From 4538894162011b3eeb43e4a86e6f15bc076067a1 Mon Sep 17 00:00:00 2001
From: wpk-nist-gov <wpk@nist.gov>
Date: Mon, 24 Feb 2025 16:37:34 -0500
Subject: [PATCH] feat: added `--missing` flag to list and remove subcommands

---
 jupyter_client/kernelspecapp.py | 51 +++++++++++++++++++++++++++++++--
 tests/test_kernelspecapp.py     |  5 ++++
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/jupyter_client/kernelspecapp.py b/jupyter_client/kernelspecapp.py
index 186aa9cf..37acfa55 100644
--- a/jupyter_client/kernelspecapp.py
+++ b/jupyter_client/kernelspecapp.py
@@ -8,6 +8,7 @@
 import os.path
 import sys
 import typing as t
+from pathlib import Path
 
 from jupyter_core.application import JupyterApp, base_aliases, base_flags
 from traitlets import Bool, Dict, Instance, List, Unicode
@@ -29,12 +30,20 @@ class ListKernelSpecs(JupyterApp):
         help="output spec name and location as machine-readable json.",
         config=True,
     )
-
+    missing_kernels = Bool(
+        False,
+        help="List only specs with missing interpreters.",
+        config=True,
+    )
     flags = {
         "json": (
             {"ListKernelSpecs": {"json_output": True}},
             "output spec name and location as machine-readable json.",
         ),
+        "missing": (
+            {"ListKernelSpecs": {"missing_kernels": True}},
+            "output only missing kernels",
+        ),
         "debug": base_flags["debug"],
     }
 
@@ -45,6 +54,10 @@ def start(self) -> dict[str, t.Any] | None:  # type:ignore[override]
         """Start the application."""
         paths = self.kernel_spec_manager.find_kernel_specs()
         specs = self.kernel_spec_manager.get_all_specs()
+
+        if self.missing_kernels:
+            paths, specs = _limit_to_missing(paths, specs)
+
         if not self.json_output:
             if not specs:
                 print("No kernels available")
@@ -177,6 +190,11 @@ class RemoveKernelSpec(JupyterApp):
 
     force = Bool(False, config=True, help="""Force removal, don't prompt for confirmation.""")
     spec_names = List(Unicode())
+    missing_kernels = Bool(
+        False,
+        help="Remove missing specs.",
+        config=True,
+    )
 
     kernel_spec_manager = Instance(KernelSpecManager)
 
@@ -185,6 +203,10 @@ def _kernel_spec_manager_default(self) -> KernelSpecManager:
 
     flags = {
         "f": ({"RemoveKernelSpec": {"force": True}}, force.help),
+        "missing": (
+            {"RemoveKernelSpec": {"missing_kernels": True}},
+            "remove missing kernels",
+        ),
     }
     flags.update(JupyterApp.flags)
 
@@ -195,12 +217,22 @@ def parse_command_line(self, argv: list[str] | None) -> None:  # type:ignore[ove
         if self.extra_args:
             self.spec_names = sorted(set(self.extra_args))  # remove duplicates
         else:
-            self.exit("No kernelspec specified.")
+            self.spec_names = []
 
     def start(self) -> None:
         """Start the application."""
         self.kernel_spec_manager.ensure_native_kernel = False
         spec_paths = self.kernel_spec_manager.find_kernel_specs()
+
+        if self.missing_kernels:
+            _, spec = _limit_to_missing(
+                spec_paths,
+                self.kernel_spec_manager.get_all_specs(),
+            )
+
+            # append missing kernels
+            self.spec_names = sorted(set(self.spec_names + list(spec)))
+
         missing = set(self.spec_names).difference(set(spec_paths))
         if missing:
             self.exit("Couldn't find kernel spec(s): %s" % ", ".join(missing))
@@ -337,5 +369,20 @@ def start(self) -> None:
             return self.subapp.start()
 
 
+def _limit_to_missing(
+    paths: dict[str, str], specs: dict[str, t.Any]
+) -> tuple[dict[str, str], dict[str, t.Any]]:
+    specs_: dict[str, t.Any] = {
+        k: v
+        for k, v in specs.items()
+        # If have kernel installed from current environment
+        # Probably not the best way to do this, but it works in edge cases I've run into.
+        if (prog := v["spec"]["argv"][0]) != "python" and not Path(prog).exists()
+    }
+
+    paths_: dict[str, str] = {k: v for k, v in paths.items() if k in specs_}
+    return paths_, specs_
+
+
 if __name__ == "__main__":
     KernelSpecApp.launch_instance()
diff --git a/tests/test_kernelspecapp.py b/tests/test_kernelspecapp.py
index 119b6fb6..85cb7a8e 100644
--- a/tests/test_kernelspecapp.py
+++ b/tests/test_kernelspecapp.py
@@ -38,6 +38,11 @@ def test_kernelspec_sub_apps(jp_kernel_dir):
     specs = app3.start()
     assert specs and "echo" not in specs
 
+    app4 = ListKernelSpecs(missing_kernels=True)
+    app4.kernel_spec_manager.kernel_dirs.append(kernel_dir)
+    specs = app4.start()
+    assert specs is None
+
 
 def test_kernelspec_app():
     app = KernelSpecApp()