code: def _parameterize_string(raw):
      
  
      parts = []
      s_index = 0
  
      for match in _PARAMETER_PATTERN.finditer(raw):
          parts.append(raw[s_index:match.start()])
          parts.append({u"Ref": match.group(1)})
          s_index = match.end()
  
      if not parts:
          return GenericHelperFn(raw)
  
      parts.append(raw[s_index:])
      return GenericHelperFn({u"Fn::Join": [u"", parts]})
docs: Substitute placeholders in a string using CloudFormation references
  
      Args:
          raw (`str`): String to be processed. Byte strings are not
          supported; decode them before passing them to this function.
  
      Returns:
          `str` | :class:`troposphere.GenericHelperFn`: An expression with
              placeholders from the input replaced, suitable to be passed to
              Troposphere to be included in CloudFormation template. This will
              be the input string without modification if no substitutions are
              found, and a composition of CloudFormation calls otherwise.