From 105d5517745b3ce4b69acfbabecb96019bac910c Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Tue, 21 Oct 2025 17:18:21 +0100
Subject: [PATCH 01/16] Commit

---
 Lib/traceback.py | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 9b4b8c7d566fe8..2609db1149364d 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1110,7 +1110,11 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
         elif exc_type and issubclass(exc_type, ModuleNotFoundError):
             module_name = getattr(exc_value, "name", None)
             if module_name in sys.stdlib_module_names:
-                self._str = f"Standard library module '{module_name}' was not found"
+                message = _missing_stdlib_module.get(
+                    module_name,
+                    f"Standard library module '{module_name}' was not found"
+                )
+                self._str = message
             elif sys.flags.no_site:
                 self._str += (". Site initialization is disabled, did you forget to "
                     + "add the site-packages directory to sys.path "
@@ -1794,3 +1798,11 @@ def _levenshtein_distance(a, b, max_cost):
             # Everything in this row is too big, so bail early.
             return max_cost + 1
     return result
+
+_windows_only_modules = ["winreg", "msvcrt", "winsound", "nt", "_winapi", "_msi"]
+
+_missing_stdlib_module = {
+    name: f"Windows-only standard library module '{name}' not found"
+    for name in _windows_only_modules
+    # Distributors can patch this dictionary to provide installation suggestions.
+}

From c3d802b9c8f6d002fd40fb2301c0aa8c5fe0595d Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Tue, 21 Oct 2025 18:16:46 +0100
Subject: [PATCH 02/16] Tidy up

---
 Lib/traceback.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 2609db1149364d..7d582adeda0899 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1803,6 +1803,7 @@ def _levenshtein_distance(a, b, max_cost):
 
 _missing_stdlib_module = {
     name: f"Windows-only standard library module '{name}' not found"
-    for name in _windows_only_modules
+    for name in _windows_only_modules,
+} | {
     # Distributors can patch this dictionary to provide installation suggestions.
 }

From 6b2d934544d98781c26c58108ea759e04a0b88c5 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Tue, 21 Oct 2025 18:19:38 +0100
Subject: [PATCH 03/16] Fix up

---
 Lib/traceback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 7d582adeda0899..6d6aa08e296db1 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1803,7 +1803,7 @@ def _levenshtein_distance(a, b, max_cost):
 
 _missing_stdlib_module = {
     name: f"Windows-only standard library module '{name}' not found"
-    for name in _windows_only_modules,
+    for name in _windows_only_modules
 } | {
     # Distributors can patch this dictionary to provide installation suggestions.
 }

From 7f10e66d837c41e71b356ef575019b9ea72533b3 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Wed, 22 Oct 2025 18:07:05 +0100
Subject: [PATCH 04/16] Rework

---
 Lib/traceback.py                       | 27 ++++++++---------
 Makefile.pre.in                        |  2 ++
 Tools/build/check_extension_modules.py | 41 ++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 6d6aa08e296db1..b793449be3ae6e 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -14,6 +14,11 @@
 
 from contextlib import suppress
 
+try:
+    from _stdlib_modules_info import MISSING_STDLIB_MODULE_MESSAGES
+except ImportError:
+    MISSING_STDLIB_MODULE_MESSAGES = None
+
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
            'format_tb', 'print_exc', 'format_exc', 'print_exception',
@@ -1110,11 +1115,14 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
         elif exc_type and issubclass(exc_type, ModuleNotFoundError):
             module_name = getattr(exc_value, "name", None)
             if module_name in sys.stdlib_module_names:
-                message = _missing_stdlib_module.get(
-                    module_name,
-                    f"Standard library module '{module_name}' was not found"
-                )
-                self._str = message
+                if MISSING_STDLIB_MODULE_MESSAGES is not None:
+                    message = MISSING_STDLIB_MODULE_MESSAGES.get(
+                        module_name,
+                        f"Standard library module '{module_name}' was not found"
+                    )
+                    self._str = message
+                else:
+                    self._str = f"Standard library module '{module_name}' was not found"
             elif sys.flags.no_site:
                 self._str += (". Site initialization is disabled, did you forget to "
                     + "add the site-packages directory to sys.path "
@@ -1798,12 +1806,3 @@ def _levenshtein_distance(a, b, max_cost):
             # Everything in this row is too big, so bail early.
             return max_cost + 1
     return result
-
-_windows_only_modules = ["winreg", "msvcrt", "winsound", "nt", "_winapi", "_msi"]
-
-_missing_stdlib_module = {
-    name: f"Windows-only standard library module '{name}' not found"
-    for name in _windows_only_modules
-} | {
-    # Distributors can patch this dictionary to provide installation suggestions.
-}
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 19423c11545c19..ad36ba4b835d9c 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1601,6 +1601,7 @@ sharedmods: $(SHAREDMODS) pybuilddir.txt
 # dependency on BUILDPYTHON ensures that the target is run last
 .PHONY: checksharedmods
 checksharedmods: sharedmods $(PYTHON_FOR_BUILD_DEPS) $(BUILDPYTHON)
+	@$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info
 	@$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py
 
 .PHONY: rundsymutil
@@ -2815,6 +2816,7 @@ libinstall:	all $(srcdir)/Modules/xxmodule.c
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).py $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfig_vars_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).json $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) `cat pybuilddir.txt`/build-details.json $(DESTDIR)$(LIBDEST); \
+	$(INSTALL_DATA) `cat pybuilddir.txt`/_stdlib_modules_info.py $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) $(srcdir)/LICENSE $(DESTDIR)$(LIBDEST)/LICENSE.txt
 	@ # If app store compliance has been configured, apply the patch to the
 	@ # installed library code. The patch has been previously validated against
diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index 668db8df0bd181..f702c360e488aa 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -116,6 +116,12 @@
     help="Print a list of module names to stdout and exit",
 )
 
+parser.add_argument(
+    "--generate-stdlib-info",
+    action="store_true",
+    help="Generate file with stdlib module info",
+)
+
 
 @enum.unique
 class ModuleState(enum.Enum):
@@ -281,6 +287,38 @@ def list_module_names(self, *, all: bool = False) -> set[str]:
             names.update(WINDOWS_MODULES)
         return names
 
+    def generate_stdlib_info(self) -> None:
+
+        disabled_modules = {modinfo.name for modinfo in self.modules
+                           if modinfo.state in (ModuleState.DISABLED, ModuleState.DISABLED_SETUP)}
+        missing_modules = {modinfo.name for modinfo in self.modules
+                          if modinfo.state == ModuleState.MISSING}
+        na_modules = {modinfo.name for modinfo in self.modules
+                     if modinfo.state == ModuleState.NA}
+
+        content = f'''\
+# Standard library information used by the traceback module for more informative
+# ModuleNotFound error messages.
+
+DISABLED_MODULES = {sorted(disabled_modules)!r}
+MISSING_MODULES = {sorted(missing_modules)!r}
+NOT_AVAILABLE_MODULES = {sorted(na_modules)!r}
+WINDOWS_ONLY_MODULES = {sorted(WINDOWS_MODULES)!r}
+
+MISSING_STDLIB_MODULE_MESSAGES = {{
+    **{{name: f"Windows-only standard library module '{{name}}' was not found"
+        for name in WINDOWS_ONLY_MODULES}},
+    **{{name: f"Standard library module disabled during build '{{name}}' was not found"
+        for name in DISABLED_MODULES}},
+    **{{name: f"Unsupported platform for standard library module '{{name}}'"
+        for name in NOT_AVAILABLE_MODULES}},
+}}
+'''
+
+        output_path = self.builddir / "_stdlib_modules_info.py"
+        with open(output_path, "w", encoding="utf-8") as f:
+            f.write(content)
+
     def get_builddir(self) -> pathlib.Path:
         try:
             with open(self.pybuilddir_txt, encoding="utf-8") as f:
@@ -499,6 +537,9 @@ def main() -> None:
         names = checker.list_module_names(all=True)
         for name in sorted(names):
             print(name)
+    elif args.generate_stdlib_info:
+        checker.check()
+        checker.generate_stdlib_info()
     else:
         checker.check()
         checker.summary(verbose=args.verbose)

From a0dd99bec07b1609f5104df868169a94905f6f82 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 23 Oct 2025 16:55:28 +0100
Subject: [PATCH 05/16] Allow passing json file

---
 Makefile.pre.in                        |  6 +++-
 Tools/build/check_extension_modules.py | 39 ++++++++++++++++++--------
 configure                              | 18 ++++++++++++
 configure.ac                           |  9 ++++++
 4 files changed, 59 insertions(+), 13 deletions(-)

diff --git a/Makefile.pre.in b/Makefile.pre.in
index ad36ba4b835d9c..72c623a3d0ed52 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1601,7 +1601,11 @@ sharedmods: $(SHAREDMODS) pybuilddir.txt
 # dependency on BUILDPYTHON ensures that the target is run last
 .PHONY: checksharedmods
 checksharedmods: sharedmods $(PYTHON_FOR_BUILD_DEPS) $(BUILDPYTHON)
-	@$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info
+	@if [ -n "@MISSING_STDLIB_CONFIG@" ]; then \
+		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info="@MISSING_STDLIB_CONFIG@"; \
+	else \
+		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info; \
+	fi
 	@$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py
 
 .PHONY: rundsymutil
diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index f702c360e488aa..f5f9662e6b0aa9 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -23,6 +23,7 @@
 import _imp
 import argparse
 import enum
+import json
 import logging
 import os
 import pathlib
@@ -118,8 +119,9 @@
 
 parser.add_argument(
     "--generate-stdlib-info",
-    action="store_true",
-    help="Generate file with stdlib module info",
+    nargs="?",
+    const=True,
+    help="Generate file with stdlib module info, with optional config file",
 )
 
 
@@ -287,7 +289,7 @@ def list_module_names(self, *, all: bool = False) -> set[str]:
             names.update(WINDOWS_MODULES)
         return names
 
-    def generate_stdlib_info(self) -> None:
+    def generate_stdlib_info(self, config_path: str | None = None) -> None:
 
         disabled_modules = {modinfo.name for modinfo in self.modules
                            if modinfo.state in (ModuleState.DISABLED, ModuleState.DISABLED_SETUP)}
@@ -296,6 +298,25 @@ def generate_stdlib_info(self) -> None:
         na_modules = {modinfo.name for modinfo in self.modules
                      if modinfo.state == ModuleState.NA}
 
+        config_messages = {}
+        if config_path:
+            try:
+                with open(config_path, encoding='utf-8') as f:
+                    config_messages = json.load(f)
+            except (FileNotFoundError, json.JSONDecodeError) as e:
+                logger.error("Failed to load distributor config %s: %s", config_path, e)
+
+        default_messages = {
+            **{name: f"Windows-only standard library module '{name}' was not found"
+               for name in WINDOWS_MODULES},
+            **{name: f"Standard library module disabled during build '{name}' was not found"
+               for name in disabled_modules},
+            **{name: f"Unsupported platform for standard library module '{name}'"
+               for name in na_modules},
+        }
+
+        messages = {**default_messages, **config_messages}
+
         content = f'''\
 # Standard library information used by the traceback module for more informative
 # ModuleNotFound error messages.
@@ -305,14 +326,7 @@ def generate_stdlib_info(self) -> None:
 NOT_AVAILABLE_MODULES = {sorted(na_modules)!r}
 WINDOWS_ONLY_MODULES = {sorted(WINDOWS_MODULES)!r}
 
-MISSING_STDLIB_MODULE_MESSAGES = {{
-    **{{name: f"Windows-only standard library module '{{name}}' was not found"
-        for name in WINDOWS_ONLY_MODULES}},
-    **{{name: f"Standard library module disabled during build '{{name}}' was not found"
-        for name in DISABLED_MODULES}},
-    **{{name: f"Unsupported platform for standard library module '{{name}}'"
-        for name in NOT_AVAILABLE_MODULES}},
-}}
+MISSING_STDLIB_MODULE_MESSAGES = {messages!r}
 '''
 
         output_path = self.builddir / "_stdlib_modules_info.py"
@@ -539,7 +553,8 @@ def main() -> None:
             print(name)
     elif args.generate_stdlib_info:
         checker.check()
-        checker.generate_stdlib_info()
+        config_path = None if args.generate_stdlib_info is True else args.generate_stdlib_info
+        checker.generate_stdlib_info(config_path)
     else:
         checker.check()
         checker.summary(verbose=args.verbose)
diff --git a/configure b/configure
index f95355e2f57d69..4d096cd55af4bc 100755
--- a/configure
+++ b/configure
@@ -1009,6 +1009,7 @@ UNIVERSALSDK
 host_exec_prefix
 host_prefix
 MACHDEP
+MISSING_STDLIB_CONFIG
 PKG_CONFIG_LIBDIR
 PKG_CONFIG_PATH
 PKG_CONFIG
@@ -1080,6 +1081,7 @@ ac_user_opts='
 enable_option_checking
 with_build_python
 with_pkg_config
+with_missing_stdlib_config
 enable_universalsdk
 with_universal_archs
 with_framework_name
@@ -1859,6 +1861,9 @@ Optional Packages:
   --with-pkg-config=[yes|no|check]
                           use pkg-config to detect build options (default is
                           check)
+  --with-missing-stdlib-config=FILE
+                          File with custom module error messages for missing
+                          stdlib modules
   --with-universal-archs=ARCH
                           specify the kind of macOS universal binary that
                           should be created. This option is only valid when
@@ -4092,6 +4097,19 @@ if test "$with_pkg_config" = yes -a -z "$PKG_CONFIG"; then
   as_fn_error $? "pkg-config is required" "$LINENO" 5]
 fi
 
+
+# Check whether --with-missing-stdlib-config was given.
+if test ${with_missing_stdlib_config+y}
+then :
+  withval=$with_missing_stdlib_config; MISSING_STDLIB_CONFIG="$withval"
+else case e in #(
+  e) MISSING_STDLIB_CONFIG=""
+ ;;
+esac
+fi
+
+
+
 # Set name for machine-dependent library files
 
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking MACHDEP" >&5
diff --git a/configure.ac b/configure.ac
index 4d0e5a1ca1d003..7540a2a77cc29b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -307,6 +307,15 @@ if test "$with_pkg_config" = yes -a -z "$PKG_CONFIG"; then
   AC_MSG_ERROR([pkg-config is required])]
 fi
 
+dnl Allow distributors to provide custom missing stdlib module error messages
+AC_ARG_WITH([missing-stdlib-config],
+  [AS_HELP_STRING([--with-missing-stdlib-config=FILE],
+                  [File with custom module error messages for missing stdlib modules])],
+  [MISSING_STDLIB_CONFIG="$withval"],
+  [MISSING_STDLIB_CONFIG=""]
+)
+AC_SUBST([MISSING_STDLIB_CONFIG])
+
 # Set name for machine-dependent library files
 AC_ARG_VAR([MACHDEP], [name for machine-dependent library files])
 AC_MSG_CHECKING([MACHDEP])

From 7a36850e934d250ea7f48f32595916fa69cdc028 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 30 Oct 2025 10:28:57 +0000
Subject: [PATCH 06/16] Docs & test

---
 Doc/using/configure.rst    | 21 +++++++++++++++++++++
 Doc/whatsnew/3.15.rst      |  6 ++++++
 Lib/test/test_traceback.py | 13 ++++++++++++-
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index 1f773a3a547c2b..22ec4effc6ecc6 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -255,6 +255,27 @@ General Options
 
    .. versionadded:: 3.11
 
+.. option:: --with-missing-stdlib-config=FILE
+
+   Path to a `JSON <https://www.json.org/json-en.html>`_ configuration file
+   containing custom error messages for missing :term:`standard library` modules.
+
+   This option is intended for Python distributors who wish to provide
+   distribution-specific guidance when users encounter missing standard library
+   modules that are packaged separately.
+
+   The JSON file should map missing module names to custom error message strings.
+   For example, a configuration for the :mod:`tkinter` module:
+
+   .. code-block::json
+
+      {
+          "tkinter": "Install the python-tk package to use tkinter",
+          "_tkinter": "Install the python-tk package to use tkinter"
+      }
+
+   .. versionadded:: next
+
 .. option:: --enable-pystats
 
    Turn on internal Python performance statistics gathering.
diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index 8503a4c7f973fc..5c51ef3da56e94 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/Doc/whatsnew/3.15.rst
@@ -229,6 +229,12 @@ Improved error messages
      AttributeError: 'Container' object has no attribute 'area'. Did you mean: 'inner.area'?
 
 
+* The new configure option :option:`--with-missing-stdlib-config=FILE` allows
+  distributors to pass a `JSON <https://www.json.org/json-en.html>`_
+  configuration file containing custom error messages for missing
+  :term:`standard library` modules.
+
+
 Other language changes
 ======================
 
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index bf57867a8715c0..97ae02489122f1 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5051,7 +5051,7 @@ def test_no_site_package_flavour(self):
              b"or to enable your virtual environment?"), stderr
         )
 
-    def test_missing_stdlib_package(self):
+    def test_missing_stdlib_module(self):
         code = """
             import sys
             sys.stdlib_module_names |= {'spam'}
@@ -5061,6 +5061,17 @@ def test_missing_stdlib_package(self):
 
         self.assertIn(b"Standard library module 'spam' was not found", stderr)
 
+        code = """
+            import sys
+            import traceback
+            traceback.MISSING_STDLIB_MODULE_MESSAGES = {'spam': 'Install 'spam4life' for 'spam''}
+            sys.stdlib_module_names |= {'spam'}
+            import spam
+        """
+        _, _, stderr = assert_python_failure('-S', '-c', code)
+
+        self.assertIn(b"Install 'spam4life' for 'spam'", stderr)
+
 
 class TestColorizedTraceback(unittest.TestCase):
     maxDiff = None

From 62ffb3998ce4beb1108b25f7724329b4a1ad64b3 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 30 Oct 2025 10:37:05 +0000
Subject: [PATCH 07/16] Blurb

---
 Doc/whatsnew/3.15.rst                                         | 1 +
 .../next/Build/2025-10-30-10-36-15.gh-issue-139707.QJ1FfJ.rst | 4 ++++
 2 files changed, 5 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Build/2025-10-30-10-36-15.gh-issue-139707.QJ1FfJ.rst

diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index 5c51ef3da56e94..4e2a7334a4378d 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/Doc/whatsnew/3.15.rst
@@ -233,6 +233,7 @@ Improved error messages
   distributors to pass a `JSON <https://www.json.org/json-en.html>`_
   configuration file containing custom error messages for missing
   :term:`standard library` modules.
+  (Contributed by Stan Ulbrych and Petr Viktorin in :gh:`139707`.)
 
 
 Other language changes
diff --git a/Misc/NEWS.d/next/Build/2025-10-30-10-36-15.gh-issue-139707.QJ1FfJ.rst b/Misc/NEWS.d/next/Build/2025-10-30-10-36-15.gh-issue-139707.QJ1FfJ.rst
new file mode 100644
index 00000000000000..d9870d267042af
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-10-30-10-36-15.gh-issue-139707.QJ1FfJ.rst
@@ -0,0 +1,4 @@
+Add configure option :option:`--with-missing-stdlib-config=FILE` allows
+which distributors to pass a `JSON <https://www.json.org/json-en.html>`_
+configuration file containing custom error messages for missing
+:term:`standard library` modules.

From 8d5ca012812c61c74c9984b227ba7dc30228dc98 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 30 Oct 2025 10:50:54 +0000
Subject: [PATCH 08/16] Fix test

---
 Lib/test/test_traceback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 97ae02489122f1..036e5d50d29442 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5064,7 +5064,7 @@ def test_missing_stdlib_module(self):
         code = """
             import sys
             import traceback
-            traceback.MISSING_STDLIB_MODULE_MESSAGES = {'spam': 'Install 'spam4life' for 'spam''}
+            traceback.MISSING_STDLIB_MODULE_MESSAGES = {'spam': "Install 'spam4life' for 'spam'"}
             sys.stdlib_module_names |= {'spam'}
             import spam
         """

From 185e890234450bc92aa531d5d9c12deaf7285536 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 30 Oct 2025 12:40:21 +0000
Subject: [PATCH 09/16] Fix example in doc

---
 Doc/using/configure.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index 22ec4effc6ecc6..a8d6ae0bf88bd1 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -267,11 +267,11 @@ General Options
    The JSON file should map missing module names to custom error message strings.
    For example, a configuration for the :mod:`tkinter` module:
 
-   .. code-block::json
+   .. code-block:: json
 
       {
           "tkinter": "Install the python-tk package to use tkinter",
-          "_tkinter": "Install the python-tk package to use tkinter"
+          "_tkinter": "Install the python-tk package to use tkinter",
       }
 
    .. versionadded:: next

From 902274cc1251a2c44443ebd3b09c6c54cef5bd8f Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Tue, 11 Nov 2025 17:49:36 +0000
Subject: [PATCH 10/16] Petr's review

---
 Doc/using/configure.rst                |  5 +++-
 Lib/test/test_traceback.py             | 10 ++++++++
 Lib/traceback.py                       |  4 ++--
 Tools/build/check_extension_modules.py | 32 ++++++++------------------
 4 files changed, 26 insertions(+), 25 deletions(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index a8d6ae0bf88bd1..18c5992518242f 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -265,11 +265,14 @@ General Options
    modules that are packaged separately.
 
    The JSON file should map missing module names to custom error message strings.
-   For example, a configuration for the :mod:`tkinter` module:
+   For example, if your distribution packages :mod:`tkinter` and
+   :mod:`_tkinter` separately and excludes :mod:`_gdbm` for legal reasons,
+   the configuration could contain:
 
    .. code-block:: json
 
       {
+          "_gdbm": "The '_gdbm' module is not available in this distribution"
           "tkinter": "Install the python-tk package to use tkinter",
           "_tkinter": "Install the python-tk package to use tkinter",
       }
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 036e5d50d29442..d6e4955b8011bb 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5072,6 +5072,16 @@ def test_missing_stdlib_module(self):
 
         self.assertIn(b"Install 'spam4life' for 'spam'", stderr)
 
+    @unittest.skipIf(sys.platform == "win32", "Non-Windows test")
+    def test_windows_only_module_error(self):
+        try:
+            import msvcrt  # noqa: F401
+        except ModuleNotFoundError:
+            formatted = traceback.format_exc()
+            self.assertIn("Unsupported platform for Windows-only standard library module 'msvcrt'", formatted)
+        else:
+            self.fail("ModuleNotFoundError was not raised")
+
 
 class TestColorizedTraceback(unittest.TestCase):
     maxDiff = None
diff --git a/Lib/traceback.py b/Lib/traceback.py
index b793449be3ae6e..02d6eb27c2b680 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1118,11 +1118,11 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
                 if MISSING_STDLIB_MODULE_MESSAGES is not None:
                     message = MISSING_STDLIB_MODULE_MESSAGES.get(
                         module_name,
-                        f"Standard library module '{module_name}' was not found"
+                        f"Standard library module {module_name!r} was not found"
                     )
                     self._str = message
                 else:
-                    self._str = f"Standard library module '{module_name}' was not found"
+                    self._str = f"Standard library module {module_name!r} was not found"
             elif sys.flags.no_site:
                 self._str += (". Site initialization is disabled, did you forget to "
                     + "add the site-packages directory to sys.path "
diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index f5f9662e6b0aa9..2c21fcf3703d12 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -290,14 +290,6 @@ def list_module_names(self, *, all: bool = False) -> set[str]:
         return names
 
     def generate_stdlib_info(self, config_path: str | None = None) -> None:
-
-        disabled_modules = {modinfo.name for modinfo in self.modules
-                           if modinfo.state in (ModuleState.DISABLED, ModuleState.DISABLED_SETUP)}
-        missing_modules = {modinfo.name for modinfo in self.modules
-                          if modinfo.state == ModuleState.MISSING}
-        na_modules = {modinfo.name for modinfo in self.modules
-                     if modinfo.state == ModuleState.NA}
-
         config_messages = {}
         if config_path:
             try:
@@ -306,26 +298,22 @@ def generate_stdlib_info(self, config_path: str | None = None) -> None:
             except (FileNotFoundError, json.JSONDecodeError) as e:
                 logger.error("Failed to load distributor config %s: %s", config_path, e)
 
-        default_messages = {
-            **{name: f"Windows-only standard library module '{name}' was not found"
-               for name in WINDOWS_MODULES},
-            **{name: f"Standard library module disabled during build '{name}' was not found"
-               for name in disabled_modules},
-            **{name: f"Unsupported platform for standard library module '{name}'"
-               for name in na_modules},
-        }
+        messages = {}
+        for name in WINDOWS_MODULES:
+            messages[name] = f"Unsupported platform for Windows-only standard library module {name!r}"
+
+        for modinfo in self.modules:
+            if modinfo.state in (ModuleState.DISABLED, ModuleState.DISABLED_SETUP):
+                messages[modinfo.name] = f"Standard library module disabled during build {modinfo.name!r} was not found"
+            elif modinfo.state == ModuleState.NA:
+                messages[modinfo.name] = f"Unsupported platform for standard library module {modinfo.name!r}"
 
-        messages = {**default_messages, **config_messages}
+        messages.update(config_messages)
 
         content = f'''\
 # Standard library information used by the traceback module for more informative
 # ModuleNotFound error messages.
 
-DISABLED_MODULES = {sorted(disabled_modules)!r}
-MISSING_MODULES = {sorted(missing_modules)!r}
-NOT_AVAILABLE_MODULES = {sorted(na_modules)!r}
-WINDOWS_ONLY_MODULES = {sorted(WINDOWS_MODULES)!r}
-
 MISSING_STDLIB_MODULE_MESSAGES = {messages!r}
 '''
 

From 9c74f697127214b324893e6e13af66aa23f13544 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Tue, 11 Nov 2025 18:11:45 +0000
Subject: [PATCH 11/16] Sphinx fix

---
 Doc/using/configure.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index 18c5992518242f..077047583292a2 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -266,7 +266,7 @@ General Options
 
    The JSON file should map missing module names to custom error message strings.
    For example, if your distribution packages :mod:`tkinter` and
-   :mod:`_tkinter` separately and excludes :mod:`_gdbm` for legal reasons,
+   :mod:`_tkinter` separately and excludes :mod:`!_gdbm` for legal reasons,
    the configuration could contain:
 
    .. code-block:: json

From 2ed0eb39696d3496bb12e493626845e9d70d3eaa Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 27 Nov 2025 15:21:40 +0000
Subject: [PATCH 12/16] Petr's review

---
 Doc/using/configure.rst                |  4 ++--
 Doc/whatsnew/3.15.rst                  | 13 ++++++------
 Lib/traceback.py                       | 15 ++++++--------
 Makefile.pre.in                        |  4 ++--
 Tools/build/check_extension_modules.py | 28 ++++++++++++++++----------
 5 files changed, 33 insertions(+), 31 deletions(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index 077047583292a2..c3bbb02f2cd71a 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -261,8 +261,8 @@ General Options
    containing custom error messages for missing :term:`standard library` modules.
 
    This option is intended for Python distributors who wish to provide
-   distribution-specific guidance when users encounter missing standard library
-   modules that are packaged separately.
+   distribution-specific guidance when users encounter standard library
+   modules that are missing or packaged separately.
 
    The JSON file should map missing module names to custom error message strings.
    For example, if your distribution packages :mod:`tkinter` and
diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index 4e2a7334a4378d..733914be09e4f4 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/Doc/whatsnew/3.15.rst
@@ -229,13 +229,6 @@ Improved error messages
      AttributeError: 'Container' object has no attribute 'area'. Did you mean: 'inner.area'?
 
 
-* The new configure option :option:`--with-missing-stdlib-config=FILE` allows
-  distributors to pass a `JSON <https://www.json.org/json-en.html>`_
-  configuration file containing custom error messages for missing
-  :term:`standard library` modules.
-  (Contributed by Stan Ulbrych and Petr Viktorin in :gh:`139707`.)
-
-
 Other language changes
 ======================
 
@@ -1062,6 +1055,12 @@ Build changes
   set to ``no`` or with :option:`!--without-system-libmpdec`.
   (Contributed by Sergey B Kirpichev in :gh:`115119`.)
 
+* The new configure option :option:`--with-missing-stdlib-config=FILE` allows
+  distributors to pass a `JSON <https://www.json.org/json-en.html>`_
+  configuration file containing custom error messages for :term:`standard library`
+  modules that are missing or packaged separately.
+  (Contributed by Stan Ulbrych and Petr Viktorin in :gh:`139707`.)
+
 
 Porting to Python 3.15
 ======================
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 02d6eb27c2b680..ffccaf89a78b44 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -17,7 +17,7 @@
 try:
     from _stdlib_modules_info import MISSING_STDLIB_MODULE_MESSAGES
 except ImportError:
-    MISSING_STDLIB_MODULE_MESSAGES = None
+    MISSING_STDLIB_MODULE_MESSAGES = {}
 
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
@@ -1115,14 +1115,11 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
         elif exc_type and issubclass(exc_type, ModuleNotFoundError):
             module_name = getattr(exc_value, "name", None)
             if module_name in sys.stdlib_module_names:
-                if MISSING_STDLIB_MODULE_MESSAGES is not None:
-                    message = MISSING_STDLIB_MODULE_MESSAGES.get(
-                        module_name,
-                        f"Standard library module {module_name!r} was not found"
-                    )
-                    self._str = message
-                else:
-                    self._str = f"Standard library module {module_name!r} was not found"
+                message = MISSING_STDLIB_MODULE_MESSAGES.get(
+                    module_name,
+                    f"Standard library module {module_name!r} was not found"
+                )
+                self._str = message
             elif sys.flags.no_site:
                 self._str += (". Site initialization is disabled, did you forget to "
                     + "add the site-packages directory to sys.path "
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 72c623a3d0ed52..a0fcc65e305c4b 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1602,9 +1602,9 @@ sharedmods: $(SHAREDMODS) pybuilddir.txt
 .PHONY: checksharedmods
 checksharedmods: sharedmods $(PYTHON_FOR_BUILD_DEPS) $(BUILDPYTHON)
 	@if [ -n "@MISSING_STDLIB_CONFIG@" ]; then \
-		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info="@MISSING_STDLIB_CONFIG@"; \
+		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-missing-stdlib-info --with-missing-stdlib-config="@MISSING_STDLIB_CONFIG@"; \
 	else \
-		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-stdlib-info; \
+		$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py --generate-missing-stdlib-info; \
 	fi
 	@$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/build/check_extension_modules.py
 
diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index 2c21fcf3703d12..edf850dcaf15d5 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -27,6 +27,7 @@
 import logging
 import os
 import pathlib
+import pprint
 import re
 import sys
 import sysconfig
@@ -118,10 +119,15 @@
 )
 
 parser.add_argument(
-    "--generate-stdlib-info",
-    nargs="?",
-    const=True,
-    help="Generate file with stdlib module info, with optional config file",
+    "--generate-missing-stdlib-info",
+    action="store_true",
+    help="Generate file with stdlib module info",
+)
+
+parser.add_argument(
+    "--with-missing-stdlib-config",
+    metavar="CONFIG_FILE",
+    help="Path to JSON config file with custom missing module messages",
 )
 
 
@@ -289,14 +295,14 @@ def list_module_names(self, *, all: bool = False) -> set[str]:
             names.update(WINDOWS_MODULES)
         return names
 
-    def generate_stdlib_info(self, config_path: str | None = None) -> None:
+    def generate_missing_stdlib_info(self, config_path: str | None = None) -> None:
         config_messages = {}
         if config_path:
             try:
                 with open(config_path, encoding='utf-8') as f:
                     config_messages = json.load(f)
             except (FileNotFoundError, json.JSONDecodeError) as e:
-                logger.error("Failed to load distributor config %s: %s", config_path, e)
+                raise RuntimeError("Failed to load missing stdlib config %s: %s", config_path, e)
 
         messages = {}
         for name in WINDOWS_MODULES:
@@ -313,11 +319,12 @@ def generate_stdlib_info(self, config_path: str | None = None) -> None:
         content = f'''\
 # Standard library information used by the traceback module for more informative
 # ModuleNotFound error messages.
+# Generated by check_extension_modules.py
 
-MISSING_STDLIB_MODULE_MESSAGES = {messages!r}
+MISSING_STDLIB_MODULE_MESSAGES = {pprint.pformat(messages)}
 '''
 
-        output_path = self.builddir / "_stdlib_modules_info.py"
+        output_path = self.builddir / "_missing_stdlib_module_info.py"
         with open(output_path, "w", encoding="utf-8") as f:
             f.write(content)
 
@@ -539,10 +546,9 @@ def main() -> None:
         names = checker.list_module_names(all=True)
         for name in sorted(names):
             print(name)
-    elif args.generate_stdlib_info:
+    elif args.generate_missing_stdlib_info:
         checker.check()
-        config_path = None if args.generate_stdlib_info is True else args.generate_stdlib_info
-        checker.generate_stdlib_info(config_path)
+        checker.generate_missing_stdlib_info(args.with_missing_stdlib_config)
     else:
         checker.check()
         checker.summary(verbose=args.verbose)

From f9b66b3603067f9aaff8ee599f1e98a30e84bfea Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 27 Nov 2025 15:23:25 +0000
Subject: [PATCH 13/16] Rename private module (again)

---
 Tools/build/check_extension_modules.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index edf850dcaf15d5..d37e51a0811087 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -324,7 +324,7 @@ def generate_missing_stdlib_info(self, config_path: str | None = None) -> None:
 MISSING_STDLIB_MODULE_MESSAGES = {pprint.pformat(messages)}
 '''
 
-        output_path = self.builddir / "_missing_stdlib_module_info.py"
+        output_path = self.builddir / "_missing_stdlib_info.py"
         with open(output_path, "w", encoding="utf-8") as f:
             f.write(content)
 

From 9ac50d9795f443b028f61d0a0e2392f98f4c2961 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 27 Nov 2025 15:57:01 +0000
Subject: [PATCH 14/16] Fix traceback.py import

---
 Lib/traceback.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/traceback.py b/Lib/traceback.py
index ffccaf89a78b44..791c430537d79d 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -15,7 +15,7 @@
 from contextlib import suppress
 
 try:
-    from _stdlib_modules_info import MISSING_STDLIB_MODULE_MESSAGES
+    from _missing_stdlib_info import MISSING_STDLIB_MODULE_MESSAGES
 except ImportError:
     MISSING_STDLIB_MODULE_MESSAGES = {}
 

From faea092d58b3eab7060dc79b018831dac3ec2999 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Thu, 27 Nov 2025 17:16:58 +0000
Subject: [PATCH 15/16] Fix install

---
 Makefile.pre.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile.pre.in b/Makefile.pre.in
index a0fcc65e305c4b..94aac003aa0e46 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -2820,7 +2820,7 @@ libinstall:	all $(srcdir)/Modules/xxmodule.c
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfigdata_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).py $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) `cat pybuilddir.txt`/_sysconfig_vars_$(ABIFLAGS)_$(MACHDEP)_$(MULTIARCH).json $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) `cat pybuilddir.txt`/build-details.json $(DESTDIR)$(LIBDEST); \
-	$(INSTALL_DATA) `cat pybuilddir.txt`/_stdlib_modules_info.py $(DESTDIR)$(LIBDEST); \
+	$(INSTALL_DATA) `cat pybuilddir.txt`/_missing_stdlib_info.py $(DESTDIR)$(LIBDEST); \
 	$(INSTALL_DATA) $(srcdir)/LICENSE $(DESTDIR)$(LIBDEST)/LICENSE.txt
 	@ # If app store compliance has been configured, apply the patch to the
 	@ # installed library code. The patch has been previously validated against

From 4c0c0bb49495dea551ad5bb75583482079f6e4e9 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@ulbrych.org>
Date: Fri, 28 Nov 2025 16:00:34 +0000
Subject: [PATCH 16/16] Petr's notes

---
 Lib/test/test_traceback.py             | 2 +-
 Lib/traceback.py                       | 6 +++---
 Tools/build/check_extension_modules.py | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index d6e4955b8011bb..3876f1a74bbc1a 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5064,7 +5064,7 @@ def test_missing_stdlib_module(self):
         code = """
             import sys
             import traceback
-            traceback.MISSING_STDLIB_MODULE_MESSAGES = {'spam': "Install 'spam4life' for 'spam'"}
+            traceback._MISSING_STDLIB_MODULE_MESSAGES = {'spam': "Install 'spam4life' for 'spam'"}
             sys.stdlib_module_names |= {'spam'}
             import spam
         """
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 791c430537d79d..8a3e0f77e765dc 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -15,9 +15,9 @@
 from contextlib import suppress
 
 try:
-    from _missing_stdlib_info import MISSING_STDLIB_MODULE_MESSAGES
+    from _missing_stdlib_info import _MISSING_STDLIB_MODULE_MESSAGES
 except ImportError:
-    MISSING_STDLIB_MODULE_MESSAGES = {}
+    _MISSING_STDLIB_MODULE_MESSAGES = {}
 
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
@@ -1115,7 +1115,7 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
         elif exc_type and issubclass(exc_type, ModuleNotFoundError):
             module_name = getattr(exc_value, "name", None)
             if module_name in sys.stdlib_module_names:
-                message = MISSING_STDLIB_MODULE_MESSAGES.get(
+                message = _MISSING_STDLIB_MODULE_MESSAGES.get(
                     module_name,
                     f"Standard library module {module_name!r} was not found"
                 )
diff --git a/Tools/build/check_extension_modules.py b/Tools/build/check_extension_modules.py
index d37e51a0811087..f23c1d5286f92a 100644
--- a/Tools/build/check_extension_modules.py
+++ b/Tools/build/check_extension_modules.py
@@ -302,7 +302,7 @@ def generate_missing_stdlib_info(self, config_path: str | None = None) -> None:
                 with open(config_path, encoding='utf-8') as f:
                     config_messages = json.load(f)
             except (FileNotFoundError, json.JSONDecodeError) as e:
-                raise RuntimeError("Failed to load missing stdlib config %s: %s", config_path, e)
+                raise RuntimeError(f"Failed to load missing stdlib config {config_path!r}") from e
 
         messages = {}
         for name in WINDOWS_MODULES:
@@ -321,7 +321,7 @@ def generate_missing_stdlib_info(self, config_path: str | None = None) -> None:
 # ModuleNotFound error messages.
 # Generated by check_extension_modules.py
 
-MISSING_STDLIB_MODULE_MESSAGES = {pprint.pformat(messages)}
+_MISSING_STDLIB_MODULE_MESSAGES = {pprint.pformat(messages)}
 '''
 
         output_path = self.builddir / "_missing_stdlib_info.py"