regex (?!..) problem

[Hans Mulder]

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