Sync pre-release CPython main branch from GitHub (2026-07-21)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`20b7e8e`](https://www.github.com/python/cpython/commit/20b7e8e50b9a4a92989b36531429f9b51ee0a0bf) (committed 2026-07-21 00:46:48+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`f62050d`](https://www.github.com/python/cpython/commit/f62050d65743f0c895f7e6d665936c4e86aa39d5) (commit date: 2026-07-16 17:37:00+00:00)
- Imported: (`3.16.0a0`) - [`20b7e8e`](https://www.github.com/python/cpython/commit/20b7e8e50b9a4a92989b36531429f9b51ee0a0bf) (commit date: 2026-07-21 00:46:48+00:00)

# Noteworthy file changes

- Build system files (6 removed): `PCbuild/pylauncher.vcxproj`, `PCbuild/pylauncher.vcxproj.filters`, `PCbuild/pyshellext.vcxproj`, `PCbuild/pyshellext.vcxproj.filters`, `PCbuild/pywlauncher.vcxproj`, `PCbuild/pywlauncher.vcxproj.filters`
- Native files (4 removed):
  ```
  - PC/launcher.c
  - PC/launcher2.c
  - Tools/msi/bundle/bootstrap/pch.h
  - Tools/msi/bundle/bootstrap/resource.h
  ```
- Test files (4 added, 1 removed)
- Low-signal files (49 added, 4 removed) (NEWS.d, docs, .github)
- Other files (4 added, 154 removed)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GPIc7xxq-Cw_k_AEAMAutom6PPo-br0LAAAz

Reviewed By: DinoV

Differential Revision: D112963960

fbshipit-source-id: 1a525fae9ef28cf47d397f24d7ddc9961b34b6d7

Author: itamaro

.azure-pipelines/windows-layout-steps.yml

@@ -12,7 +12,7 @@ steps:
   displayName: Show layout info (${{ parameters.kind }})
 
 - ${{ if eq(parameters.fulltest, 'true') }}:
-  - script: .\python.exe -m test -q -uall -u-cpu -rwW --slowest --timeout=1200 -j0 --junit-xml="$(Build.BinariesDirectory)\test-results-${{ parameters.kind }}.xml" --tempdir "$(Build.BinariesDirectory)\tmp-${{ parameters.kind }}-$(arch)" -i test_launcher
+  - script: .\python.exe -m test -q -uall -u-cpu -rwW --slowest --timeout=1200 -j0 --junit-xml="$(Build.BinariesDirectory)\test-results-${{ parameters.kind }}.xml" --tempdir "$(Build.BinariesDirectory)\tmp-${{ parameters.kind }}-$(arch)"
     workingDirectory: $(Build.BinariesDirectory)\layout-${{ parameters.kind }}-$(arch)
     displayName: ${{ parameters.kind }} Tests
     env:

.gitattributes

@@ -19,7 +19,7 @@
 *.zip binary
 
 # Specific binary files
-PC/classicAppCompat.* binary
+# -- None right now --
 
 # Text files that should not be subject to eol conversion
 [attr]noeol -text

.github/CODEOWNERS

@@ -188,12 +188,8 @@ Tools/wasm/wasi               @brettcannon @emmatyping @savannahostrowski
 PC/                           @python/windows-team
 PCbuild/                      @python/windows-team
 
-# Windows installer packages
-Tools/msi/                    @python/windows-team
-Tools/nuget/                  @python/windows-team
-
-# Windows Launcher
-PC/launcher.c                 @python/windows-team @vsajip
+# Windows Venv launcher/redirector
+PC/venvlauncher.c             @python/windows-team @vsajip
 
 
 # ----------------------------------------------------------------------------

.github/workflows/build.yml

@@ -181,22 +181,6 @@ jobs:
       free-threading: ${{ matrix.free-threading }}
       interpreter: ${{ matrix.interpreter }}
 
-  build-windows-msi:
-    # ${{ '' } is a hack to nest jobs under the same sidebar category.
-    name: Windows MSI${{ '' }}  # zizmor: ignore[obfuscation]
-    needs: build-context
-    if: fromJSON(needs.build-context.outputs.run-windows-msi)
-    strategy:
-      fail-fast: false
-      matrix:
-        arch:
-        - x86
-        - x64
-        - arm64
-    uses: ./.github/workflows/reusable-windows-msi.yml
-    with:
-      arch: ${{ matrix.arch }}
-
   build-macos:
     name: >-
       macOS
@@ -650,7 +634,6 @@ jobs:
     - check-generated-files
     - check-c-api-docs
     - build-windows
-    - build-windows-msi
     - build-macos
     - build-ubuntu
     - build-ubuntu-ssltests
@@ -671,7 +654,6 @@ jobs:
         allowed-failures: >-
           build-android,
           build-emscripten,
-          build-windows-msi,
           build-ubuntu-ssltests,
           test-hypothesis,
           cifuzz,

.github/workflows/reusable-context.yml

@@ -47,9 +47,6 @@ on:  # yamllint disable-line rule:truthy
       run-wasi:
         description: Whether to run the WASI tests
         value: ${{ jobs.compute-changes.outputs.run-wasi }}  # bool
-      run-windows-msi:
-        description: Whether to run the MSI installer smoke tests
-        value: ${{ jobs.compute-changes.outputs.run-windows-msi }}  # bool
       run-windows-tests:
         description: Whether to run the Windows tests
         value: ${{ jobs.compute-changes.outputs.run-windows-tests }}  # bool
@@ -73,7 +70,6 @@ jobs:
       run-ubuntu: ${{ steps.changes.outputs.run-ubuntu }}
       run-emscripten: ${{ steps.changes.outputs.run-emscripten }}
       run-wasi: ${{ steps.changes.outputs.run-wasi }}
-      run-windows-msi: ${{ steps.changes.outputs.run-windows-msi }}
       run-windows-tests: ${{ steps.changes.outputs.run-windows-tests }}
     steps:
     - name: Set up Python

.github/workflows/reusable-san.yml

@@ -39,6 +39,8 @@ jobs:
       run: |
         sudo ./.github/workflows/posix-deps-apt.sh
         # On ubuntu-26.04 image, clang is clang-21 by default
+        # NOTE: when bumping to a new version of clang,
+        # please update the versions in `Tools/pixi-packages/variants.yaml` too.
         echo "CC=clang" >> "$GITHUB_ENV"
         echo "CXX=clang++" >> "$GITHUB_ENV"
     - name: TSan option setup

.github/workflows/reusable-windows-msi.yml

@@ -50,7 +50,7 @@ gmon.out
 
 *.exe
 
-# Ignore core dumps... but not Tools/msi/core/ or the like.
+# Ignore core dumps... but not .../core/ subdirectories
 core
 !core/
 
@@ -158,7 +158,6 @@ Tools/unicode/data/
 /coverage/
 /externals/
 /htmlcov/
-Tools/msi/obj
 Tools/ssl/amd64
 Tools/ssl/win32
 Tools/freeze/test/outdir

.gitignore

@@ -499,12 +499,12 @@ Querying the error indicator
 .. c:function:: void PyErr_SetRaisedException(PyObject *exc)
 
    Set *exc* as the exception currently being raised,
-   clearing the existing exception if one is set.
+   clearing the existing exception if one is set.  If *exc* is ``NULL``,
+   just clear the existing exception.
 
-   .. warning::
+   *exc* must be a valid exception or ``NULL``.
 
-      This call ":term:`steals <steal>`" a reference to *exc*,
-      which must be a valid exception.
+   This call ":term:`steals <steal>`" a reference to *exc*.
 
    .. versionadded:: 3.12
 

Doc/c-api/exceptions.rst

@@ -243,3 +243,62 @@ Unless using :pep:`523`, you will not need this.
    Return the currently executing line number, or -1 if there is no line number.
 
    .. versionadded:: 3.12
+
+
+.. c:var:: const PyTypeObject *PyUnstable_ExecutableKinds
+
+   An array of executable kinds (executor types) for frames, used for internal
+   debugging and tracing.
+
+   Tools like debuggers and profilers can use this to identify the type of execution
+   context associated with a frame (such as to filter out internal frames).
+   The entries are indexed by the following constants:
+
+   .. list-table::
+      :header-rows: 1
+      :widths: auto
+
+      * - Constant
+        - Description
+      * - .. c:macro:: PyUnstable_EXECUTABLE_KIND_SKIP
+        - The frame is internal (For example: inlined) and should be skipped by tools.
+      * - .. c:macro:: PyUnstable_EXECUTABLE_KIND_PY_FUNCTION
+        - The frame corresponds to a standard Python function.
+      * - .. c:macro:: PyUnstable_EXECUTABLE_KIND_BUILTIN_FUNCTION
+        - The frame corresponds to a function defined in native code.
+      * - .. c:macro:: PyUnstable_EXECUTABLE_KIND_METHOD_DESCRIPTOR
+        - The frame corresponds to a method on a class instance.
+
+   However, Python's C API lacks a function to read the executable kind from
+   a frame. Instead, use this recipe:
+
+   .. code-block:: c
+
+      int
+      get_executable_kind(PyFrameObject *frame)
+      {
+         _PyInterpreterFrame *f = frame->f_frame;
+         PyObject *exec = PyStackRef_AsPyObjectBorrow(f->f_executable);
+
+         if (PyCode_Check(exec)) {
+            return PyUnstable_EXECUTABLE_KIND_PY_FUNCTION;
+         }
+         if (PyMethod_Check(exec)) {
+            return PyUnstable_EXECUTABLE_KIND_BUILTIN_FUNCTION;
+         }
+         if (Py_IS_TYPE(exec, &PyMethodDescr_Type)) {
+            return PyUnstable_EXECUTABLE_KIND_METHOD_DESCRIPTOR;
+         }
+
+         return PyUnstable_EXECUTABLE_KIND_SKIP;
+      }
+
+   .. versionadded:: 3.13
+
+
+.. c:macro:: PyUnstable_EXECUTABLE_KINDS
+
+   The number of entries in :c:data:`PyUnstable_ExecutableKinds`.
+
+   .. versionadded:: 3.13
+