详解Python中的__new__()方法的使用

  class object: 
    @staticmethod # known case of __new__ 
    def __new__(cls, *more): # known special case of object.__new__ 
      """ T.__new__(S, ...) -> a new object with type S, a subtype of T """ 
      pass 

  class Demo(object): 
    def __init__(self): 
      print '__init__() called...' 
    def __new__(cls, *args, **kwargs): 
      print '__new__() - {cls}'.format(cls=cls) 
      return object.__new__(cls, *args, **kwargs) 
  if __name__ == '__main__': 
    de = Demo() 

  __new__() - <class '__main__.Demo'> 
  __init__() called... 

  class LxmlDocument(object_ref): 
    cache = weakref.WeakKeyDictionary() 
    __slots__ = ['__weakref__'] 
    def __new__(cls, response, parser=etree.HTMLParser): 
      cache = cls.cache.setdefault(response, {}) 
      if parser not in cache: 
        obj = object_ref.__new__(cls) 
        cache[parser] = _factory(response, parser) 
      return cache[parser]