<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def go_to_previous_tab(self):
 """ Focus the previous tab. """

        self.active_tab_index = (self.active_tab_index - 1 +
                                 len(self.tab_pages)) % len(self.tab_pages)