10.2.34 MySQLConnection.start_transaction() Method

This method starts a transaction. It accepts arguments indicating whether to use a consistent snapshot, which transaction isolation level to use, and the transaction access mode:

cnx.start_transaction(consistent_snapshot=bool,
                      isolation_level=level,
                      readonly=access_mode)

The default consistent_snapshot value is False. If the value is True, Connector/Python sends WITH CONSISTENT SNAPSHOT with the statement. MySQL ignores this for isolation levels for which that option does not apply.

The default isolation_level value is None, and permitted values are 'READ UNCOMMITTED', 'READ COMMITTED', 'REPEATABLE READ', and 'SERIALIZABLE'. If the isolation_level value is None, no isolation level is sent, so the default level applies.

The readonly argument can be True to start the transaction in READ ONLY mode or False to start it in READ WRITE mode. If readonly is omitted, the server's default access mode is used. For details about transaction access mode, see the description for the START TRANSACTION statement at START TRANSACTION, COMMIT, and ROLLBACK Statements. If the server is older than MySQL 5.6.5, it does not support setting the access mode and Connector/Python raises a ValueError.

Invoking start_transaction() raises a ProgrammingError if invoked while a transaction is currently in progress. This differs from executing a START TRANSACTION SQL statement while a transaction is in progress; the statement implicitly commits the current transaction.

To determine whether a transaction is active for the connection, use the in_transaction property.

start_transaction() was added in MySQL Connector/Python 1.1.0. The readonly argument was added in Connector/Python 1.1.5.