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