PL/Python can be used to define trigger functions.PostgreSQL requires that a function that is to be called as a trigger must be declared as a function with no arguments and a return type oftrigger.
When a function is used as a trigger, the dictionaryTD contains trigger-related values:
TD["event"]contains the event as a string:INSERT,UPDATE,DELETE, orTRUNCATE.
TD["when"]contains one ofBEFORE,AFTER, orINSTEAD OF.
TD["level"]containsROW orSTATEMENT.
TD["new"]TD["old"]For a row-level trigger, one or both of these fields contain the respective trigger rows, depending on the trigger event.
TD["name"]contains the trigger name.
TD["table_name"]contains the name of the table on which the trigger occurred.
TD["table_schema"]contains the schema of the table on which the trigger occurred.
TD["relid"]contains the OID of the table on which the trigger occurred.
TD["args"]If theCREATE TRIGGER command included arguments, they are available inTD["args"][0] toTD["args"][.n-1]
IfTD["when"] isBEFORE orINSTEAD OF andTD["level"] isROW, you can returnNone or"OK" from the Python function to indicate the row is unmodified,"SKIP" to abort the event, or ifTD["event"] isINSERT orUPDATE you can return"MODIFY" to indicate you've modified the new row. Otherwise the return value is ignored.