Python object类中的特殊方法代码讲解

class object:
 """ The most base type """

 # del obj.xxx或delattr(obj,'xxx')时被调用，删除对象中的一个属性
 def __delattr__(self, *args, **kwargs): # real signature unknown
 """ Implement delattr(self, name). """
 pass

 # 对应dir(obj)，返回一个列表，其中包含所有属性和方法名（包含特殊方法）
 def __dir__(self, *args, **kwargs): # real signature unknown
 """ Default dir() implementation. """
 pass

 # 判断是否相等 equal ，在obj==other时调用。如果重写了__eq__方法，则会将__hash__方法置为None
 def __eq__(self, *args, **kwargs): # real signature unknown
 """ Return self==value. """
 pass

 # format(obj)是调用，实现如何格式化obj对象为字符串
 def __format__(self, *args, **kwargs): # real signature unknown
 """ Default object formatter. """
 pass

 # getattr(obj,'xxx')、obj.xxx时都会被调用，当属性存在时，返回值，不存在时报错（除非重写__getattr__方法来处理）。
 # 另外，hasattr(obj,'xxx')时也会被调用（估计内部执行了getattr方法）
 def __getattribute__(self, *args, **kwargs): # real signature unknown
 """ Return getattr(self, name). """
 pass

 # 判断是否大于等于 greater than or equal，在obj>=other时调用
 def __ge__(self, *args, **kwargs): # real signature unknown
 """ Return self>=value. """
 pass

 # 判断是否大于 greater than，在obj>other时调用
 def __gt__(self, *args, **kwargs): # real signature unknown
 """ Return self>value. """
 pass

 # 调用hash(obj)获取对象的hash值时调用
 def __hash__(self, *args, **kwargs): # real signature unknown
 """ Return hash(self). """
 pass

 def __init_subclass__(self, *args, **kwargs): # real signature unknown
 """
 This method is called when a class is subclassed.

 The default implementation does nothing. It may be
 overridden to extend subclasses.
 """
 pass

 # object构造函数，当子类没有构造函数时，会调用object的__init__构造函数
 def __init__(self): # known special case of object.__init__
 """ Initialize self. See help(type(self)) for accurate signature. """
 pass

 # 判断是否小于等于 less than or equal，在obj<=other时调用
 def __le__(self, *args, **kwargs): # real signature unknown
 """ Return self<=value. """
 pass

 # 判断是否小于 less than，在obj<other时调用
 def __lt__(self, *args, **kwargs): # real signature unknown
 """ Return self<value. """
 pass

 # 创建一个cls类的对象，并返回
 @staticmethod # known case of __new__
 def __new__(cls, *more): # known special case of object.__new__
 """ Create and return a new object. See help(type) for accurate signature. """
 pass

 # 判断是否不等于 not equal,在obj!=other时调用
 def __ne__(self, *args, **kwargs): # real signature unknown
 """ Return self!=value. """
 pass

 def __reduce_ex__(self, *args, **kwargs): # real signature unknown
 """ Helper for pickle. """
 pass

 def __reduce__(self, *args, **kwargs): # real signature unknown
 """ Helper for pickle. """
 pass

 # 如果不重写__str__，则__repr__负责print(obj)和交互式命令行中输出obj的信息
 # 如果重写了__str__，则__repr__只负责交互式命令行中输出obj的信息
 def __repr__(self, *args, **kwargs): # real signature unknown
 """ Return repr(self). """
 pass

 # 使用setattr(obj,'xxx',value)、obj.xxx=value是被调用（注意，构造函数初始化属性也要调用）
 def __setattr__(self, *args, **kwargs): # real signature unknown
 """ Implement setattr(self, name, value). """
 pass

 # 获取对象内存大小
 def __sizeof__(self, *args, **kwargs): # real signature unknown
 """ Size of object in memory, in bytes. """
 pass

 # 设置print(obj)打印的信息，默认是对象的内存地址等信息
 def __str__(self, *args, **kwargs): # real signature unknown
 """ Return str(self). """
 pass

 @classmethod # known case
 def __subclasshook__(cls, subclass): # known special case of object.__subclasshook__
 """
 Abstract classes can override this to customize issubclass().

 This is invoked early on by abc.ABCMeta.__subclasscheck__().
 It should return True, False or NotImplemented. If it returns
 NotImplemented, the normal algorithm is used. Otherwise, it
 overrides the normal algorithm (and the outcome is cached).
 """
 pass
 # 某个对象是由什么类创建的，如果是object，则是type类<class 'type'>
 __class__ = None
 # 将对象中所有的属性放入一个字典，例如{'name':'Leo','age':32}
 __dict__ = {}
 # 类的doc信息
 __doc__ = ''
 # 类属于的模块,如果是在当前运行模块，则是__main__，如果是被导入，则是模块名（即py文件名去掉.py）
 __module__ = ''

class Foo(object):
 def __init__(self):
 self.name = 'Alex'

 def __getattribute__(self, item):
 print("__getattribute__ in Foo")
 return object.__getattribute__(self, item)


if __name__ == '__main__':
 f = Foo()
 print(f.name) # name属性存在 或者 getattr(f,name)
 print(f.age) # age属性不存在

class Foo(object):
 def __init__(self):
 self.name = 'Alex'

 def __getattribute__(self, item):
 print("__getattribute__ in Foo")
 return object.__getattribute__(self, item)

 def __getattr__(self, item):
 print("%s不存在,但我可以返回一个值" % item)
 return 54


if __name__ == '__main__':
 f = Foo()
 print(f.name) # name属性存在
 print(f.age) # age属性不存在,但__getattr__方法返回了54，所以这里打印54。

__getattribute__ in Foo
Alex
__getattribute__ in Foo
age不存在,但我可以返回一个值
54

class Foo(object):
 def __init__(self):
  self.name = 'Alex'

 # obj.xxx = value时调用
 def __setattr__(self, key, value):
  print('setattr')
  return object.__setattr__(self, key, value)


if __name__ == '__main__':
 f = Foo()
 f.name = 'Jone' # 打印setattr
 print(f.name)

class Foo(object):
 def __init__(self):
  self.name = 'Alex' # 这里也要调用__setattr__
　　...

class Local(object):
 def __init__(self):
  # 这里不能直接使用self.DIC={}，因为__setattr__被重写了
  object.__setattr__(self, 'DIC', {})

 def __setattr__(self, key, value):
  self.DIC[key] = value

 def __getattr__(self, item):
  return self.DIC.get(item, None)


if __name__ == '__main__':
 obj = Local()
 obj.name = 'Alex' # 向DIC字典中存入值
 print(obj.name) # 从DIC字典中取出值

if hasattr(f,'xxx'): # 判断f对象中是否存在属性xxx
 delattr(f, 'xxx') # 如果存在则删除。当xxx不存在时删除会报错
 # del f.xxx # 同上

f = Foo()
print(f.__dir__()) # ['name', '__module__', '__init__', '__setattr__', '__getattribute__', '__dir__', '__dict__', '__weakref__', '__doc__', '__repr__', '__hash__', '__str__', '__delattr__', '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__', '__new__', '__reduce_ex__', '__reduce__', '__subclasshook__', '__init_subclass__', '__format__', '__sizeof__', '__class__']

f1 = Foo()
f2 = f1
print(f1 == f2) # True
print(f1 is f2) # True
print(hash(f1) == hash(f2)) # True

class Foo(object):
 def __init__(self):
  self.name = 'Alex' # 这里也要调用__
  self.ccc = object.__class__
 def __eq__(self, other):
  return self.name==other.name

f1 = Foo()
f2 = Foo()
print(f1 == f2) # True
print(f1 is f2) # False
print(hash(f1) == hash(f2)) # 抛出异常TypeError错误

class Foo(object):
 def __init__(self):
  self.name = 'Alex'

 def __str__(self):
  return "我是Foo"


if __name__ == '__main__':
 f1 = Foo()
 print(f1) # 打印 我是Foo

>>> class Foo(object):
...  def __str__(self):
...    return "我是Foo"
...
>>> f1 = Foo()
>>> print(f1)
我是Foo
>>> f1
<__main__.Foo object at 0x0000023BF701C550>

class Foo(object):
 def __init__(self):
  self.name = 'Alex'

 def __repr__(self):
  return "我是Foo"


if __name__ == '__main__':
 f1 = Foo()
 print(f1) # 打印 我是Foo

>>> class Foo(object):
...  def __repr__(self):
...    return "我是Foo"
...
>>> f1 = Foo()
>>> print(f1)
我是Foo
>>> f1
我是Foo

>>> class Foo():
...  def __str__(self):
...    return "我是Foo---str"
...  def __repr__(self):
...    return "我是Foo---repr"
...
>>> f1 = Foo()
>>> print(f1)
我是Foo---str
>>> f1
我是Foo---repr

print(f1.__class__) # <class '__main__.Foo'>

print(f1.__dict__) # {'name': 'Alex'} 只有一个属性name

class Foo(object):
 def __init__(self):
  self.name = 'Alex'


if __name__ == '__main__':
 f1 = Foo()
 print(f1.__module__) # 打印__main__

import test3

f = test3.Foo()
print(f.__module__) # 打印test3

class Foo(object):
 """
 这是一个类，名叫Foo
 """
 def __init__(self):
  self.name = 'Alex'


if __name__ == '__main__':
 f1 = Foo()
 print(f1.__doc__) # 打印 这是一个类，名叫Foo