Method _checkout

pymongo/synchronous/mongo_client.py:1785–1816

(
        self, server: Server, session: Optional[ClientSession]
    )

    @contextlib.contextmanager
    def _checkout(
        self, server: Server, session: Optional[ClientSession]
    ) -> Generator[Connection, None]:
        in_txn = session and session.in_transaction
        with _MongoClientErrorHandler(self, server, session) as err_handler:
            # Reuse the pinned connection, if it exists.
            if in_txn and session and session._pinned_connection:
                err_handler.contribute_socket(session._pinned_connection)
                yield session._pinned_connection
                return
            with server.checkout(handler=err_handler) as conn:
                # Pin this session to the selected server or connection.
                if (
                    in_txn
                    and session
                    and server.description.server_type
                    in (
                        SERVER_TYPE.Mongos,
                        SERVER_TYPE.LoadBalancer,
                    )
                ):
                    session._pin(server, conn)
                err_handler.contribute_socket(conn)
                if (
                    self._encrypter
                    and not self._encrypter._bypass_auto_encryption
                    and conn.max_wire_version < 8
                ):
                    raise ConfigurationError(
                        "Auto-encryption requires a minimum MongoDB version of 4.2"
                    )
                yield conn

    def _select_server(
        self,