python local variable 'xxx' referenced before assignment

# -*- coding:utf-8 -*-
 2  import sys
 3 
 4  def ms_fun():
 5     obj = 3
 6     def ms_k():
 7         if  obj is not 4:
 8             obj = 4
 9             print(obj)
10     ms_k()
11 
12  if __name__ == '__main__':
13     ms_fun()

上述代码会抛出 UnboundLocalError:local variable 'obj' referenced before assignment 的异常

# -*- coding:utf-8 -*-
import sys

def ms_fun():
    obj = 3
    def ms_k():
        #global obj
        if  obj is not 4:
            global obj
            obj = 4
            print(obj)
    ms_k()

if __name__ == '__main__':
    ms_fun()

上述代码会抛出NameError: global name 'obj' is not defined

总结一下:如果你和我一样,熟悉javascript的语法,并且刚开始接触python.那么你很容易受javascript的语法 ,陷入习惯性思维误区.python的语法更灵活多变,甚至有些诡异.

如果内部函数有引用外部函数的同名变量,并且对这个变量有修改.那么python会认为它是一个局部变量.可以这样改

# -*- coding:utf-8 -*-
import sys

obj = 3
def ms_fun():
    def ms_k():
        global obj
        if obj is not 4:
            obj = 4
            print(obj)
    ms_k()

if __name__ == '__main__':
    ms_fun()