Remove resolved names from sys.lazy_modules consistently

Names only left sys.lazy_modules through _imp._set_lazy_attributes(), which
the import machinery calls from _find_and_load_unlocked(). Two cases never
reached it, so their names were recorded and then kept forever:

- A lazy import of a module already in sys.modules. _find_and_load() returns
  early, so nothing ever discards the name. Do not record it in the first
  place.

- The "pkg.attr" entry for `lazy from pkg import attr`. The import machinery
  only discards module names, and attr is often not a module. Discard it when
  the lazy object is reified, where the name is already known and has been
  resolved either way.

Submodules that are not yet loaded are still tracked: loading a package does
not load its submodules, so those imports can still fire. Names whose
reification failed also stay tracked, since the import can still happen.

Author: brittanyrey

Lib/test/test_lazy_import/__init__.py

@@ -53,7 +53,8 @@ def test_sys_lazy_modules(self):
             self.fail('lazy import failed')
 
         self.assertFalse("test.test_lazy_import.data.basic2" in sys.modules)
-        self.assertIn("test.test_lazy_import.data", sys.lazy_modules)
+        # The package is already loaded, so it is not a pending import.
+        self.assertNotIn("test.test_lazy_import.data", sys.lazy_modules)
         self.assertIn("test.test_lazy_import.data.basic2", sys.lazy_modules)
         test.test_lazy_import.data.basic_from_unused.basic2
         self.assertNotIn("test.test_import.data", sys.lazy_modules)
@@ -1275,6 +1276,103 @@ def test_lazy_module_without_children_is_tracked(self):
         """)
         assert_python_ok("-c", code)
 
+    def test_already_loaded_module_is_not_tracked(self):
+        """A lazy import of an already loaded module should not be tracked."""
+        code = textwrap.dedent("""
+            import sys
+
+            # Loaded by a regular import.
+            import json
+            lazy import json as lazy_json
+            assert "json" not in sys.lazy_modules, (
+                f"expected 'json' not in sys.lazy_modules, got {sys.lazy_modules}"
+            )
+
+            # Loaded by reifying an earlier lazy import.
+            lazy import base64
+            _ = base64.b64encode
+            lazy import base64 as lazy_base64
+            assert "base64" not in sys.lazy_modules, (
+                f"expected 'base64' not in sys.lazy_modules, got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
+    def test_already_loaded_submodule_is_not_tracked(self):
+        """`lazy from` a loaded submodule should not be tracked either."""
+        code = textwrap.dedent("""
+            import sys
+            import test.test_lazy_import.data.pkg.b
+            lazy from test.test_lazy_import.data.pkg import b
+            assert "test.test_lazy_import.data.pkg.b" not in sys.lazy_modules, (
+                f"expected 'pkg.b' untracked, got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
+    def test_attribute_entry_removed_on_reification(self):
+        """`lazy from x import attr` should untrack "x.attr" once resolved."""
+        code = textwrap.dedent("""
+            import sys
+            lazy from test.test_lazy_import.data.basic2 import x
+            assert "test.test_lazy_import.data.basic2.x" in sys.lazy_modules, (
+                f"expected 'basic2.x' tracked, got {sys.lazy_modules}"
+            )
+            _ = x
+            assert "test.test_lazy_import.data.basic2.x" not in sys.lazy_modules, (
+                f"expected 'basic2.x' untracked, got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
+    def test_failed_reification_stays_tracked(self):
+        """A lazy import that fails to resolve must stay tracked."""
+        code = textwrap.dedent("""
+            import sys
+            lazy import test.test_lazy_import.data.broken_module
+            try:
+                _ = test.test_lazy_import.data.broken_module
+            except ValueError:
+                pass
+            else:
+                raise AssertionError("ValueError was not raised")
+            assert "test.test_lazy_import.data.broken_module" in sys.lazy_modules, (
+                f"failed reification must stay tracked, got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
+    def test_blocked_module_is_still_tracked(self):
+        """A ``None`` entry in sys.modules must not count as loaded."""
+        code = textwrap.dedent("""
+            import sys
+            sys.modules['test.test_lazy_import.data.basic2'] = None
+            lazy import test.test_lazy_import.data.basic2
+            assert "test.test_lazy_import.data.basic2" in sys.lazy_modules, (
+                f"blocked module must stay tracked, got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
+    def test_pending_submodule_is_still_tracked(self):
+        """`lazy from` a submodule that is not loaded must stay tracked."""
+        code = textwrap.dedent("""
+            import sys
+            lazy from test.test_lazy_import.data.pkg import b
+            assert "test.test_lazy_import.data.pkg.b" in sys.lazy_modules, (
+                f"expected 'pkg.b' tracked, got {sys.lazy_modules}"
+            )
+            import test.test_lazy_import.data.pkg
+            assert "test.test_lazy_import.data.pkg.b" not in sys.modules, (
+                "loading the package must not load the submodule"
+            )
+            assert "test.test_lazy_import.data.pkg.b" in sys.lazy_modules, (
+                f"loading the package must not untrack the submodule, "
+                f"got {sys.lazy_modules}"
+            )
+        """)
+        assert_python_ok("-c", code)
+
 
 @support.requires_subprocess()
 class CommandLineAndEnvVarTests(unittest.TestCase):

Misc/NEWS.d/next/Core_and_Builtins/2026-09-16-15-02-11.gh-issue-155695.Kf3xQa.rst

@@ -0,0 +1,3 @@
+Resolved names are now removed from :data:`sys.lazy_modules` more
+consistently: a lazy import of an already loaded module is no longer recorded,
+and reifying ``lazy from pkg import attr`` now discards the ``pkg.attr`` entry.

Python/import.c

@@ -3917,6 +3917,20 @@ lazy_import_replay_from(PyThreadState *tstate, PyObject *mod,
     return obj;
 }
 
+// The import machinery only discards module names, so this is what removes
+// the "pkg.attr" entry left by `lazy from pkg import attr`, submodule or not.
+static int
+discard_reified_lazy_import(PyInterpreterState *interp, PyObject *lazy_import)
+{
+    PyObject *name = _PyLazyImport_GetName(lazy_import);
+    if (name == NULL) {
+        return -1;
+    }
+    int res = PySet_Discard(LAZY_MODULES(interp), name);
+    Py_DECREF(name);
+    return res < 0 ? -1 : 0;
+}
+
 PyObject *
 _PyImport_LoadLazyImportTstate(PyThreadState *tstate, PyObject *lazy_import)
 {
@@ -4100,6 +4114,10 @@ _PyImport_LoadLazyImportTstate(PyThreadState *tstate, PyObject *lazy_import)
     }
 
 ok:
+    if (obj != NULL && discard_reified_lazy_import(interp, lazy_import) < 0) {
+        Py_CLEAR(obj);
+    }
+
     if (PySet_Discard(importing, lazy_import) < 0) {
         Py_CLEAR(obj);
     }
@@ -4358,6 +4376,27 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
     return final_mod;
 }
 
+// Check if a module is already loaded before adding it to sys.lazy_modules
+static int
+lazy_modules_add(PyThreadState *tstate, PyObject *name)
+{
+    PyObject *modules = get_modules_dict(tstate, false);
+    if (modules == NULL) {
+        return -1;
+    }
+    PyObject *existing;
+    if (PyDict_GetItemRef(modules, name, &existing) < 0) {
+        return -1;
+    }
+    // A None entry blocks the import rather than satisfying it.
+    int loaded = (existing != NULL && existing != Py_None);
+    Py_XDECREF(existing);
+    if (loaded) {
+        return 0;
+    }
+    return PySet_Add(LAZY_MODULES(tstate->interp), name);
+}
+
 // ensure we have the set for the parent module name in sys.lazy_modules.
 // Returns a new reference.
 static PyObject *
@@ -4451,9 +4490,7 @@ register_from_lazy_on_parent(PyThreadState *tstate, PyObject *abs_name,
         return -1;
     }
 
-    // Add the module name to sys.lazy_modules set (PEP 810).
-    PyObject *lazy_modules = LAZY_MODULES(tstate->interp);
-    if (PySet_Add(lazy_modules, fromname) < 0) {
+    if (lazy_modules_add(tstate, fromname) < 0) {
         Py_DECREF(fromname);
         return -1;
     }
@@ -4627,9 +4664,7 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
         return NULL;
     }
 
-    // Add the module name to sys.lazy_modules set (PEP 810).
-    PyObject *lazy_modules = LAZY_MODULES(tstate->interp);
-    if (PySet_Add(lazy_modules, abs_name) < 0) {
+    if (lazy_modules_add(tstate, abs_name) < 0) {
         goto error;
     }