Python进阶(三十二)-local variable 'xxx' referenced before assignment
2017-04-06 16:38
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Python进阶(三十二)-local variable ‘xxx’ referenced before assignment
这个问题很囧,在外面定义了一个变量 xxx ,然后在Python的一个函数里面引用这个变量,并改变它的值,结果报错local variable ‘xxx’ referenced before assignment,代码如下:xxx = 23 def PrintFileName(strFileName): if xxx == 23: print strFileName xxx = 24 PrintFileName("file")
错误的意思就是xxx这个变量在引用前还没有定义,这上面不是定义了么?但是后来我把xxx = 24这句去掉之后,又没问题了,后来想起python中有个global关键字是用来引用全局变量的,尝试了一下,果然可以了:
xxx = 23 def PrintFileName(strFileName): global xxx if xxx == 23: print strFileName xxx = 24 PrintFileName("file")
原来在python的函数中和全局同名的变量,如果你有修改变量的值就会变成局部变量,在修改之前对该变量的引用自然就会出现没定义这样的错误了,如果确定要引用全局变量,并且要对它修改,必须加上global关键字。
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