PostgreSQL 9.6.5 Documentation
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44.6. Trigger Functions

When a function is used as a trigger, the dictionary TD contains trigger-related values:

TD["event"]

contains the event as a string: INSERT, UPDATE, DELETE, or TRUNCATE.

TD["when"]

contains one of BEFORE, AFTER, or INSTEAD OF.

TD["level"]

contains ROW or STATEMENT.

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 the CREATE TRIGGER command included arguments, they are available in TD["args"][0] to TD["args"][n-1].

If TD["when"] is BEFORE or INSTEAD OF and TD["level"] is ROW, you can return None or "OK" from the Python function to indicate the row is unmodified, "SKIP" to abort the event, or if TD["event"] is INSERT or UPDATE you can return "MODIFY" to indicate you've modified the new row. Otherwise the return value is ignored.

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