python之为什么类方法访问它的类变量中需要 `global var`

class Test: 
    num1 = 1 
 
# CASE 1 
# WHY GLOBAL HERE? But no global below in CASE 2 
    global num2 
    num2 = 2 
 
    def printNum2(self): 
        return num2 
 
## FAILURE WITH NON-GLOBAL num2, why? 
# should print 2, with instance 
i = Test() 
print i.printNum2() 
 
 
 
# CASE 2 
# 
#AUTOMATICALLY GLOBAL SCOPE? 
num1=1 
 
def print1(): 
    return num1 
 
 
print print1() 

请您参考如下方法:

您不需要全局来使 printNum2 正常工作。相反，使用这个:

class Test: 
  num1 = 1 
  num2 = 2 
 
  def printNum2(self): 
      return self.num2 

如果您想执行以下操作，则只需要全局:

x = Test() 
print num2 
//instead of  
print x.num2