How to replace the last (and only last) character in a string?

[Johny]

On May 3, 4:37 pm, kyoso... at gmail.com wrote:
> On May 3, 9:27 am, Johny <pyt... at hope.cz> wrote:
>
> > Let's suppose
> > s='12345 4343 454'
> > How can I replace the last '4' character?
> > I tried
> > string.replace(s,s[len(s)-1],'r')
> > where 'r' should replace  the last '4'.
> > But it doesn't work.
> > Can anyone explain why?
>
> > Thanks
> > L.
>
> I think the reason it's not working is because you're doing it kind of
> backwards. For one thing, the "string" module is deprecated. I would
> do it like this:
>
> s = s.replace(s[len(s)-1], 'r')
>
> Although that is kind of hard to read. But it works.
>
> Mike


Mike it does NOT work for me.
>>> s.replace(s[len(s)-1], 'r')
'123r5 r3r3 r5r'

I need only the last character to be replaced