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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 _close_connection(self):
 """Close the connection to the easyfire unit."""

        if (self._mode == PROP_MODE_SERIAL):
            self._serial.close()
        elif (self._mode == PROP_MODE_TCP):
            self._socket.close()
        elif (self._mode == PROP_MODE_FILE):
            self._file.close()