Check python version in __pip-runner__.py

Author: pfmoore

setup.py

@@ -81,5 +81,7 @@ def get_version(rel_path: str) -> str:
         ],
     },
     zip_safe=False,
+    # NOTE: python_requires is duplicated in __pip-runner__.py.
+    # When changing this value, please change the other copy as well.
     python_requires=">=3.7",
 )

src/pip/__pip-runner__.py

@@ -12,6 +12,8 @@
 from typing import Optional, Sequence, Union
 
 PIP_SOURCES_ROOT = dirname(dirname(__file__))
+# Copied from setup.py
+PYTHON_REQUIRES = ">=3.7"
 
 
 class PipImportRedirectingFinder:
@@ -30,8 +32,22 @@ def find_spec(
         return spec
 
 
+def check_python_version():
+    # Import here to ensure the imports happen after the sys.meta_path change.
+    from pip._vendor.packaging.version import Version
+    from pip._vendor.packaging.specifiers import SpecifierSet
+
+    py_ver = Version("{0.major}.{0.minor}.{0.micro}".format(sys.version_info))
+    if py_ver not in SpecifierSet(PYTHON_REQUIRES):
+        raise SystemExit(
+            f"This version of pip does not support python {py_ver} "
+            f"(requires {PYTHON_REQUIRES})"
+        )
+
+
 # TODO https://github.com/pypa/pip/issues/11294
 sys.meta_path.insert(0, PipImportRedirectingFinder())
 
 assert __name__ == "__main__", "Cannot run __pip-runner__.py as a non-main module"
+check_python_version()
 runpy.run_module("pip", run_name="__main__", alter_sys=True)