python魔法方法之-Python __repr__()方法：显示属性

教程参考学习:http://c.biancheng.net/view/2367.html

repr()

默认情况下，repr() 会返回和调用者有关的 “类名+object at+内存地址”信息。当然，我们还可以通过在类中重写这个方法，从而实现当输出实例化对象时，输出我们想要的信息。

举个例子：

class CLanguage:
    def __init__(self):
        self.name = "C语言中文网"
        self.add = "http://c.biancheng.net"
    def __repr__(self):
        return "CLanguage[name="+ self.name +",add=" + self.add +"]"
clangs = CLanguage()
print(clangs)

程序运行结果为：
CLanguage[name=C语言中文网,add=http://c.biancheng.net]

由此可见，repr() 方法是类的实例化对象用来做“自我介绍”的方法，默认情况下，它会返回当前对象的“类名+object at+内存地址”，而如果对该方法进行重写，可以为其制作自定义的自我描述信息。

object是所有类的基类

儿子继承父亲，同时儿子也可以优化父亲留下来的东西

Python中一切皆为对象，类也不例外，类也是一个对象。
object是所有类的基类。
基类几乎什么行为都不包括，我们可以创建一个实例，但是很多事情无法完成，因为很多特殊方法的程序会跑出异常

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

    def __dir__(self, *args, **kwargs): # real signature unknown
        """ Default dir() implementation. """
        pass

    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, *args, **kwargs): # real signature unknown
        """ Size of object in memory, in bytes. """
        pass

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

实例化

下面来看一个初学者经常出错的问题：

从这里可以看出类中的“self是类实例化产生的对象本身的指代，而不能指代此类本身”

class Study:
    def get_knowledge(self):
        return self.learn_time * self.learn_efficiency

s = Study
s.learn_time, s.learn_efficiency = 3, 2
print(s.get_knowledge()) #output :TypeError: get_knowledge() missing 1 required positional argument: 'self'