Allow setting namespace from command line usage of uuid module

 - This applies to generating version 3 and 5 UUIDs
 - Will correctly bail when invalid UUID is supplied as namespace

Author: sumpygump

Lib/test/test_uuid.py

@@ -1223,6 +1223,29 @@ def test_cli_uuid3_ouputted_with_valid_namespace_and_name(self):
         self.assertEqual(output, str(uuid_output))
         self.assertEqual(uuid_output.version, 3)
 
+    @mock.patch.object(sys, "argv", ["", "-u", "uuid3", "-n", "any UUID", "-N", "python.org"])
+    @mock.patch('sys.stderr', new_callable=io.StringIO)
+    def test_cli_uuid3_with_invalid_namespace(self, mock_err):
+        with self.assertRaises(SystemExit) as cm:
+            self.uuid.main()
+        # Check that exception code is the same as argparse.ArgumentParser.error
+        self.assertEqual(cm.exception.code, 2)
+        self.assertIn("error: badly formed hexadecimal UUID string", mock_err.getvalue())
+
+    @mock.patch.object(sys, "argv",
+                       ["", "-u", "uuid3", "-n", "0d6a16cc-34a7-47d8-b660-214d0ae184d2", "-N", "some.user"])
+    def test_cli_uuid3_ouputted_with_user_provided_namespace_and_name(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            self.uuid.main()
+
+        output = stdout.getvalue().strip()
+        uuid_output = self.uuid.UUID(output)
+
+        # Output should be in the form of uuid5
+        self.assertEqual(output, str(uuid_output))
+        self.assertEqual(uuid_output.version, 3)
+
     @mock.patch.object(sys, "argv",
                        ["", "-u", "uuid5", "-n", "@dns", "-N", "python.org"])
     def test_cli_uuid5_ouputted_with_valid_namespace_and_name(self):
@@ -1237,6 +1260,29 @@ def test_cli_uuid5_ouputted_with_valid_namespace_and_name(self):
         self.assertEqual(output, str(uuid_output))
         self.assertEqual(uuid_output.version, 5)
 
+    @mock.patch.object(sys, "argv", ["", "-u", "uuid5", "-n", "any UUID", "-N", "python.org"])
+    @mock.patch('sys.stderr', new_callable=io.StringIO)
+    def test_cli_uuid5_with_invalid_namespace(self, mock_err):
+        with self.assertRaises(SystemExit) as cm:
+            self.uuid.main()
+        # Check that exception code is the same as argparse.ArgumentParser.error
+        self.assertEqual(cm.exception.code, 2)
+        self.assertIn("error: badly formed hexadecimal UUID string", mock_err.getvalue())
+
+    @mock.patch.object(sys, "argv",
+                       ["", "-u", "uuid5", "-n", "0d6a16cc-34a7-47d8-b660-214d0ae184d2", "-N", "some.user"])
+    def test_cli_uuid5_ouputted_with_user_provided_namespace_and_name(self):
+        stdout = io.StringIO()
+        with contextlib.redirect_stdout(stdout):
+            self.uuid.main()
+
+        output = stdout.getvalue().strip()
+        uuid_output = self.uuid.UUID(output)
+
+        # Output should be in the form of uuid5
+        self.assertEqual(output, str(uuid_output))
+        self.assertEqual(uuid_output.version, 5)
+
     @mock.patch.object(sys, "argv", ["", "-u", "uuid6"])
     def test_cli_uuid6(self):
         self.do_test_standalone_uuid(6)

Lib/uuid.py

@@ -962,7 +962,7 @@ def main():
                         default="uuid4",
                         help="function to generate the UUID")
     parser.add_argument("-n", "--namespace",
-                        choices=["any UUID", *namespaces.keys()],
+                        metavar=f"{{any UUID,{','.join(namespaces.keys())}}}",
                         help="uuid3/uuid5 only: "
                         "a UUID, or a well-known predefined UUID addressed "
                         "by namespace name")
@@ -984,7 +984,15 @@ def main():
                 f"{args.uuid} requires a namespace and a name. "
                 "Run 'python -m uuid -h' for more information."
             )
-        namespace = namespaces[namespace] if namespace in namespaces else UUID(namespace)
+        if namespace in namespaces:
+            namespace = namespaces[namespace]
+        else:
+            try:
+                namespace = UUID(namespace)
+            except ValueError as e:
+                parser.error(
+                    f"{str(e)}: '{args.namespace}'."
+                )
         for _ in range(args.count):
             print(uuid_func(namespace, name))
     else:

Misc/NEWS.d/next/Library/2026-04-18-17-37-13.gh-issue-148740.sYnFi0.rst

@@ -0,0 +1,2 @@
+Fix usage for :mod:`uuid` command line interface to support a custom namespace be
+provided for uuid3 and uuid5.