'Create a new part.'

def _GetPart(self, data, data_type):

    hmac = self.hmac.HMAC(data)
    header = EncryptedHeader(Magic=HEADER_MAGIC, Version=1, PartType=data_type, DataStart=HEADER_SIZE, DataLength=len(data), HMACStart=(HEADER_SIZE + len(data)), HMACLength=len(hmac), PartLength=((HEADER_SIZE + len(hmac)) + len(data)))
    return ((struct.pack(HEADER_FMT, *header) + data) + hmac)
