Problem with regex

[Emekadavid]

I want to take:

s = '1 w 2 r 3g'

And format it to:

s = '1 W 2 R 3g'

Based on the concept that the first letter after any space is converted to upper including the first letter.
I tried:

s.title()

but did not get good results. I then tried regex.

pattern = '\s\w|^\w'
re.finditer(pattern, s)

Which found all the matches but I have a problem. Now that is found the matches, how do I convert the matched letters to uppercase? Can someone help me. I tried using indexing but the interpreter gave error that no item assignment is allowed with strings. Immutable. Can someone suggest how I can solve this now that am halfway through?

[Gribouillis]

This should work

re.sub(r'(?:(?<=\s)|^)\w', lambda m: m.group(0).upper(), s)