Pythonic interface to the global and user environment variables on Windows.

win_env.py

# This is free and unencumbered software released into the public domain.
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"""Get global Windows environment variables.

This can be useful for programs that need to spawn subprocesses, 
but want to make sure that those subprocess are always spawned
with the latest changes from the global environment variables."""




import os
import winreg
import collections.abc


def _dump_vars(root_key, reg_path, expand_envars=True):
    with winreg.OpenKey(root_key, reg_path) as reg_key:
        rval = {}
        r = range(winreg.QueryInfoKey(reg_key)[1])
        for v in (winreg.EnumValue(reg_key, i) for i in r):
            if expand_envars and v[2] == winreg.REG_EXPAND_SZ:
                rval[v[0]] = winreg.ExpandEnvironmentStrings(v[1])
            else:
                rval[v[0]] = v[1]
        return rval


def dump_win_env(system=True, user=True, expand_envars=True, combine_path=True):
    rdict = dict()
    sdict = dict()
    udict = dict()

    if system:
        root_key = winreg.HKEY_LOCAL_MACHINE
        reg_path = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
        sdict = _dump_vars(root_key, reg_path, expand_envars=expand_envars)

    if user:
        root_key = winreg.HKEY_CURRENT_USER
        reg_path = r'Environment'
        udict = _dump_vars(root_key, reg_path, expand_envars=expand_envars)

    rdict.update(sdict)
    rdict.update(udict)

    path_names = [n for n in rdict.keys() if n.casefold() == 'Path'.casefold()]
    path_name = path_names[0] if path_names else 'Path'
    if combine_path and system and user and path_name in sdict and path_name in udict:
        spath = sdict[path_name].strip(os.pathsep)
        upath = udict[path_name].strip(os.pathsep)
        rdict[path_name] = os.pathsep.join([spath, upath])

    return rdict

# Useful links for how to do certain things related to the Registry in Windows:
#
# Request UAC elevation from within a Python script? This is useful if one
# wants/needs to modify protected registry entries, such as system (not user)
# global variables:
# * https://stackoverflow.com/a/41930586/1733321
#
# How to notify other processes of global environment variable changes. Also,
# how to set key values:
# * https://stackoverflow.com/a/21472285/1733321
#
# How to get environment variables from the registry based on given key. Useful
# for `__getitem__`, `__setitem__`, and `__delitem__` implementations:
# * https://stackoverflow.com/a/37547237/1733321
#
# How to loop thru/enumerate keys/values for a given registry key. Useful for
# `__len__` and `__iter__` implementations of a Mapping class:
# * https://stackoverflow.com/q/3974038/1733321

class WinEnv(collections.abc.Mapping):
    def __init__(self, system=False):
        if system:
            root_key = winreg.HKEY_LOCAL_MACHINE
            reg_path = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
        else:
            root_key = winreg.HKEY_CURRENT_USER
            reg_path = r'Environment'

        self._cache = _dump_vars(root_key, reg_path)

    def __getitem__(self, key):
        return self._cache[key]

    def __iter__(self):
        return iter(self._cache)

    def __len__(self):
        return len(self._cache)

    def to_dict(self):
        return dict(self)