Python扩展内置类型的实现方法分析

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]

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)