---
title: "Event Trigger Functions"
id: plpython-event-trigger
pg_version: "20devel"
---

<a id="plpython-event-trigger"></a>

## 44.6. Event Trigger Functions

PL/Python can be used to define event triggers (see also [Chapter 38](event-triggers.md)). PostgreSQL requires that a function that is to be called as an event trigger must be declared as a function with no arguments and a return type of `event_trigger`. 

When a function is used as an event trigger, the dictionary `TD` contains trigger-related values: **`TD["event"]`**

 The event the trigger was fired for, as a string, for example `ddl_command_start`. **`TD["tag"]`**

 The command tag for which the trigger was fired, as a string, for example `DROP TABLE`.  

[Example 44.1](plpython-event-trigger.md#plpython-event-trigger-example) shows an example of an event trigger function in PL/Python. 

<a id="plpython-event-trigger-example"></a>

**A PL/Python Event Trigger Function**

This example trigger simply raises a `NOTICE` message each time a supported command is executed. 


CREATE OR REPLACE FUNCTION pysnitch() RETURNS event_trigger
LANGUAGE plpython3u
AS $$
  plpy.notice("TD[event] => " + TD["event"] + " ; TD[tag] => " + TD["tag"]);
$$;

CREATE EVENT TRIGGER pysnitch ON ddl_command_start EXECUTE FUNCTION pysnitch();