Question

问题陈述：如何在Java中使用类似' this'的同一类更新全局变量？

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！

注释： 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？救命。

Answer 1

你可能会尝试做不同的事情，你可能需要research a little bit more关于python本身，但是让我们看看这是否有帮助：

如果你想让一个实例共享一个共同响应的类，你可以这样：

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!"

另一方面，如果您希望每个实例都有自己的响应（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，如果你真的想要一个global variable（not really advised改变类实例之外的任何内容，你应该将它作为参数传递给改变它的方法）：

# 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!"

如何从同一个类中更新全局变量？蟒蛇

1 个答案: