jupyter-run: avoid traceback for NoSuchKernel (#994)

* jupyter-run: avoid traceback for NoSuchKernel

NoSuchKernel used to raise during KernelManager instantiation,
but it is now delayed.

Access kernel_spec to ensure it's raised where it will be caught.

Also removes a redundant warning log immediately before raising,
which prevents complete handling of NoSuchError and produces unavoidable duplicate logs.

* call wait_for_ready() in runapp

ensures kernel is ready before running

avoids lost output if iopub isn't connected yet

and shutdown kernel when finished, rather than relying on the kernel shutting itself down

jupyter_client/consoleapp.py

@@ -306,8 +306,11 @@ def init_kernel_manager(self) -> None:
                 parent=self,
                 data_dir=self.data_dir,
             )
+            # access kernel_spec to ensure the NoSuchKernel error is raised
+            # if it's going to be
+            kernel_spec = self.kernel_manager.kernel_spec  # noqa: F841
         except NoSuchKernel:
-            self.log.critical("Could not find kernel %s", self.kernel_name)
+            self.log.critical("Could not find kernel %r", self.kernel_name)
             self.exit(1)  # type:ignore[attr-defined]
 
         self.kernel_manager = t.cast(KernelManager, self.kernel_manager)

jupyter_client/kernelspec.py

@@ -281,7 +281,6 @@ def get_kernel_spec(self, kernel_name: str) -> KernelSpec:
 
         resource_dir = self._find_spec_directory(kernel_name.lower())
         if resource_dir is None:
-            self.log.warning("Kernelspec name %s cannot be found!", kernel_name)
             raise NoSuchKernel(kernel_name)
 
         return self._get_kernel_spec_by_name(kernel_name, resource_dir)

jupyter_client/runapp.py

@@ -3,10 +3,9 @@
 # Distributed under the terms of the Modified BSD License.
 from __future__ import annotations
 
-import queue
+import atexit
 import signal
 import sys
-import time
 import typing as t
 
 from jupyter_core.application import JupyterApp, base_aliases, base_flags
@@ -73,7 +72,8 @@ def initialize(self, argv: list[str] | None = None) -> None:  # type:ignore[over
         super().initialize(argv)
         JupyterConsoleApp.initialize(self)
         signal.signal(signal.SIGINT, self.handle_sigint)
-        self.init_kernel_info()
+        if self.kernel_manager:
+            atexit.register(self.kernel_manager.shutdown_kernel)
 
     def handle_sigint(self, *args: t.Any) -> None:
         """Handle SIGINT."""
@@ -82,28 +82,11 @@ def handle_sigint(self, *args: t.Any) -> None:
         else:
             self.log.error("Cannot interrupt kernels we didn't start.\n")
 
-    def init_kernel_info(self) -> None:
-        """Wait for a kernel to be ready, and store kernel info"""
-        timeout = self.kernel_timeout
-        tic = time.time()
-        self.kernel_client.hb_channel.unpause()
-        msg_id = self.kernel_client.kernel_info()
-        while True:
-            try:
-                reply = self.kernel_client.get_shell_msg(timeout=1)
-            except queue.Empty as e:
-                if (time.time() - tic) > timeout:
-                    msg = "Kernel didn't respond to kernel_info_request"
-                    raise RuntimeError(msg) from e
-            else:
-                if reply["parent_header"].get("msg_id") == msg_id:
-                    self.kernel_info = reply["content"]
-                    return
-
     def start(self) -> None:
         """Start the application."""
         self.log.debug("jupyter run: starting...")
         super().start()
+        self.kernel_client.wait_for_ready(timeout=self.kernel_timeout)
         if self.filenames_to_run:
             for filename in self.filenames_to_run:
                 self.log.debug("jupyter run: executing `%s`", filename)
@@ -112,8 +95,10 @@ def start(self) -> None:
                     reply = self.kernel_client.execute_interactive(code, timeout=OUTPUT_TIMEOUT)
                     return_code = 0 if reply["content"]["status"] == "ok" else 1
                     if return_code:
-                        raise Exception("jupyter-run error running '%s'" % filename)
+                        msg = f"jupyter-run error running '{filename}'"
+                        raise Exception(msg)
         else:
+            self.log.debug("jupyter run: executing from stdin")
             code = sys.stdin.read()
             reply = self.kernel_client.execute_interactive(code, timeout=OUTPUT_TIMEOUT)
             return_code = 0 if reply["content"]["status"] == "ok" else 1

tests/test_runapp.py

@@ -0,0 +1,34 @@
+import sys
+from subprocess import run
+
+
+def test_runapp(tmp_path):
+    test_py = tmp_path / "test.py"
+    with test_py.open("w") as f:
+        f.write("print('hello')")
+
+    p = run(
+        [sys.executable, "-m", "jupyter_client.runapp", str(test_py)],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    assert p.stdout.strip() == "hello"
+
+
+def test_no_such_kernel(tmp_path):
+    test_py = tmp_path / "test.py"
+    with test_py.open("w") as f:
+        f.write("print('hello')")
+    kernel_name = "nosuchkernel"
+    p = run(
+        [sys.executable, "-m", "jupyter_client.runapp", "--kernel", kernel_name, str(test_py)],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    assert p.returncode
+    assert "Could not find kernel" in p.stderr
+    assert kernel_name in p.stderr
+    # shouldn't show a traceback
+    assert "Traceback" not in p.stderr