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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 attach(self, payload):
 """Add the given payload to the current payload. The current payload will always be a list of objects after this method is called. If you want to set the payload to a scalar object, use set_payload() instead. """

        if self._payload is None:
            self._payload = [payload]
        else:
            self._payload.append(payload)