[Tutor] position

[linda.s]

On 10/27/07, Alan Gauld <alan.gauld at btinternet.com> wrote:
>
> "linda.s" <samrobertsmith at gmail.com> wrote
>
> >I have a string a= "qq,eee,rrr".
> >>>> a.index(",")
> > 2
> > It is the position of the first "," in a.
> > Is that possible to find the Nth "," in a if a is a very long string
> > and I need know the position of the Nth ","?
>
> Yes but not directly.
> index takes a couple of optional parameters
>
>     S.index(sub [,start [,end]]) -> int
>
> So by repeating the index call in a loop using the previous
> index as youur start position you an get it
>
> untested pseudo code
>
> def nth_index(aString, aChar, N):
>     n = 0
>     for i in range(N):
>         n = aString.index(aChar, n)
>     return n
>
should be:
def nth_index(aString, aChar, N):
   n = 0
   for i in range(N):
       n = aString.index(aChar, n+1)
   return n