> For the complete documentation index, see [llms.txt](https://learn.pyblish.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learn.pyblish.com/21-callback-ii.md).

# Callback II

You can emit and catch your own signals.

```python
import pyblish.api

class MyCollector(pyblish.api.ContextPlugin):
    order = pyblish.api.CollectorOrder

    def process(self, context):
        pyblish.api.emit("myEvent", data="myData")
```

You can then catch this signal anywhere in your program.

```python
import pyblish.api

def on_my_event(data):
  print(data)

pyblish.api.register_callback("myEvent", on_my_event)
```

Callbacks can be useful for, amongst other things:

* Deep customisation
* Advanced logging
* Tighter integration

On a technical note, callbacks are run on the main thread and block until finished. This means that if for example one of your callbacks would take 10 seconds to finish, publishing overall will take 10 seconds longer. On the upside, it also means that the Context will accurately reflect the current state at the time of a signal emitting.


---

# 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 dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://learn.pyblish.com/21-callback-ii.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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.