Python 变量范围和类 [英] Python Variable Scope and Classes

问题描述

在 Python 中，如果我定义一个变量:

In Python, if I define a variable:

my_var = (1,2,3)

并尝试在类的__init__函数中访问它:

and try to access it in __init__ function of a class:

class MyClass:
    def __init__(self):
        print my_var

我可以访问它并打印 my_var 而不声明(全局 my_var).

I can access it and print my_var without stating (global my_var).

如果我把 my_var 放在 class MyClass 之后，我会得到范围错误 (no global variable found).

If I put my_var right after class MyClass however, I get scope error (no global variable found).

这是什么原因?我该怎么做?我在哪里可以阅读有关此内容的信息?我确实阅读了 Python Class 页面，但没有遇到它的解释.

What is the reason for this? How should I do this? Where can I read about this to learn? I did read Python Class page but I did not encounter its explanation.

谢谢

推荐答案

当你把它放在 class MyClass 之后，它就变成了一个类属性，你可以通过 MyClass 访问它.my_var 或类中的 self.my_var(前提是您没有创建同名的 instance 变量).

When you put it right after class MyClass, it becomes a class attribute and you can get access to it via MyClass.my_var or as self.my_var from within the class (provided you don't create an instance variable with the same name).

这是一个小演示:

my_var = 'global'
class MyClass(object):
   my_var = 'class' 
   def __init__(self):
      print my_var #global
      print MyClass.my_var #class
      print self.my_var #class -- Only since we haven't set this attribute on the instance
      self.my_var = 'instance' #set instance attribute.
      print self.my_var #instance
      print MyClass.my_var #class

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