[Tutor] FW: find() problem

[Roelof Wobben]

Hello, 

 

I found it.

This one does the trick :

 

def find(strng, ch, start, step=1):
    index=start
    while 0 <= index < len(strng):
        if strng[index] == ch:
              return index 
        index += step
    return -2


fruit=""
letter=""
fruit= raw_input("Enter a sort of fruit: ")
letter = raw_input("Enter the character which must be counted: ")
index=1
aantal=0
while 0 <=index < len(fruit):
    x=find (fruit,letter, index)
    index=x+1
    if x<>-2 :
        aantal=aantal+1
print "De letter", letter , "komt", aantal , "maal voor in het woord", fruit

 

Roelof


 
> Subject: Re: [Tutor] FW: find() problem
> From: evert.rol at gmail.com
> Date: Tue, 24 Aug 2010 17:44:22 +0200
> CC: tutor at python.org
> To: rwobben at hotmail.com
> 
> > > > > > def find(strng, ch, start, step=1):
> > > > > > index = start
> > > > > The problem lies here, if you do a print on index, it never gets past
> > > > > the first index of the number, so
> > > > > your while loop below goes into an infinite loop.
> > > > > 
> > > > > For example:
> > > > > find('starfruit','t',0) <- First time will return 1
> > > > > find('starfruit','t',1) <- Still returns 1. Infinite loop
> > > > > 
> > > > > > while 0 <= index < len(strng):
> > > > > > if strng[index] == ch:
> > > > > > return index
> > > > > > index += step
> > > > > > return -1
> 
> Why are you returning -1 here? 
> -1 is a valid list index. 
> And with your last change, it makes your main condition valid.
> 
> 
> > > > > >
> > > > > > fruit=""
> > > > > > letter=""
> > > > > > fruit= raw_input("Enter a sort of fruit: ")
> > > > > > letter = raw_input("Enter the character which must be counted: ")
> > > > > > start=0
> > > > > > aantal=0
> > > > > > while 0 <=start < len(fruit):
> > > > > > x=find (fruit,letter, start)
> > > > > > aantal +=1
> > > > > > start=x
> > > > > > print "De letter", letter , "komt", aantal , "maal voor in het woord", fruit
> > > > > >
> > > > > 
> > > > > HTH,
> > > > > Tino
> > > > 
> > > > Hello, 
> > > > 
> > > > Your right. index get never past 1 
> > > > But in my opinion when something is found then x will be the place where the character is be found.
> > > > After that the counter is increased and start gets the value of x.
> > > > So start should change.
> > > > 
> > > > Now finding out why this is not happening.
> > > 
> > > You're including the previous found index; so it will just find the character at that same index again. You need to start the next search one index further down the word.
> > 
> > 
> > Hello Evert.
> > 
> > Stupid mistake.
> > I change start=x to start=x+1 
> > But still it's not working properly.
> > 
> > I can see that on this example.
> > 
> > Fruit : banaan
> > letter : a
> > 
> > That a is being found at 2,4,5 which is correct but the programm don't end.
> > So there's another error somewhere,
> > 
> > Roelof
> > 
> > > 
> > > 
> > > > 
> > > > But thanks for the help.
> > > > 
> > > > Roelof
> > > > 
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