Python抽象基类的定义与使用方法

import collections 
 
Card = collections.namedtuple('Card', ['rank', 'suit']) 
 
class FrenchDeck2(collections.MutableSequence): 
    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 __setitem__(self, position, value):  # <1> 
        self._cards[position] = value 
 
    def __delitem__(self, position):  # <2> 
        del self._cards[position] 
 
    def insert(self, position, value):  # <3> 
        self._cards.insert(position, value) 

# BEGIN TOMBOLA_ABC 
 
import abc 
 
class Tombola(abc.ABC):  # <1> 
 
    @abc.abstractmethod 
    def load(self, iterable):  # <2> 
        """Add items from an iterable.""" 
 
    @abc.abstractmethod 
    def pick(self):  # <3> 
        """Remove item at random, returning it. 
        This method should raise `LookupError` when the instance is empty. 
        """ 
 
    def loaded(self):  # <4> 
        """Return `True` if there's at least 1 item, `False` otherwise.""" 
        return bool(self.inspect())  # <5> 
 
 
    def inspect(self): 
        """Return a sorted tuple with the items currently inside.""" 
        items = [] 
        while True:  # <6> 
            try: 
                items.append(self.pick()) 
            except LookupError: 
                break 
        self.load(items)  # <7> 
        return tuple(sorted(items)) 
 
 
# END TOMBOLA_ABC 

Sequence.register(tuple) 
Sequence.register(str) 
Sequence.register(range) 
Sequence.register(memoryview) 

@Tombola.register 
class TomboList(list): 
    ...