[Tutor] why does this fail

[Christian Witts]

On 25/08/2010 12:00, Roelof Wobben wrote:
> Hello,
>
> I have this programm :
>
> def remove_letter(letter, strng):
>     """
> >>> remove_letter('a', 'apple')
>       'pple'
> >>> remove_letter('a', 'banana')
>       'bnn'
> >>> remove_letter('z', 'banana')
>       'banana'
> >>> remove_letter('i', 'Mississippi')
>       'Msssspp'
>     """
>     antwoord=""
>     for letter in strng:
>         print letter, strng
>         if letter in strng:
>             print "false"
>         else:
>             print "true"
>     return antwoord
>
> x=remove_letter('a', 'apple')
> print x
>
> But now everything is false even a in apple.
>
> What is here wrong ?
>
> Roelof
>
>
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>    

You're rebinding the variable `letter`.
It is an input variable for your function but then you use it as the 
character store while iterating through your string variable `strng`.

What your control should look like would be more like

for character in strng:
     if letter == character:
         print 'false' # this should be true, it is a match just like in 
your example
     else:
         print 'true'

I'm assuming this function is just for learning purposes because there's 
a built-in string function you can use called replace and you'd use it 
as such `'apple'.replace('a', '')`.

PS: Once you've gotten it to work convert it to a list comprehension, 
they are incredibly useful and a great tool.

-- 
Kind Regards,
Christian Witts