OK I figured out what my problem was. In my kernel python code I was
setting up the comm channel with these two lines of code.
display(Javascript("""require(["nbextensions/vpython_libraries/glowcomm"],
function(){console.log("GLOWCOMM LOADED");})"""))
comm = Comm(target_name='my_comm_target')
The first line would run javascript code which in turn registered the
target on the javascript front end. The second line would connect to the
target from the python side. If I put a time delay between these two
commands then the problem goes away because the javascript code has time to
execute to register the target to which I am trying to connect the Comm
channel to.
Is there an alternative approach to ensure that the javascript file I
require is loaded when the notebook is opened?
John
On Wednesday, November 22, 2017 at 4:10:37 PM UTC-8, Jason Grout wrote:
>
> Can you turn on the browser debugger and have it pause on errors, and see
> what the lines of code are that are giving the problem (what are the lines
> of code, not just the line numbers)? I would probably debug this by also
> putting a breakpoint at the registration function and making sure that was
> working (i.e., step through the code and make sure that an entry was stored
> in the kernel's comm registry). I would also step through the code where
> the error happened and inspect the registry.
>
> For reference, here is where we are registering a target in
> widgetsnbextension:
> https://github.com/jupyter-widgets/ipywidgets/blob/bbfc39ec0f9e49f730d25bc5347d39e18992a54b/widgetsnbextension/src/manager.js#L71
>
>
> Thanks,
>
> Jason
>
>
> On Wed, Nov 22, 2017 at 2:30 PM John <[email protected] <javascript:>>
> wrote:
>
>> Hi
>>
>> I tried opening a Comm from the kernel as described in
>>
>> http://jupyter-notebook.readthedocs.io/en/stable/comms.html
>>
>> And I am getting the error
>>
>> utils.js:910 Could not open comm -- Error: Class my_comm_target not
>> found in registry
>> at utils.js:874
>> at new Promise (<anonymous>)
>> at Object.load_class (utils.js:859)
>> at CommManager.comm_open (comm.js:84)
>> at i (jquery.min.js:4)
>> at Kernel._handle_iopub_message (kernel.js:1223)
>> at Kernel._finish_ws_message (kernel.js:1015)
>> at kernel.js:1006
>> at <anonymous>
>> (anonymous) @ utils.js:910
>> Promise rejected (async)
>> CommManager.comm_open @ comm.js:85
>> i @ jquery.min.js:4
>> Kernel._handle_iopub_message @ kernel.js:1223
>> Kernel._finish_ws_message @ kernel.js:1015
>> (anonymous) @ kernel.js:1006
>> Promise resolved (async)
>> Kernel._handle_ws_message @ kernel.js:1006
>> i @ jquery.min.js:4
>>
>> I have have a custom javascript file called glowcomm.js that is installed
>> at the location
>>
>> nbextensions/vpython_libraries/glowcomm.js
>>
>> The javascript code comes from a python package called vpython that
>> installs some custom javascript code to this location using
>>
>> notebook.nbextensions.install_nbextension(path =
>> package_dir+"/vpython_libraries",overwrite = True,user = True,verbose = 0)
>>
>>
>> The contents of the glowcomm.js file looks like
>>
>> define(["nbextensions/vpython_libraries/jquery-ui.custom.min",
>> "nbextensions/vpython_libraries/glow.min"], function() {
>>
>> var comm
>>
>> IPython.notebook.kernel.comm_manager.register_target('my_comm_target',
>>
>> What do I need to do to register "my_comm_target" so that I don't get
>> this error.
>>
>> Error: Class my_comm_target not found in registry
>>
>>
>>
>> Thanks
>>
>> John
>>
>>
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