Python实现扩展内置类型的方法分析

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。

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。

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。