[Tutor] bug in exam score conversion program

[Steve Willoughby]

Dragos Ionescu wrote:
> ---- Original Message ----
> From: Steve Willoughby <steve at alchemy.com>
> To: Dragos Ionescu <idragos at ymail.com>
> Cc: bob gailer <bgailer at gmail.com>; David <ldl08 at gmx.net>; tutor at python.org
> Sent: Saturday, October 4, 2008 11:04:30 PM
> Subject: Re: [Tutor] bug in exam score conversion program
> 
> Dragos Ionescu wrote:
>  > ----- Original Message ----
>  > From: bob gailer <bgailer at gmail.com <mailto:bgailer at gmail.com>>
>  > To: David <ldl08 at gmx.net <mailto:ldl08 at gmx.net>>
>  > Cc: tutor at python.org <mailto:tutor at python.org>
>  > Sent: Saturday, October 4, 2008 10:15:10 PM
>  > Subject: Re: [Tutor] bug in exam score conversion program
>  >
>  > Lots of good responses. And now for something completely different:
>  >
>  > import string
>  > x = string.maketrans('567891', 'FDCBAA')
>  > score = raw_input('score>')
>  > print "Your grade is:", score[0].translate(x)
>  > --
>  > Bob Gailer
>  > Chapel Hill NC
>  > 919-636-4239
>  >
>  > When we take the time to be aware of our feelings and
>  > needs we have more satisfying interatctions with others.
>  >
>  > Nonviolent Communication provides tools for this awareness.
>  >
>  > As a coach and trainer I can assist you in learning this process.
>  >
>  > What is YOUR biggest relationship challenge?
>  >
>  > _______________________________________________
>  > Tutor maillist  -  Tutor at python.org <mailto:Tutor at python.org> 
> <mailto:Tutor at python.org <mailto:Tutor at python.org>>
>  > http://mail.python.org/mailman/listinfo/tutor
>  > 
>  > 
>  > Wow! Bob Gailer's solution is so elegant. Can someone plese explain what
>  > is the algorithm behind  string.maketrans. More exactly, how is this
>  > function doing the coding?
> 
> Actually, I don't think the point was to be elegant as much
> as to get you thinking about something you might not have
> explored--never hurts to keep learning new features so you
> don't inefficiently apply the same old small set of things
> to new problems.
> 
> You wouldn't *really* want to implement a production grade
> system like that, cute though it is.  This is setting up a
> translation table mapping the first character in the score
> to a letter grade.  So a 9 is changed to an A.  The obvious
> problem though is how it handles a score of, say, "1".  Or,
> for that matter, "37".
> 
> 
> I know how string.maketrans works. I was wondering how to implement such 
> a function. Would that be very hard? I must admit that I was 'surprised' 
> when I printed x...

How to implement... the equivalent of maketrans/translate?  Pretty
easy really.  maketrans just builds a 256-byte table showing a mapping
from one character set to another (compare perl's y/// or tr///).  Once 
you have that translation table, all you really need to do is take each 
character of a string and make a new string by looking up each source 
character and returning what the table says (effectively table[ord(i)] 
for each character i in the source string).  Which is pretty much
what string.translate() is doing.

or did I misunderstand which function you wanted to implement?