关于pyhton中的__xxx__格式的方法与变量的理解

python中类似__xx__的方法和变量是python系统内定义的方法和变量，都是具有特殊意义的基础变量和方法，一般不要擅自使用，除非知道自己在干什么。

具体查看python内置模块builtins.py，里面定义了内置方法、对象和异常，这些定义是最基本的定义。

一、__xx__格式的方法：

一般定义在object类中，object类是大多数python类的基类，这些__xx__格式的方法代表了内置方法，是允许一个类的重要属性。很多方法会被自动调用：

如类初始化时调用__init__()方法，str(obj)调用__str__()方法

内置函数与__xx__格式函数对应表：

dir  __dir__

str __str__

dict __dict__

等等

class object:
    """ The most base type """
    def __delattr__(self, *args, **kwargs): # real signature unknown
        """ Implement delattr(self, name). """
        pass

    def __dir__(self): # real signature unknown; restored from __doc__
        """
        __dir__() -> list
        default dir() implementation
        """
        return []

    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def __format__(self, *args, **kwargs): # real signature unknown
        """ default object formatter """
        pass

    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    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

    def __init__(self): # known special case of object.__init__
        """ Initialize self.  See help(type(self)) for accurate signature. """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    @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

    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

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __setattr__(self, *args, **kwargs): # real signature unknown
        """ Implement setattr(self, name, value). """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """
        __sizeof__() -> int
        size of object in memory, in bytes
        """
        return 0

    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

    __class__ = None # (!) forward: type, real value is ''    __dict__ = {}    __doc__ = ''    __module__ = ''

二、__xx__格式的变量：