[Tutor] Don't understand error messages.

[spir]

Le Wed, 22 Apr 2009 11:57:13 -0700,
"WM." <wferguson1 at socal.rr.com> s'exprima ainsi:

[...]
> def DisplayBoard(HANGMAPIX, MissedLetters, CorrectLetters, SecretWord):
>     print HANGMANPIX[len(MissedLetters)]
>     print
> 
>     print 'MissedLetters:',
>     for Letter in MissedLetters:
>         print Letter,
>         print
> 
>         Blanks = '_' * len(SecretWord)
> 
>         for i in range(len(SecretWord)):
>             # 116 Replace Blanks with correctly guessed letters.
>             if SecrettWord[i] in CorrectLetters:
>                 Blanks = Blanks[:i] + SecretWord[i] + Blanks[i+1:]
>                
>     for Letters in Blanks:#Show SecretWord w 1 space between letters.
>         print Letter,
>     print
[...] 

> End of program, below is the error message:
>        
> Traceback (most recent call last):
>   File "C:\Python26\SweigartHangMan.py", line 212, in <module>
>     DisplayBoard(HANGMANPIX, MissedLetters, CorrectLetters, SecretWord)
>   File "C:\Python26\SweigartHangMan.py", line 183, in DisplayBoard
>     for Letters in Blanks:#Show SecretWord w 1 space between letters.
> UnboundLocalError: local variable 'Blanks' referenced before assignment
               
Python's right ;-)
You may use the word 'Blanks' without defining it.
The reason is you definie Blanks inside a "for Letter in MissedLetters" loop. If ever MissedLetters happens to be empty, the loop will never be entered and Blanks remains unknown.
Happy you! This in fact reveals a conceptual error in your program's design (BLanks should be first defined outside the loop)... that may have caused damage in a real-world case if ever not detected early enough.

Denis
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