How to use the pynvim.autocmd function in pynvim

    @neovim.autocmd('VimEnter', pattern='*', sync=True)
    def event_vim_enter(self):
        """Find and retain the plugin instance."""
        # Don't import semshi on top so it's not collected as a plugin again
        from semshi.plugin import Plugin
        # Using the garbage collector interface to find the instance is a bit
        # hacky, but works reasonably well and doesn't require changes to the
        # plugin code itself.
        for obj in gc.get_objects():
            if isinstance(obj, Plugin):
                self._plugin = obj
                return
        raise Exception('Can\'t find plugin instance.')

    @pynvim.autocmd('BufEnter', pattern='*', eval='expand("")')
    def onBufEnter(self, path):
        if not self._hasInitialized:
            return
        try:
            self._onBufEnterInternal(path)
        except Exception as e:
            self._log.exception(e)

    @neovim.autocmd('VimLeave', sync=True)
    def event_vim_leave(self):
        for handler in self._handlers.values():
            handler.shutdown()