def __enter__()

in upload.py [0:0]


    def __enter__(self) -> SessionConfigurator:
        """Initiate a Bigquery session and return the session_id."""
        job = self._bigquery_client.query(
            "SELECT 1;",  # a query that won't fail
            job_config=bigquery.QueryJobConfig(create_session=True),
        )
        assert job.session_info.session_id is not None
        self._session_cfg = SessionConfigurator(job.session_info.session_id)
        job.result()  # wait job completion
        return self._session_cfg