本文实例讲述了Python实现扩展内置类型的方法。分享给大家供大家参考，具体如下：
简介
除了实现新的类型的对象方式外，有时我们也可以通过扩展Python内置类型，从而支持其它类型的数据结构，比如为列表增加队列的插入和删除的方法。本文针对此问题，结合实现集合功能的实例，介绍了扩展Python内置类型的两种方法：通过嵌入内置类型来扩展类型和通过子类方式扩展类型。
通过嵌入内置类型扩展
下面例子通过将list对象作为嵌入类型，实现集合对象，并增加了一下运算符重载。这个类知识包装了Python的列表，以及附加的集合运算。
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class Set: def __init__(self, value=[]): # Constructor self.data = [] # Manages a list self.concat(value) def intersect(self, other): # other is any sequence res = [] # self is the subject for x in self.data: if x in other: # Pick common items res.append(x) return Set(res) # Return a new Set def union(self, other): # other is any sequence res = self.data[:] # Copy of my list for x in other: # Add items in other if not x in res: res.append(x) return Set(res) def concat(self, value): # value: list, Set... for x in value: # Removes duplicates if not x in self.data: self.data.append(x) def __len__(self): return len(self.data) # len(self) def __getitem__(self, key): return self.data[key] # self[i] def __and__(self, other): return self.intersect(other) # self & other def __or__(self, other): return self.union(other) # self | other def __repr__(self): return 'Set:' + repr(self.data) # print()if __name__ == '__main__': x = Set([1, 3, 5, 7]) print(x.union(Set([1, 4, 7]))) # prints Set:[1, 3, 5, 7, 4] print(x | Set([1, 4, 6])) # prints Set:[1, 3, 5, 7, 4, 6] |
通过子类方式扩展类型
从Python2.2开始，所有内置类型都能直接创建子类，如list，str，dict以及tuple。这样可以让你通过用户定义的class语句，定制或扩展内置类型：建立类型名称的子类并对其进行定制。类型的子类型实例，可用在原始的内置类型能够出现的任何地方。
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class Set(list): def __init__(self, value = []): # Constructor list.__init__([]) # Customizes list self.concat(value) # Copies mutable defaults def intersect(self, other): # other is any sequence res = [] # self is the subject for x in self: if x in other: # Pick common items res.append(x) return Set(res) # Return a new Set def union(self, other): # other is any sequence res = Set(self) # Copy me and my list res.concat(other) return res def concat(self, value): # value: list, Set . . . for x in value: # Removes duplicates if not x in self: self.append(x) def __and__(self, other): return self.intersect(other) def __or__(self, other): return self.union(other) def __repr__(self): return 'Set:' + list.__repr__(self)if __name__ == '__main__': x = Set([1,3,5,7]) y = Set([2,1,4,5,6]) print(x, y, len(x)) print(x.intersect(y), y.union(x)) print(x & y, x | y) x.reverse(); print(x) |
希望本文所述对大家Python程序设计有所帮助。
原文链接：http://blog.csdn.net/jinguangliu/article/details/44240171
