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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 _message_to_string(message, data=None):
 """ Gives a string representation of a PB2 message. """

    if data is None:
        data = _json_from_message(message)

    return "Message {} from {} to {}: {}".format(
        message.namespace, message.source_id, message.destination_id, data)