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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 _send_string_selection(self, string: str):
 """Use the mouse selection clipboard to send a string."""

        backup = self.clipboard.selection  # Keep a backup of current content, to restore the original afterwards.
        if backup is None:
            logger.warning("Tried to backup the X PRIMARY selection content, but got None instead of a string.")
        self.clipboard.selection = string
        self.__enqueue(self._paste_using_mouse_button_2)
        self.__enqueue(self._restore_clipboard_selection, backup)