what happened to EventfulList and friends?

[mattvonrocketstein]

in IPython 3.0, I was importing EventfulList like so:

from IPython.utils.traitlets import EventfulList

In IPython 4.0, traitlets is abstracted, which is awesome by the way, but I can't find traitlets.eventful.

What am I missing?

[takluyver]

Eventful was kept with widgets, which is the only thing in IPython that used it:

https://github.com/ipython/ipywidgets/blob/master/ipython_widgets/widgets/eventful.py

[jmsuresh]

I need eventful containers (List, Dict and Set) in my application. The link above is not working. Can anyone suggest what is the recommended module to use now in 2017?

[rmorshea]

@jmsuresh I am unsure of why they were removed. However there is a pull request to implement them again - jupyter-widgets/ipywidgets#1071

[rmorshea]

The above PR uses spectate under the hood:

pip install spectate

Check out the examples and let me know what you think.

[jmsuresh]

Thanks for this. I was trying to test this but could not as it depends on FrozenBunch which is not available in the version I have. Any suggestions?
I am trying to use this eventful container to do a clean MVC pattern for a GUI. I am wondering why there is no popular way to do this as this requirement should be very common.

[rmorshea]

@jmsuresh, I am trying to find time to uncouple the pull request from its dependance on the (as yet) unreleased 5.0 version of traitlets. However even when I do, that branch will probably be unstable since its a WIP and will need to respond to changes during review.

The reason eventful traits haven't been done before is twofold:

1. It's hard and requires a deep knowledge of traitlets to implement (which few people have).
2. It is possible to trigger change notifications if you assign a new instance to the trait.
   • this is obviously not ideal though.