='a', suit='hearts')shuffle(deck) # typeerror: 'frenchdeck' object does not support item assignment |
加入__setitem__
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def __setitem__(self, key, value): self._cards[key] = value |
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shuffle(deck) print(str(deck))# 牌被随机打乱了# card(rank='6', suit='hearts'),card(rank='2', suit='spades'),card(rank='3', suit='hearts'),card(rank='a', suit='clubs'),card(rank='7', suit='clubs'),card(rank='q', suit='diamonds'),card(rank='5', suit='hearts'),card(rank='6', suit='spades'),card(rank='5', suit='diamonds'),card(rank='8', suit='diamonds'),card(rank='k', suit='hearts'),card(rank='q', suit='hearts'),card(rank='8', suit='hearts'),card(rank='3', suit='diamonds'),card(rank='q', suit='clubs'),card(rank='a', suit='diamonds'),card(rank='9', suit='hearts'),card(rank='7', suit='diamonds'),card(rank='a', suit='spades'),card(rank='j', suit='hearts'),card(rank='3', suit='clubs'),card(rank='4', suit='hearts'),card(rank='q', suit='spades'),card(rank='10', suit='diamonds'),card(rank='10', suit='hearts'),card(rank='k', suit='diamonds'),card(rank='2', suit='diamonds'),card(rank='4', suit='spades'),card(rank='3', suit='spades'),card(rank='7', suit='hearts'),card(rank='9', suit='clubs'),card(rank='j', suit='clubs'),card(rank='j', suit='diamonds'),card(rank='10', suit='spades'),card(rank='4', suit='diamonds'),card(rank='7', suit='spades'),card(rank='9', suit='diamonds'),card(rank='2', suit='hearts'),card(rank='6', suit='clubs'),card(rank='k', suit='clubs'),card(rank='4', suit='clubs'),card(rank='a', suit='hearts'),card(rank='k', suit='spades'),card(rank='2', suit='clubs'),card(rank='j', suit='spades'),card(rank='8', suit='spades'),card(rank='5', suit='spades'),card(rank='9', suit='spades'),card(rank='10', suit='clubs'),card(rank='8', suit='clubs'),card(rank='6', suit='diamonds'),card(rank='5', suit='clubs') |
或者 在类外打补丁 frenchdeck.__setitem__ = 函数
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def set_card(deck, position, card): deck._cards[position] = cardfrenchdeck.__setitem__ = set_card |
3. 抽象基类
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class test: def __len__(self): return 24from collections import abcprint(isinstance(test(), abc.sized)) # true |
只要实现了 __len__() 方法，就可以被 abc.sized 识别为子类
4. 不要直接子类化内置类型
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class answerdict(dict): def __getitem__(self, key): return 24ad = answerdict(a="good")print(ad['a']) # 24d = {}d.update(ad)print(d['a']) # goodprint(ad) # {'a': 'good'}print(d) # {'a': 'good'} |
直接子类化内置类型（如 dict、list 或 str）容易出错， 因为 内置类型的方法 通常会 忽略用户覆盖的方法。
不要子类化内置 类型，用户自己定义的类 应该继承 collections 模块 中的类，例如 userdict、userlist 和 userstring，这些类做了特殊设计，因 此易于扩展
5. 继承顺序
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import collectionsclass answerdict2(collections.userdict): def __getitem__(self, key): return 24ad = answerdict2(a="good")print(ad['a']) # 24d = {}d.update(ad)print(d['a']) # 24print(ad) # {'a': 'good'}print(d) # {'a': 24} |
- 多重继承的同名方法调用，根据类的 __mro__ 属性顺次在类中查找
- 推荐使用 super() 函数
6. 重载运算符
不可变类型，，一定不能实现就地特殊方法
__iadd__等增量赋值特殊方法 必须返回 self
总结
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原文链接：https://blog.csdn.net/qq_21201267/article/details/119203009
