Using Transactions in Python Programs

15.7.1 Problem

You want to perform a transaction in a DB-API script.

15.7.2 Solution

Use the standard DB-API transaction support mechanism.

15.7.3 Discussion

The Python DB-API abstraction provides transaction processing control through connection object methods. Invoke begin( ) to begin a transaction and either commit( ) or rollback( ) to end it. The begin( ) and commit( ) calls go into a try block, and the rollback( ) goes into the corresponding except block to cancel the transaction if an error occurs:

try: conn.begin ( ) cursor = conn.cursor ( ) # move some money from one person to the other cursor.execute ("UPDATE money SET amt = amt - 6 WHERE name = 'Eve'") cursor.execute ("UPDATE money SET amt = amt + 6 WHERE name = 'Ida'") cursor.close ( ) conn.commit( ) except MySQLdb.Error, e: print "Transaction failed, rolling back. Error was:" print e.args try: # empty exception handler in case rollback fails conn.rollback ( ) except: pass