{"action":"created","issue":{"url":"https://api.github.com/repos/jupyter/jupyterhub/issues/262","labels_url":"https://api.github.com/repos/jupyter/jupyterhub/issues/262/labels{/name}","comments_url":"https://api.github.com/repos/jupyter/jupyterhub/issues/262/comments","events_url":"https://api.github.com/repos/jupyter/jupyterhub/issues/262/events","html_url":"https://github.com/jupyter/jupyterhub/issues/262","id":90567690,"number":262,"title":"Single user server launch is broken","user":{"login":"jhamrick","id":83444,"avatar_url":"https://avatars.githubusercontent.com/u/83444?v=3","gravatar_id":"","url":"https://api.github.com/users/jhamrick","html_url":"https://github.com/jhamrick","followers_url":"https://api.github.com/users/jhamrick/followers","following_url":"https://api.github.com/users/jhamrick/following{/other_user}","gists_url":"https://api.github.com/users/jhamrick/gists{/gist_id}","starred_url":"https://api.github.com/users/jhamrick/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jhamrick/subscriptions","organizations_url":"https://api.github.com/users/jhamrick/orgs","repos_url":"https://api.github.com/users/jhamrick/repos","events_url":"https://api.github.com/users/jhamrick/events{/privacy}","received_events_url":"https://api.github.com/users/jhamrick/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/jupyter/jupyterhub/labels/bug","name":"bug","color":"fc2929"}],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":6,"created_at":"2015-06-24T05:15:45Z","updated_at":"2015-06-24T12:13:37Z","closed_at":null,"body":"I think that #261 broke the launching of the single user server. I am seeing the following errors in the nbgrader tests:\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"/Users/jhamrick/.virtualenvs/nbgrader/bin/jupyterhub-singleuser\", line 6, in <module>\r\n    exec(compile(open(__file__).read(), __file__, 'exec'))\r\n  File \"/Users/jhamrick/project/tools/jupyterhub/scripts/jupyterhub-singleuser\", line 4, in <module>\r\n    main()\r\n  File \"/Users/jhamrick/project/tools/jupyterhub/jupyterhub/singleuser.py\", line 221, in main\r\n    return SingleUserNotebookApp.launch_instance()\r\n  File \"/Users/jhamrick/.virtualenvs/nbgrader/lib/python3.4/site-packages/IPython/config/application.py\", line 573, in launch_instance\r\n    app.initialize(argv)\r\n  File \"<string>\", line 2, in initialize\r\n  File \"/Users/jhamrick/.virtualenvs/nbgrader/lib/python3.4/site-packages/IPython/config/application.py\", line 75, in catch_config_error\r\n    return method(app, *args, **kwargs)\r\n  File \"/Users/jhamrick/.virtualenvs/nbgrader/lib/python3.4/site-packages/IPython/html/notebookapp.py\", line 1015, in initialize\r\n    self.init_webapp()\r\n  File \"/Users/jhamrick/project/tools/jupyterhub/jupyterhub/singleuser.py\", line 191, in init_webapp\r\n    s['user'] = self.user\r\n  File \"/Users/jhamrick/.virtualenvs/nbgrader/lib/python3.4/site-packages/traitlets/traitlets.py\", line 438, in __get__\r\n    % (self.name, obj))\r\ntraitlets.traitlets.TraitError: No default value found for None trait of <jupyterhub.singleuser.SingleUserNotebookApp object at 0x102953b00>\r\n```\r\n\r\nIf I revert to the version of jupyterhub prior to that PR, this error does not occur. @epifanio reported on gitter seeing the same thing as well, so I don't think it's isolated to nbgrader.\r\n\r\nGiven the error message, I suspect this has to do with ipython/traitlets#39 and/or ipython/traitlets#40 though I haven't actually tested it. I tried giving the `user` trait a default value but it did not seem to fix the error. I will try to do a bit more debugging, but I fear I don't really understand the internals of traitlets well enough to know exactly what's going on here.\r\n\r\nPing @takluyver and @minrk ?"},"comment":{"url":"https://api.github.com/repos/jupyter/jupyterhub/issues/comments/114846427","html_url":"https://github.com/jupyter/jupyterhub/issues/262#issuecomment-114846427","issue_url":"https://api.github.com/repos/jupyter/jupyterhub/issues/262","id":114846427,"user":{"login":"jhamrick","id":83444,"avatar_url":"https://avatars.githubusercontent.com/u/83444?v=3","gravatar_id":"","url":"https://api.github.com/users/jhamrick","html_url":"https://github.com/jhamrick","followers_url":"https://api.github.com/users/jhamrick/followers","following_url":"https://api.github.com/users/jhamrick/following{/other_user}","gists_url":"https://api.github.com/users/jhamrick/gists{/gist_id}","starred_url":"https://api.github.com/users/jhamrick/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jhamrick/subscriptions","organizations_url":"https://api.github.com/users/jhamrick/orgs","repos_url":"https://api.github.com/users/jhamrick/repos","events_url":"https://api.github.com/users/jhamrick/events{/privacy}","received_events_url":"https://api.github.com/users/jhamrick/received_events","type":"User","site_admin":false},"created_at":"2015-06-24T12:13:37Z","updated_at":"2015-06-24T12:13:37Z","body":"Yeah, it seemed to me like it had to do with `name` not ever being set -- but I should think that it would be set in this case, because based on my understanding of traitlets, `name` should always be set if the trait is an attribute of an object that inherits from `HasTraits`. But I don't know why it's not being set, then, because `SingleUserNotebookApp` does inherit from `HasTraits` -- and when I looked at the traitlets source, I couldn't actually find any instances of `name` being set anywhere. I think there is probably some fancy metaclass magic going on somewhere that sets it, but at least at 2am last night I was unable to track it down :-)"}}