<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_deep_focus(self, startfrom=None):
 """return the bottom most focussed widget of the widget tree"""

        if not startfrom:
            startfrom = self.current_buffer
        if 'get_focus' in dir(startfrom):
            focus = startfrom.get_focus()
            if isinstance(focus, tuple):
                focus = focus[0]
            if isinstance(focus, urwid.Widget):
                return self.get_deep_focus(startfrom=focus)
        return startfrom