regex (?!..) problem

Hans Mulder hansmu at
Tue Oct 6 21:12:39 CEST 2009

Stefan Behnel wrote:
> Wolfgang Rohdewald wrote:
>> I want to match a string only if a word (C1 in this example) appears
>> at most once in it.
>     def match(s):
>         if s.count("C1") > 1:
>             return None
>         return s
> If this doesn't fit your requirements, you may want to provide some more
> details.

That will return a false value if s is the empty string.

How about:

     def match(s):
         return s.count("C1") <= 1

-- HansM

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