From 1445a8d4d6df3a216519f358ad3163c72f7fe02c Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Fri, 30 Jan 2026 13:12:22 +0100
Subject: [PATCH] gh-140824: Fix _Py_DumpExtensionModules() to ignore
 sub-modules

Ignore "math.integer" extension if "math" is in
sys.stdlib_module_names.
---
 Lib/test/test_faulthandler.py                 | 17 +++++++++++++-
 ...-01-30-13-23-06.gh-issue-140824.J1OCrC.rst |  3 +++
 Python/pylifecycle.c                          | 23 +++++++++++++++----
 3 files changed, 37 insertions(+), 6 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-01-30-13-23-06.gh-issue-140824.J1OCrC.rst

diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index 874f52af857b94..9d6a787d2bec27 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -388,9 +388,11 @@ def test_disable(self):
 
     @skip_segfault_on_android
     def test_dump_ext_modules(self):
+        # Disable sys.stdlib_module_names
         code = """
             import faulthandler
             import sys
+            import math
             # Don't filter stdlib module names
             sys.stdlib_module_names = frozenset()
             faulthandler.enable()
@@ -403,9 +405,22 @@ def test_dump_ext_modules(self):
         if not match:
             self.fail(f"Cannot find 'Extension modules:' in {stderr!r}")
         modules = set(match.group(1).strip().split(', '))
-        for name in ('sys', 'faulthandler'):
+        for name in ('sys', 'faulthandler', 'math'):
             self.assertIn(name, modules)
 
+        # Ignore "math.integer" sub-module if "math" package is
+        # in sys.stdlib_module_names
+        code = """
+            import faulthandler
+            import math.integer
+            faulthandler.enable()
+            faulthandler._sigsegv()
+            """
+        stderr, exitcode = self.get_output(code)
+        stderr = '\n'.join(stderr)
+        match = re.search(r'^Extension modules:', stderr, re.MULTILINE)
+        self.assertIsNone(match)
+
     def test_is_enabled(self):
         orig_stderr = sys.stderr
         try:
diff --git a/Misc/NEWS.d/next/Library/2026-01-30-13-23-06.gh-issue-140824.J1OCrC.rst b/Misc/NEWS.d/next/Library/2026-01-30-13-23-06.gh-issue-140824.J1OCrC.rst
new file mode 100644
index 00000000000000..43c696f6609c5f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-30-13-23-06.gh-issue-140824.J1OCrC.rst
@@ -0,0 +1,3 @@
+When :mod:`faulthandler` dumps the list of third-party extension modules,
+ignore ``math.integer`` sub-module since ``math`` package is part of
+:data:`sys.stdlib_module_names`. Patch by Victor Stinner.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index d3ed08de1d15d3..70a74acea07207 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -3393,11 +3393,24 @@ _Py_DumpExtensionModules(int fd, PyInterpreterState *interp)
             Py_hash_t hash;
             // if stdlib_module_names is not NULL, it is always a frozenset.
             while (_PySet_NextEntry(stdlib_module_names, &i, &item, &hash)) {
-                if (PyUnicode_Check(item)
-                    && PyUnicode_Compare(key, item) == 0)
-                {
-                    is_stdlib_ext = 1;
-                    break;
+                if (!PyUnicode_Check(item)) {
+                    continue;
+                }
+                Py_ssize_t len = PyUnicode_GET_LENGTH(item);
+                if (PyUnicode_Tailmatch(key, item, 0, len, -1) == 1) {
+                    Py_ssize_t key_len = PyUnicode_GET_LENGTH(key);
+                    if (key_len == len) {
+                        is_stdlib_ext = 1;
+                        break;
+                    }
+                    assert(key_len > len);
+
+                    // Ignore "math.integer" if key starts with "math."
+                    Py_UCS4 ch = PyUnicode_ReadChar(key, len);
+                    if (ch == '.') {
+                        is_stdlib_ext = 1;
+                        break;
+                    }
                 }
             }
             if (is_stdlib_ext) {