code: def parse_partial(self, stream):
          
          result = self(stream, 0)
  
          if result.status:
              return (result.value, stream[result.index:])
          else:
              raise ParseError(result.expected, stream, result.furthest)
docs: Parse the longest possible prefix of a given string.
          Return a tuple of the result and the rest of the string,
          or raise a ParseError.