tools/docs: python_version: move version check from sphinx-pre-install

The sphinx-pre-install code has some logic to deal with Python
version, which ensures that a minimal version will be enforced
for documentation build logic.

Move it to a separate library to allow re-using its code.

No functional changes.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <d134ace64b55c827565ce68f0527e20c735f0d2e.1758196090.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

tools/docs/lib/python_version.py

@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2017-2025 Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+
+"""
+Handle Python version check logic.
+
+Not all Python versions are supported by scripts. Yet, on some cases,
+like during documentation build, a newer version of python could be
+available.
+
+This class allows checking if the minimal requirements are followed.
+
+Better than that, PythonVersion.check_python() not only checks the minimal
+requirements, but it automatically switches to a the newest available
+Python version if present.
+
+"""
+
+import os
+import re
+import subprocess
+import sys
+
+from glob import glob
+
+class PythonVersion:
+    """
+    Ancillary methods that checks for missing dependencies for different
+    types of types, like binaries, python modules, rpm deps, etc.
+    """
+
+    def __init__(self, version):
+        """Ïnitialize self.version tuple from a version string"""
+        self.version = self.parse_version(version)
+
+    @staticmethod
+    def parse_version(version):
+        """Convert a major.minor.patch version into a tuple"""
+        return tuple(int(x) for x in version.split("."))
+
+    @staticmethod
+    def ver_str(version):
+        """Returns a version tuple as major.minor.patch"""
+        return ".".join([str(x) for x in version])
+
+    def __str__(self):
+        """Returns a version tuple as major.minor.patch from self.version"""
+        return self.ver_str(self.version)
+
+    @staticmethod
+    def get_python_version(cmd):
+        """
+        Get python version from a Python binary. As we need to detect if
+        are out there newer python binaries, we can't rely on sys.release here.
+        """
+
+        kwargs = {}
+        if sys.version_info < (3, 7):
+            kwargs['universal_newlines'] = True
+        else:
+            kwargs['text'] = True
+
+        result = subprocess.run([cmd, "--version"],
+                                stdout = subprocess.PIPE,
+                                stderr = subprocess.PIPE,
+                                **kwargs, check=False)
+
+        version = result.stdout.strip()
+
+        match = re.search(r"(\d+\.\d+\.\d+)", version)
+        if match:
+            return PythonVersion.parse_version(match.group(1))
+
+        print(f"Can't parse version {version}")
+        return (0, 0, 0)
+
+    @staticmethod
+    def find_python(min_version):
+        """
+        Detect if are out there any python 3.xy version newer than the
+        current one.
+
+        Note: this routine is limited to up to 2 digits for python3. We
+        may need to update it one day, hopefully on a distant future.
+        """
+        patterns = [
+            "python3.[0-9][0-9]",
+            "python3.[0-9]",
+        ]
+
+        python_cmd = []
+
+        # Seek for a python binary newer than min_version
+        for path in os.getenv("PATH", "").split(":"):
+            for pattern in patterns:
+                for cmd in glob(os.path.join(path, pattern)):
+                    if os.path.isfile(cmd) and os.access(cmd, os.X_OK):
+                        version = PythonVersion.get_python_version(cmd)
+                        if version >= min_version:
+                            python_cmd.append((version, cmd))
+
+        return sorted(python_cmd, reverse=True)
+
+    @staticmethod
+    def check_python(min_version, show_alternatives=False, bail_out=False,
+                     success_on_error=False):
+        """
+        Check if the current python binary satisfies our minimal requirement
+        for Sphinx build. If not, re-run with a newer version if found.
+        """
+        cur_ver = sys.version_info[:3]
+        if cur_ver >= min_version:
+            ver = PythonVersion.ver_str(cur_ver)
+            return
+
+        python_ver = PythonVersion.ver_str(cur_ver)
+
+        available_versions = PythonVersion.find_python(min_version)
+        if not available_versions:
+            print(f"ERROR: Python version {python_ver} is not spported anymore\n")
+            print("       Can't find a new version. This script may fail")
+            return
+
+        script_path = os.path.abspath(sys.argv[0])
+
+        # Check possible alternatives
+        if available_versions:
+            new_python_cmd = available_versions[0][1]
+        else:
+            new_python_cmd = None
+
+        if show_alternatives:
+            print("You could run, instead:")
+            for _, cmd in available_versions:
+                args = [cmd, script_path] + sys.argv[1:]
+
+                cmd_str = " ".join(args)
+                print(f"  {cmd_str}")
+            print()
+
+        if bail_out:
+            msg = f"Python {python_ver} not supported. Bailing out"
+            if success_on_error:
+                print(msg, file=sys.stderr)
+                sys.exit(0)
+            else:
+                sys.exit(msg)
+
+        print(f"Python {python_ver} not supported. Changing to {new_python_cmd}")
+
+        # Restart script using the newer version
+        args = [new_python_cmd, script_path] + sys.argv[1:]
+
+        try:
+            os.execv(new_python_cmd, args)
+        except OSError as e:
+            sys.exit(f"Failed to restart with {new_python_cmd}: {e}")