Submit the batch, returning the JSON->dict from the last HTTP response

def _submit_batch(self, url, batch):
        """Submit the batch, returning the JSON->dict from the last HTTP response"""
        # TODO: validate column_name
        batch_parts = batch.parts()

        guid = ""
        headers = {
            'User-Agent': 'kentik-python-api/0.1',
            'Content-Type': 'application/json',
            'X-CH-Auth-Email': self.api_email,
            'X-CH-Auth-API-Token': self.api_token
        }

        # submit each part
        last_part = dict()
        for batch_part in batch_parts:
            # submit
            resp = requests.post(url, headers=headers, data=batch_part.build_json(guid))

            # print the HTTP response to help debug
            print(resp.text)

            # break out at first sign of trouble
            resp.raise_for_status()
            last_part = resp.json()
            guid = last_part['guid']
            if guid is None or len(guid) == 0:
                raise RuntimeError('guid not found in batch response')

        return last_part