bpo-28468: Add platform.freedesktop_os_release() (GH-23492)

Add platform.freedesktop_os_release() function to parse freedesktop.org
os-release files.

Signed-off-by: Christian Heimes <christian@python.org>
Co-authored-by: Victor Stinner <vstinner@python.org>

Lib/platform.py

@@ -1230,6 +1230,63 @@ def platform(aliased=0, terse=0):
     _platform_cache[(aliased, terse)] = platform
     return platform
 
+### freedesktop.org os-release standard
+# https://www.freedesktop.org/software/systemd/man/os-release.html
+
+# NAME=value with optional quotes (' or "). The regular expression is less
+# strict than shell lexer, but that's ok.
+_os_release_line = re.compile(
+    "^(?P<name>[a-zA-Z0-9_]+)=(?P<quote>[\"\']?)(?P<value>.*)(?P=quote)$"
+)
+# unescape five special characters mentioned in the standard
+_os_release_unescape = re.compile(r"\\([\\\$\"\'`])")
+# /etc takes precedence over /usr/lib
+_os_release_candidates = ("/etc/os-release", "/usr/lib/os-relesase")
+_os_release_cache = None
+
+
+def _parse_os_release(lines):
+    # These fields are mandatory fields with well-known defaults
+    # in pratice all Linux distributions override NAME, ID, and PRETTY_NAME.
+    info = {
+        "NAME": "Linux",
+        "ID": "linux",
+        "PRETTY_NAME": "Linux",
+    }
+
+    for line in lines:
+        mo = _os_release_line.match(line)
+        if mo is not None:
+            info[mo.group('name')] = _os_release_unescape.sub(
+                r"\1", mo.group('value')
+            )
+
+    return info
+
+
+def freedesktop_os_release():
+    """Return operation system identification from freedesktop.org os-release
+    """
+    global _os_release_cache
+
+    if _os_release_cache is None:
+        errno = None
+        for candidate in _os_release_candidates:
+            try:
+                with open(candidate, encoding="utf-8") as f:
+                    _os_release_cache = _parse_os_release(f)
+                break
+            except OSError as e:
+                errno = e.errno
+        else:
+            raise OSError(
+                errno,
+                f"Unable to read files {', '.join(_os_release_candidates)}"
+            )
+
+    return _os_release_cache.copy()
+
+
 ### Command line interface
 
 if __name__ == '__main__':