[IPython-dev] Can I safely ignore "comm_open" for ipywidgets.CommInfo/ipython.widgets

Jonathan Frederic jon.freder at gmail.com
Wed Nov 18 13:18:30 EST 2015

Hi Tom,

If you don't plan on implementing ipywidget support in your kernel, you
shouldn't have to worry about implementing that.  It's a channel used to
determine what widget comms existing in the backend in order to reconnect
them to the front end on page refresh.

Regarding "target_name key is not found on the receiving side", I suggest
you read the comm spec here:
https://github.com/ipython/ipython/wiki/IPEP-21%3A-Widget-Messages .
Basically comm handlers are registered by target_name, that's how the comms
are matched accross the front end / back end boundary.


On Wed, Nov 18, 2015 at 8:43 AM, Tom Quarendon <tom.quarendon at teamwpc.co.uk>

> When we run our kernel from a notebook the kernel gets a “comm_open”
> request with widget class “ipywidgets.CommInfo”, target name
> “ipython.widgets”.
> What do we do with this?
> Can I safely ignore this message and any other comm_open messages? Should
> I respond to any comm_open messages with a comm_close as suggested in the
> docs (“If the target_name key is not found on the receiving side, then it
> should immediately reply with a comm_close message to avoid an inconsistent
> state.” But it’s unclear what the “target_name key is not found on the
> receiving side” means).
> Thanks.
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