Handle NoSuchKernel errors more gracefully

IPython/html/services/sessions/handlers.py

@@ -1,113 +1,118 b''
 """Tornado handlers for the sessions web service."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import json
 
 from tornado import web
 
 from ...base.handlers import IPythonHandler, json_errors
 from IPython.utils.jsonutil import date_default
 from IPython.html.utils import url_path_join, url_escape
+from IPython.kernel.kernelspec import NoSuchKernel
 
 
 class SessionRootHandler(IPythonHandler):
 
     @web.authenticated
     @json_errors
     def get(self):
         # Return a list of running sessions
         sm = self.session_manager
         sessions = sm.list_sessions()
         self.finish(json.dumps(sessions, default=date_default))
 
     @web.authenticated
     @json_errors
     def post(self):
         # Creates a new session
         #(unless a session already exists for the named nb)
         sm = self.session_manager
         cm = self.contents_manager
         km = self.kernel_manager
 
         model = self.get_json_body()
         if model is None:
             raise web.HTTPError(400, "No JSON data provided")
         try:
             name = model['notebook']['name']
         except KeyError:
             raise web.HTTPError(400, "Missing field in JSON data: notebook.name")
         try:
             path = model['notebook']['path']
         except KeyError:
             raise web.HTTPError(400, "Missing field in JSON data: notebook.path")
         try:
             kernel_name = model['kernel']['name']
         except KeyError:
             self.log.debug("No kernel name specified, using default kernel")
             kernel_name = None
 
         # Check to see if session exists
         if sm.session_exists(name=name, path=path):
             model = sm.get_session(name=name, path=path)
         else:
+            try:
             model = sm.create_session(name=name, path=path, kernel_name=kernel_name)
+            except NoSuchKernel:
+                raise web.HTTPError(400, "No such kernel: %s" % kernel_name)
+
         location = url_path_join(self.base_url, 'api', 'sessions', model['id'])
         self.set_header('Location', url_escape(location))
         self.set_status(201)
         self.finish(json.dumps(model, default=date_default))
 
 class SessionHandler(IPythonHandler):
 
     SUPPORTED_METHODS = ('GET', 'PATCH', 'DELETE')
 
     @web.authenticated
     @json_errors
     def get(self, session_id):
         # Returns the JSON model for a single session
         sm = self.session_manager
         model = sm.get_session(session_id=session_id)
         self.finish(json.dumps(model, default=date_default))
 
     @web.authenticated
     @json_errors
     def patch(self, session_id):
         # Currently, this handler is strictly for renaming notebooks
         sm = self.session_manager
         model = self.get_json_body()
         if model is None:
             raise web.HTTPError(400, "No JSON data provided")
         changes = {}
         if 'notebook' in model:
             notebook = model['notebook']
             if 'name' in notebook:
                 changes['name'] = notebook['name']
             if 'path' in notebook:
                 changes['path'] = notebook['path']
 
         sm.update_session(session_id, **changes)
         model = sm.get_session(session_id=session_id)
         self.finish(json.dumps(model, default=date_default))
 
     @web.authenticated
     @json_errors
     def delete(self, session_id):
         # Deletes the session with given session_id
         sm = self.session_manager
         sm.delete_session(session_id)
         self.set_status(204)
         self.finish()
 
 
 #-----------------------------------------------------------------------------
 # URL to handler mappings
 #-----------------------------------------------------------------------------
 
 _session_id_regex = r"(?P<session_id>\w+-\w+-\w+-\w+-\w+)"
 
 default_handlers = [
     (r"/api/sessions/%s" % _session_id_regex, SessionHandler),
     (r"/api/sessions",  SessionRootHandler)
 ]