While and raw_input

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While and raw_input

 
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  #1
Sep 12th, 2009
Can someone please tell me what I am doing wrong. I know this is easy, but I haven't managed to make it work properly.
python Syntax (Toggle Plain Text) 
  1. overwrite = None
  2. while overwrite != 'Y'.lower() or overwrite != 'N'.lower():
  3.     overwrite = raw_input("Do you want to overwrite (Y/N)? ")

It doesn't exit the while loop.

Thanks.
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Re: While and raw_input

 
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  #2
Sep 12th, 2009
You are creating a situation where the while loop exit condition is always True. Test this ...
python Syntax (Toggle Plain Text) 
  1. overwrite = None
  2. while overwrite != 'y' or overwrite != 'n':
  3.     overwrite = raw_input("Do you want to overwrite (Y/N)? ").lower()
  4.     print overwrite != 'y'
  5.     print overwrite != 'n'
  6.     # overall condition
  7.     print False or True
Easier to understand is this approach ...
python Syntax (Toggle Plain Text) 
  1. while True:
  2.     overwrite = raw_input("Do you want to overwrite (Y/N)? ").lower()
  3.     if overwrite == 'y' or overwrite == 'n':
  4.         break
... or even simpler ...
python Syntax (Toggle Plain Text) 
  1. while True:
  2.     overwrite = raw_input("Do you want to overwrite (Y/N)? ").lower()
  3.     if overwrite in 'yn':
  4.         break
Last edited by vegaseat; Sep 12th, 2009 at 3:49 pm.
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Re: While and raw_input

 
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  #3
Sep 12th, 2009
For future coding conundrums, an "or" can be viewed as an if / elif, and "and" can be viewed as two nested if statements, which you would adapt to while() statements.
Python Syntax (Toggle Plain Text) 
  1. while overwrite != 'Y'.lower() or overwrite != 'N'.lower():  becomes
  2. if overwrite != 'Y'.lower():
  3.     do something
  4. elif overwrite != 'N'.lower():
  5.     do the same thing
  6.  
  7. For completeness, the 'and' would be
  8. if overwrite != 'Y'.lower() and overwrite != 'N'.lower():  becomes
  9. if overwrite != 'Y'.lower():
  10.     if overwrite != 'N'.lower():
  11.        do something
Hopefully this will help sort out the and/or's in the future.
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Re: While and raw_input

 
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  #4
Sep 13th, 2009
What woooee said was correct:
python Syntax (Toggle Plain Text) 
  1. overwrite=""
  2. while(overwrite!="Y".lower() and overwrite!="N".lower()):
  3.     overwrite=raw_input()
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Re: While and raw_input

 
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  #5
Sep 13th, 2009
Thanks vegaseat, woooee and sravan953. You were all very helpful.
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Re: While and raw_input

 
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Sep 13th, 2009
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Originally Posted by sravan953 View Post
What woooee said was correct:
python Syntax (Toggle Plain Text) 
  1. overwrite=""
  2. while(overwrite!="Y".lower() and overwrite!="N".lower()):
  3.     overwrite=raw_input()
Here "Y".lower() does not make any sense since it is simply 'y'
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Re: While and raw_input

 
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  #7
Sep 13th, 2009
@sneekula, that is what nunos wanted.
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