Local variable 'xxx' referenced before assignment

This problem is very difficult. A variable XXX is defined outside, and then this variable is referenced in a function in Python and its value is changed, the error "local variable 'xxx' referenced before assignment" is returned,CodeAs follows:

Xxx = 23 <br/> def printfilename (strfilename): <br/> If xxx = 23: <br/> Print strfilename <br/> xxx = 24 </P> <p> printfilename ("file ")

The error means that the variable XXX has not been defined before reference. Isn't it defined above? However, after I removed xxx = 24, it was okay. Later I remembered that there was a global keyword in Python that was used to reference global variables. I tried it and it was okay:

Xxx = 23 <br/> def printfilename (strfilename): <br/> global XXX <br/> If xxx = 23: <br/> Print strfilename <br/> xxx = 24 </P> <p> printfilename ("file ")

In Python functions, if you change the value of a variable to a local variable, before modification, the reference to this variable will naturally lead to the failure to define such an error. If you are sure to reference the global variable and want to modify it, you must add the Global keyword.

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