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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def focusNextPrevChild(self, next_child):
 """ The default 'focusNextPrevChild' implementation. """

        fd = focus_registry.focused_declaration()
        if next_child:
            child = self.declaration.next_focus_child(fd)
            reason = Qt.TabFocusReason
        else:
            child = self.declaration.previous_focus_child(fd)
            reason = Qt.BacktabFocusReason
        if child is not None and child.proxy_is_active:
            return child.proxy.tab_focus_request(reason)
        widget = self.widget
        return type(widget).focusNextPrevChild(widget, next_child)