Nicer error message when kernel is not found

IPython/consoleapp.py

@@ -35,6 +35,7 b' from IPython.core.profiledir import ProfileDir'
 from IPython.kernel.blocking import BlockingKernelClient
 from IPython.kernel import KernelManager
 from IPython.kernel import tunnel_to_kernel, find_connection_file, swallow_argv
+from IPython.kernel.kernelspec import NoSuchKernel
 from IPython.utils.path import filefind
 from IPython.utils.py3compat import str_to_bytes
 from IPython.utils.traitlets import (
@@ -331,18 +332,23 b' class IPythonConsoleApp(ConnectionFileMixin):'
         signal.signal(signal.SIGINT, signal.SIG_DFL)
 
         # Create a KernelManager and start a kernel.
-        self.kernel_manager = self.kernel_manager_class(
-                                ip=self.ip,
-                                transport=self.transport,
-                                shell_port=self.shell_port,
-                                iopub_port=self.iopub_port,
-                                stdin_port=self.stdin_port,
-                                hb_port=self.hb_port,
-                                connection_file=self.connection_file,
-                                kernel_name=self.kernel_name,
-                                parent=self,
-                                ipython_dir=self.ipython_dir,
-        )
+        try:
+            self.kernel_manager = self.kernel_manager_class(
+                                    ip=self.ip,
+                                    transport=self.transport,
+                                    shell_port=self.shell_port,
+                                    iopub_port=self.iopub_port,
+                                    stdin_port=self.stdin_port,
+                                    hb_port=self.hb_port,
+                                    connection_file=self.connection_file,
+                                    kernel_name=self.kernel_name,
+                                    parent=self,
+                                    ipython_dir=self.ipython_dir,
+            )
+        except NoSuchKernel:
+            self.log.critical("Could not find kernel %s", self.kernel_name)
+            self.exit(1)
+
         self.kernel_manager.client_factory = self.kernel_client_class
         self.kernel_manager.start_kernel(extra_arguments=self.kernel_argv)
         atexit.register(self.kernel_manager.cleanup_ipc_files)

IPython/kernel/kernelspec.py

@@ -62,6 +62,10 b' def _list_kernels_in(dir):'
     return {f.lower(): pjoin(dir, f) for f in os.listdir(dir)
                         if _is_kernel_dir(pjoin(dir, f))}
 
+class NoSuchKernel(KeyError):
+    def __init__(self, name):
+        self.name = name
+
 class KernelSpecManager(HasTraits):
     ipython_dir = Unicode()
     def _ipython_dir_default(self):
@@ -115,12 +119,15 b' class KernelSpecManager(HasTraits):'
     def get_kernel_spec(self, kernel_name):
         """Returns a :class:`KernelSpec` instance for the given kernel_name.
         
-        Raises KeyError if the given kernel name is not found.
+        Raises :exc:`NoSuchKernel` if the given kernel name is not found.
         """
         if kernel_name == 'python':
             kernel_name = NATIVE_KERNEL_NAME
         d = self.find_kernel_specs()
-        resource_dir = d[kernel_name.lower()]
+        try:
+            resource_dir = d[kernel_name.lower()]
+        except KeyError:
+            raise NoSuchKernel(kernel_name)
         return KernelSpec.from_resource_dir(resource_dir)
 
 def find_kernel_specs():