human
Solve the following python programming problem given the following code:
def focus_index(self) : 
    def _f(widget) : 
        if isinstance (widget, Viewers.GingaViewerWidget) : 
            widget.focus () 
            return True 
if isinstance (widget, Widgets.ContainerBase) : 
            for child in widget.get_children () : 
                if _f (child) : 
                    return True 
return False 
return False 
cur_idx = self.nb.get_index () 
    child = self.nb.index_to_widget (_f) 
    _f (child) 

    
    

    Fix the buggy line: child = self.nb.index_to_widget (_f)
assistant
#Here is Python program to fix the buggy line: child = self.

child = self.nb.index_to_widget (cur_idx)