How to replace a comma

[Lad]

Nick Craig-Wood wrote:
> Lad <python at hope.cz> wrote:
> >  In a text I need to add a blank(space) after a comma but only if
> >  there was no blank(space) after the comman If there was a
> >  blank(space), no change is made.
> >
> >  I think it could be a task for regular expression but can not
> >  figure out the correct regular expression.
>
> You can do it with a zero width negative lookahead assertion, eg
>
>   >>> import re
>   >>> s="One, Two,Three,Four, File"
>   >>> re.sub(r",(?!\s)", ", ", s)
>   'One, Two, Three, Four, File'
>   >>>
>
> From the help :-
>
>   (?!...)
>       Matches if ... doesn't match next. This is a negative lookahead
>       assertion. For example, Isaac (?!Asimov) will match 'Isaac ' only if
>       it's not followed by 'Asimov'
>
> Or in a more straightforward but less efficient and accurate style -
> this matches the next character which gets added back into the string.
>
>   >>> re.sub(r",([^\s])", r", \1", s)
>   'One, Two, Three, Four, File'
>   >>>
>
> This shows a fundamental difference between the two methods
>
>   >>> t = ",,,,,"
>   >>> re.sub(r",(?!\s)", ", ", t)
>   ', , , , , '
>   >>> re.sub(r",([^\s])", r", \1", t)
>   ', ,, ,,'
>   >>>
 Nick,
Thanks a lot.It works GREAT!
La.