<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def previous_row(self):
 """Select previous row in list widget."""

        if self.mode == self.SYMBOL_MODE:
            self.select_row(-1)
            return
        prev_row = self.current_row() - 1
        if prev_row >= 0:
            title = self.list.item(prev_row).text()
        else:
            title = ''
        if prev_row == 0 and '</b></big><br>' in title:
            self.list.scrollToTop()
        elif '</b></big><br>' in title:
            # Select the next previous row, the one following is a title
            self.select_row(-2)
        else:
            self.select_row(-1)