如何从外部类python创建类静态变量

Question

我想从类外部创建一个静态类变量，或者想要访问从外部类声明的变量。

class test(object):
    in_class = var

class test():
global var
var = 20
j = test()
print j.in_class

这给出了

Traceback (most recent call last):
  File "class_test.py", line 1, in <module>
    class test(object):
  File "class_test.py", line 2, in test
    in_class = var
NameError: name 'var' is not defined