def previous(self, cli):
        """
        Return the previously focussed :class:`.Buffer` or `None`.
        """
        if len(self.focus_stack) > 1:
            try:
                return self[self.focus_stack[-2]]
            except __HOLE__:
                pass
dataset/ETHPy150Open jonathanslenders/python-prompt-toolkit/prompt_toolkit/buffer_mapping.py/BufferMapping.previous