code: def filter_whitespace(mode: str, text: str) -> str:
      
      if mode == "all":
          return text
      elif mode == "single":
          text = re.sub(r"([\t ]+)", " ", text)
          text = re.sub(r"(\s*\n\s*)", "\n", text)
          return text
      elif mode == "oneline":
          return re.sub(r"(\s+)", " ", text)
      else:
          raise Exception("invalid whitespace mode %s" % mode)
docs: Transform whitespace in ``text`` according to ``mode``.
  
      Available modes are:
  
      * ``all``: Return all whitespace unmodified.
      * ``single``: Collapse consecutive whitespace with a single whitespace
        character, preserving newlines.
      * ``oneline``: Collapse all runs of whitespace into a single space
        character, removing all newlines in the process.
  
      .. versionadded:: 4.3