From 4ad84cb8294cacb6c430d61bdd40137ffcd0c6f7 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Fri, 21 Aug 2026 19:30:38 +0100
Subject: [PATCH] Refuse to run `make doctest` under a mismatched Python

---
 Doc/Makefile |  8 ++++++++
 Doc/make.bat | 13 +++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/Doc/Makefile b/Doc/Makefile
index d77ece1e681bcf..6674534f194035 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -132,6 +132,14 @@ coverage: build
 .PHONY: doctest
 doctest: BUILDER = doctest
 doctest:
+	@venv_version=$$($(VENVDIR)/bin/python3 -c 'import sys; print("%d.%d" % sys.version_info[:2])'); \
+	tree_version=$$($(PYTHON) tools/extensions/patchlevel.py --short); \
+	if [ "$$venv_version" != "$$tree_version" ]; then \
+		echo "The venv runs Python $$venv_version, but this source tree is Python $$tree_version."; \
+		echo "The doctests are executed by the venv interpreter, so they would test"; \
+		echo "Python $$venv_version rather than the code documented here."; \
+		exit 1; \
+	fi
 	@$(MAKE) build BUILDER=$(BUILDER) || { \
 	echo "Testing of doctests in the sources finished, look at the" \
 	     "results in build/doctest/output.txt"; \
diff --git a/Doc/make.bat b/Doc/make.bat
index 99f0d5c44f0098..132b21c5b2fce8 100644
--- a/Doc/make.bat
+++ b/Doc/make.bat
@@ -9,6 +9,19 @@ call ..\PCbuild\find_python.bat %PYTHON%
 
 if not defined PYTHON set PYTHON=py
 
+if "%1" NEQ "doctest" goto :skipversioncheck
+for /f "usebackq" %%v in (`%PYTHON% -c "import sys; print(sys.version_info[0], sys.version_info[1], sep='.')"`) do set PYVERSION=%%v
+for /f "usebackq" %%v in (`%PYTHON% tools/extensions/patchlevel.py --short`) do set TREEVERSION=%%v
+if "%PYVERSION%" NEQ "%TREEVERSION%" (
+    echo.
+    echo.%PYTHON% is Python %PYVERSION%, but this source tree is Python %TREEVERSION%.
+    echo.The doctests are executed by that interpreter, so they would test
+    echo.Python %PYVERSION% rather than the code documented here.
+    popd
+    exit /B 1
+)
+:skipversioncheck
+
 if not defined SPHINXBUILD (
     %PYTHON% -c "import sphinx" > nul 2> nul
     if errorlevel 1 (