It doesn't actually print the source.

James William Pye · James William Pye · commit 6c94b201deea · 2009-04-03T05:07:33.000-07:00
diff --git a/postgresql/documentation/driver.py b/postgresql/documentation/driver.py
@@ -1291,7 +1291,6 @@
 	postgresql.exceptions.InFailedTransactionError: invalid block exit detected
 	CODE: 25P02
 	SEVERITY: ERROR
-	SOURCE: CLIENT
 
 Normally, if a ``COMMIT`` is issued on a failed transaction, the command implies a
 ``ROLLBACK`` without error. This is a very undesirable result for the CM's exit
