python - 为什么类方法访问它的类变量中需要 `global var`？

Question

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()

Answer 1

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