def scroll_down(self):
        """
        Returns the next command if any.
        """
        self._index -= 1
        if self._index < 0:
            self._index = -1
            return ''
        try:
            return self._history[self._index]
        except IndexError:
            return ''
def scroll_down ( self ) : self . _index -= 1 if self . _index < 0 : self . _index = - 1 return '' try : return self . _history [ self . _index ] except IndexError : return ''
Returns the next command if any.