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 Craig-Wood <[EMAIL PROTECTED]> -- http://www.craig-wood.com/nick
--
http://mail.python.org/mailman/listinfo/python-list
