> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/server-programming/pl-python-python-procedural-language-1/trigger-functions.md).

# 46.5. 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.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.postgresql.tw/server-programming/pl-python-python-procedural-language-1/trigger-functions.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.