HKEY_CURRENT_USER\Software\Python\<Company>\<Tag>
HKEY_LOCAL_MACHINE\Software\Python\<Company>\<Tag>
HKEY_LOCAL_MACHINE\Software\Wow6432Node\Python\<Company>\<Tag>

# Display most-preferred environments.
# Assumes a 64-bit operating system
# Does not correctly handle PythonCore compatibility

import winreg

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

def get_value(key, value_name):
    try:
        return winreg.QueryValue(key, value_name)
    except FileNotFoundError:
        return None

seen = set()
for hive, key, flags in [
    (winreg.HKEY_CURRENT_USER, r'Software\Python', 0),
    (winreg.HKEY_LOCAL_MACHINE, r'Software\Python', winreg.KEY_WOW64_64KEY),
    (winreg.HKEY_LOCAL_MACHINE, r'Software\Python', winreg.KEY_WOW64_32KEY),
]:
    with winreg.OpenKeyEx(hive, key, access=winreg.KEY_READ | flags) as root_key:
        for company in enum_keys(root_key):
            if company == 'PyLauncher':
                continue

            with winreg.OpenKey(root_key, company) as company_key:
                for tag in enum_keys(company_key):
                    if (company, tag) in seen:
                        if company == 'PythonCore':
                            # TODO: Backwards compatibility handling
                            pass
                        continue
                    seen.add((company, tag))

                    try:
                        with winreg.OpenKey(company_key, tag + r'\InstallPath') as ip_key:
                            exec_path = get_value(ip_key, 'ExecutablePath')
                            exec_args = get_value(ip_key, 'ExecutableArguments')
                            if company == 'PythonCore' and not exec_path:
                                # TODO: Backwards compatibility handling
                                pass
                    except OSError:
                        exec_path, exec_args = None, None

                    if exec_path:
                        print('{}\\{} - {} {}'.format(company, tag, exec_path, exec_args or ''))
                    else:
                        print('{}\\{} - (not executable)'.format(company, tag))

# Only lists per-user PythonCore registrations
# Uses fallback values as described in PEP 514

import os
import winreg

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

def get_value(key, value_name):
    try:
        return winreg.QueryValue(key, value_name)
    except FileNotFoundError:
        return None

with winreg.OpenKey(winreg.HKEY_CURRENT_USER, r"Software\Python\PythonCore") as company_key:
    print('Company:', get_value(company_key, 'DisplayName') or 'Python Software Foundation')
    print('Support:', get_value(company_key, 'SupportUrl') or 'https://pythonlang.cn/')
    print()

    for tag in enum_keys(company_key):
        with winreg.OpenKey(company_key, tag) as tag_key:
            print('PythonCore\\' + tag)
            print('Name:', get_value(tag_key, 'DisplayName') or ('Python ' + tag))
            print('Support:', get_value(tag_key, 'SupportUrl') or 'https://pythonlang.cn/')
            print('Version:', get_value(tag_key, 'Version') or tag[:3])
            print('SysVersion:', get_value(tag_key, 'SysVersion') or tag[:3])
            # Architecture is unknown because we are in HKCU
            # Tools may use alternate approaches to determine architecture when
            # the registration does not specify it.
            print('SysArchitecture:', get_value(tag_key, 'SysArchitecture') or '(unknown)')

        try:
            ip_key = winreg.OpenKey(company_key, tag + '\\InstallPath')
        except FileNotFoundError:
            pass
        else:
            with ip_key:
                ip = get_value(ip_key, None)
                exe = get_value(ip_key, 'ExecutablePath') or os.path.join(ip, 'python.exe')
                exew = get_value(ip_key, 'WindowedExecutablePath') or os.path.join(ip, 'python.exe')
                print('InstallPath:', ip)
                print('ExecutablePath:', exe)
                print('WindowedExecutablePath:', exew)
        print()

HKEY_CURRENT_USER\Software\Python\PythonCore
    (Default) = (value not set)
    DisplayName = "Python Software Foundation"
    SupportUrl = "https://pythonlang.cn/"

HKEY_CURRENT_USER\Software\Python\PythonCore\3.6
    (Default) = (value not set)
    DisplayName = "Python 3.6 (64-bit)"
    SupportUrl = "https://pythonlang.cn/"
    Version = "3.6.0"
    SysVersion = "3.6"
    SysArchitecture = "64bit"

HKEY_CURRENT_USER\Software\Python\PythonCore\3.6\Help\Main Python Documentation
    (Default) = "C:\Users\Me\AppData\Local\Programs\Python\Python36\Doc\python360.chm"
    DisplayName = "Python 3.6.0 Documentation"

HKEY_CURRENT_USER\Software\Python\PythonCore\3.6\InstallPath
    (Default) = "C:\Users\Me\AppData\Local\Programs\Python\Python36\"
    ExecutablePath = "C:\Users\Me\AppData\Local\Programs\Python\Python36\python.exe"
    WindowedExecutablePath = "C:\Users\Me\AppData\Local\Programs\Python\Python36\pythonw.exe"