Elep

"""Implement https://www.python.org/dev/peps/pep-0514/ to discover interpreters - Windows only"""

import os
import re
import winreg
from logging import basicConfig, getLogger

LOGGER = getLogger(__name__)

def enum_keys(key):
    at = 0
    while True:
        try:
            yield winreg.EnumKey(key, at)
        except OSError:
            break
        at += 1

def get_value(key, value_name):
    try:
        return winreg.QueryValueEx(key, value_name)[0]
    except OSError:
        return None

def discover_pythons():
    for hive, hive_name, key, flags, default_arch in [
        (winreg.HKEY_CURRENT_USER, "HKEY_CURRENT_USER", r"Software\Python", 0, 64),
        (winreg.HKEY_LOCAL_MACHINE, "HKEY_LOCAL_MACHINE", r"Software\Python", winreg.KEY_WOW64_64KEY, 64),
        (winreg.HKEY_LOCAL_MACHINE, "HKEY_LOCAL_MACHINE", r"Software\Python", winreg.KEY_WOW64_32KEY, 32),
    ]:
        yield from process_set(hive, hive_name, key, flags, default_arch)

def process_set(hive, hive_name, key, flags, default_arch):
    try:
        with winreg.OpenKeyEx(hive, key, 0, winreg.KEY_READ | flags) as root_key:
            for company in enum_keys(root_key):
                if company == "PyLauncher":  # reserved
                    continue
                yield from process_company(hive_name, company, root_key, default_arch)
    except OSError:
        pass

def process_company(hive_name, company, root_key, default_arch):
    with winreg.OpenKeyEx(root_key, company) as company_key:
        for tag in enum_keys(company_key):
            spec = process_tag(hive_name, company, company_key, tag, default_arch)
            if spec is not None:
                yield spec

def process_tag(hive_name, company, company_key, tag, default_arch):
    with winreg.OpenKeyEx(company_key, tag) as tag_key:
        version = load_version_data(hive_name, company, tag, tag_key)
        if version is not None:  # if failed to get version bail
            major, minor, _ = version
            arch = load_arch_data(hive_name, company, tag, tag_key, default_arch)
            if arch is not None:
                exe_data = load_exe(hive_name, company, company_key, tag)
                if exe_data is not None:
                    exe, args = exe_data
                    return company, major, minor, arch, exe, args

def load_exe(hive_name, company, company_key, tag):
    key_path = f"{hive_name}/{company}/{tag}"
    try:
        with winreg.OpenKeyEx(company_key, rf"{tag}\InstallPath") as ip_key:
            with ip_key:
                exe = get_value(ip_key, "ExecutablePath")
                if exe is None:
                    ip = get_value(ip_key, None)
                    if ip is None:
                        msg(key_path, "no ExecutablePath or default for it")

else:
                        exe = os.path.join(ip, "python.exe")
                if exe is not None and os.path.exists(exe):
                    args = get_value(ip_key, "ExecutableArguments")
                    return exe, args
                else:
                    msg(key_path, f"could not load exe with value {exe}")
    except OSError:
        msg(f"{key_path}/InstallPath", "missing")
    return None

def load_arch_data(hive_name, company, tag, tag_key, default_arch):
    arch_str = get_value(tag_key, "SysArchitecture")
    if arch_str is not None:
        key_path = f"{hive_name}/{company}/{tag}/SysArchitecture"
        try:
            return parse_arch(arch_str)
        except ValueError as sys_arch:
            msg(key_path, sys_arch)
    return default_arch

def parse_arch(arch_str):
    if isinstance(arch_str, str):
        match = re.match(r"^(\d+)bit$", arch_str)
        if match:
            return int(next(iter(match.groups())))
        error = f"invalid format {arch_str}"
    else:
        error = f"arch is not string: {repr(arch_str)}"
    raise ValueError(error)

def load_version_data(hive_name, company, tag, tag_key):
    for candidate, key_path in [
        (get_value(tag_key, "SysVersion"), f"{hive_name}/{company}/{tag}/SysVersion"),
        (tag, f"{hive_name}/{company}/{tag}"),
    ]:
        if candidate is not None:
            try:
                return parse_version(candidate)
            except ValueError as sys_version:
                msg(key_path, sys_version)
    return None

def parse_version(version_str):
    if isinstance(version_str, str):
        match = re.match(r"^(\d+)(?:\.(\d+))?(?:\.(\d+))?$", version_str)
        if match:
            return tuple(int(i) if i is not None else None for i in match.groups())
        error = f"invalid format {version_str}"
    else:
        error = f"version is not string: {version_str!r}"
    raise ValueError(error)

def msg(path, what):
    LOGGER.warning(f"PEP-514 violation in Windows Registry at {path} error: {what}")

def _run():
    basicConfig()
    interpreters = []
    for spec in discover_pythons():
        interpreters.append(repr(spec))
    print("\n".join(sorted(interpreters)))

if __name__ == "__main__":
    _run()