This property returns True or False to indicate whether a transaction is active for the connection. The value is True regardless of whether you start a transaction using the start_transaction() API call or by directly executing an SQL statement such as START TRANSACTION or BEGIN.

>>> cnx.start_transaction()
>>> cnx.in_transaction
True
>>> cnx.commit()
>>> cnx.in_transaction
False

in_transaction was added in MySQL Connector/Python 1.1.0.