code: def ahead(self, i, j=None):
          '''Raising stopiteration with end the parse.
          '''
          if j is None:
              return self._stream[self.i + i]
          else:
              return self._stream[self.i + i: self.i + jf ahead(self, i, j=None):
          '''Raising stopiteration with end the parse.
          '''
          if j is None:
              return self._stream[self.i + i]
          else:
              return self._stream[self.i + i: self.i + j]
docs: Raising stopiteration with end the parse.