Raise an exception on unsupported Python versions

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/), and this project
 adheres to [Semantic Versioning](https://semver.org/).
 
+## Unreleased
+
+### :bug: Fixes
+
+- Raise an exception at both build and runtime when using an unsupported Python version,
+  instead of crashing with a segmentation fault at runtime (in the rare cases where
+  `backports.zstd` was installed despite the `requires-python` marker)
+
 ## [1.2.0] - 2025-12-06
 
 [1.2.0]: https://github.com/rogdham/backports.zstd/releases/tag/v1.2.0

setup.py

@@ -6,6 +6,10 @@
 
 from setuptools import Extension, setup
 
+if not ((3, 9) <= sys.version_info < (3, 14)):
+    raise RuntimeError(f"Unsupported Python version: {sys.version}")
+
+
 # create a LICENSE_zstd.txt file
 # wheels distributions needs to ship the license of the zstd library
 ROOT_PATH = Path(__file__).parent.absolute()

src/python/backports/zstd/__init__.py

@@ -1,5 +1,9 @@
 """Python bindings to the Zstandard (zstd) compression library (RFC-8878)."""
 
+import sys
+if not ((3, 9) <= sys.version_info < (3, 14)):
+    raise RuntimeError(f"Unsupported Python version: {sys.version}")
+
 __all__ = (
     # backports.zstd
     'COMPRESSION_LEVEL_DEFAULT',