Nick Craig-Wood wrote: > Lad <[EMAIL PROTECTED]> 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.
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