<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def timeline(self):
 """Get timeline, reloading the site if needed."""

        rev = int(self.db.get('site:rev'))
        if rev != self.revision:
            self.reload_site()

        return self._timeline