如何更新同一个类中的全局变量？ Python

Question

问题描述：如何在同一个类中更新全局变量，如'this' in Java？

代码示例：

class XYZ(object): 

    response = "Hi Pranjal!"; 

    def talk(response): 
     self.response = response;   #Class attribute should be assiged Anand value! 

    talk("Hi Anand!"); 
    print response; 

输出应该是： 嗨阿南德！

评论： 错误！ '自我'没有定义！

如何通过在同一个类中调用该函数（talk）来更新全局变量（响应）。我理解使用self，我需要传递一个对象，但是我不能在同一个类中创建一个类的实例吗？帮帮我。

Answer 1

还有，你可以尝试做不同的事情，你可能需要research a little bit more关于Python本身，而是让我们看看这可以帮助：如果你想有一个类，其实例都有一个共同的响应

，你可以有这样的事情：

class XYZ(object): 
    response = "Hi Pranjal!"; # class atribute 

    def change_talk(self, response): 
     # class methods always get `self` (the object through which they are 
     # called) as their first argument, and it's commons to call it `self`. 
     XYZ.response = response # change class atribute 

    def talk(self): 
     print XYZ.response 

XYZ_inst = XYZ() # instance of the class that will have the class methods 
XYZ_inst.talk() # instance "talks" 
#"Hi Pranjal!" 
XYZ_inst.change_talk("Hi Anand!"); 
XYZ_inst.talk() 
#"Hi Anand!" 

XYZ_inst_2 = XYZ() 
## New instance has the same response as the previous one: 
XYZ_inst_2.talk() 
#"Hi Anand!" 
## And changing its response also changes the previous: 
XYZ_inst_2.change_talk("Hi Bob!") 
XYZ_inst_2.talk() 
#"Hi Bob!" 
XYZ_inst.talk() 
#"Hi Bob!" 

在另一方面，如果你想每个实例有它自己的响应（see more about __init__）：

class XYZ2(object): 
    # you must initialise each instance of the class and give 
    # it its own response: 
    def __init__(self, response="Hi Pranjal!"): 
     self.response = response 

    def change_talk(self, response): 
     self.response = response; 

    def talk(self): 
     print self.response 

XYZ_inst = XYZ2() # object that will have the class methods 
XYZ_inst.talk() 
#"Hi Pranjal!" 
XYZ_inst.change_talk("Hi Anand!"); 
XYZ_inst.talk() 
#"Hi Anand!" 

XYZ_inst_2 = XYZ2() 
## new instance has the default response: 
XYZ_inst_2.talk() 
#"Hi Pranjal!" 
## and changing it won't change the other instance's response: 
XYZ_inst_2.change_talk("Hi Bob!") 
XYZ_inst_2.talk() 
#"Hi Bob!" 
XYZ_inst.talk() 
#"Hi Anand!" 

最后，如果你真的想有一个global variable（这是not really advised为改变无论是类的实例之外，你应该把它作为参数传递给方法变更的话）：

# global variable created outside the class: 
g_response = "Hi Pranjal!" 

class XYZ3(object): 

    def change_talk(self, response): 
     # just declare you are talking with a global variable 
     global g_response 
     g_response = response # change global variable 

    def talk(self): 
     global g_response 
     print g_response 


XYZ_inst = XYZ3() # object that will have the class methods 
XYZ_inst.talk() 
#"Hi Pranjal!" 
XYZ_inst.change_talk("Hi Anand!"); 
XYZ_inst.talk() 
#"Hi Anand!" 
print g_response 
#"Hi Anand!"