Trouble with regular expressions

MRAB google at mrabarnett.plus.com
Sat Feb 7 15:37:31 CET 2009


LaundroMat wrote:
> Hi,
> 
> I'm quite new to regular expressions, and I wonder if anyone here
> could help me out.
> 
> I'm looking to split strings that ideally look like this: "Update: New
> item (Household)" into a group.
> This expression works ok: '^(Update:)?(.*)(\(.*\))$' - it returns
> ("Update", "New item", "(Household)")
> 
> Some strings will look like this however: "Update: New item (item)
> (Household)". The expression above still does its job, as it returns
> ("Update", "New item (item)", "(Household)").
> 
> It does not work however when there is no text in parentheses (eg
> "Update: new item"). How can I get the expression to return a tuple
> such as ("Update:", "new item", None)?
> 
You need to make the last group optional and also make the middle group 
lazy: r'^(Update:)?(.*?)(?:(\(.*\)))?$'.

(?:...) is the non-capturing version of (...).

If you don't make the middle group lazy then it'll capture the rest of 
the string and the last group would never match anything!



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