No doubt I should know this regex point but ..

[Jim Hefferon]

I am writing a class that walks through a file tree and (among other things)
filters out which files it considers.  So I want to have 
  __init__( .. ,filterExpression='..')
For the default I want to filter nothing.  So I need a Python regular expression
that never matches.  What is (the best) one?

Thanks for any help, 
Jim