docs: def regexp_prompt(prompt, regexp='.', answer=''):
      '''Ask the user for a text entry that matches a regular expression
  
         Parameters
         ==========
         prompt: the prompt to ask the user
         regexp: the regular expression to match. defaults to anything.
      
      '''
      get_input = getattr(__builtins__, 'raw_input', input)
      while not re.search(regexp, answer):
          answer = get_input(prompt + ': ').strip()
          # If the option isn't valid, this is shown next
          message = "Your entry must match the regular expression %s" %regexp    
  
      return answer