code: def _unquote(data):
      
      if not data.startswith(b'"') or not data.endswith(b'"'):
          return data
      return QUOTE_RE.sub(b"\\1", data[1:-1])
docs: Unquote quoted value from DIGEST-MD5 challenge or response.
  
      If `data` doesn't start or doesn't end with '"' then return it unchanged,
      remove the quotes and escape backslashes otherwise.
  
      :Parameters:
          - `data`: a quoted string.
      :Types:
          - `data`: `bytes`
  
      :return: the unquoted string.
      :returntype: `bytes`