Interface for modifying Windows environment variables from Python

Question

How can I persistently modify the Windows environment variables from a Python script? (it\'s the setup.py script)

I\'m looking for a standard function or module to u

Answer 1

This Python-script[*] attempts to modify the GLOBAL env-vars in registry, if no-permissions falls-back to user's registry, and then notifies all windows about the change:

"""
Show/Modify/Append registry env-vars (ie `PATH`) and notify Windows-applications to pickup changes.

First attempts to show/modify HKEY_LOCAL_MACHINE (all users), and 
if not accessible due to admin-rights missing, fails-back 
to HKEY_CURRENT_USER.
Write and Delete operations do not proceed to user-tree if all-users succeed.

Syntax: 
    {prog}                  : Print all env-vars. 
    {prog}  VARNAME         : Print value for VARNAME. 
    {prog}  VARNAME   VALUE : Set VALUE for VARNAME. 
    {prog}  +VARNAME  VALUE : Append VALUE in VARNAME delimeted with ';' (i.e. used for `PATH`). 
    {prog}  -VARNAME        : Delete env-var value. 

Note that the current command-window will not be affected, 
changes would apply only for new command-windows.
"""

import winreg
import os, sys, win32gui, win32con

def reg_key(tree, path, varname):
    return '%s\%s:%s' % (tree, path, varname) 

def reg_entry(tree, path, varname, value):
    return '%s=%s' % (reg_key(tree, path, varname), value)

def query_value(key, varname):
    value, type_id = winreg.QueryValueEx(key, varname)
    return value

def show_all(tree, path, key):
    i = 0
    while True:
        try:
            n,v,t = winreg.EnumValue(key, i)
            print(reg_entry(tree, path, n, v))
            i += 1
        except OSError:
            break ## Expected, this is how iteration ends.

def notify_windows(action, tree, path, varname, value):
    win32gui.SendMessage(win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 'Environment')
    print("---%s %s" % (action, reg_entry(tree, path, varname, value)))

def manage_registry_env_vars(varname=None, value=None):
    reg_keys = [
        ('HKEY_LOCAL_MACHINE', r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'),
        ('HKEY_CURRENT_USER', r'Environment'),
    ]
    for (tree_name, path) in reg_keys:
        tree = eval('winreg.%s'%tree_name)
        try:
            with winreg.ConnectRegistry(None, tree) as reg:
                with winreg.OpenKey(reg, path, 0, winreg.KEY_ALL_ACCESS) as key:
                    if not varname:
                        show_all(tree_name, path, key)
                    else:
                        if not value:
                            if varname.startswith('-'):
                                varname = varname[1:]
                                value = query_value(key, varname)
                                winreg.DeleteValue(key, varname)
                                notify_windows("Deleted", tree_name, path, varname, value)
                                break  ## Don't propagate into user-tree.
                            else:
                                value = query_value(key, varname)
                                print(reg_entry(tree_name, path, varname, value))
                        else:
                            if varname.startswith('+'):
                                varname = varname[1:]
                                value = query_value(key, varname) + ';' + value
                            winreg.SetValueEx(key, varname, 0, winreg.REG_EXPAND_SZ, value)
                            notify_windows("Updated", tree_name, path, varname, value)
                            break  ## Don't propagate into user-tree.
        except PermissionError as ex:
            print("!!!Cannot access %s due to: %s" % 
                    (reg_key(tree_name, path, varname), ex))
        except FileNotFoundError as ex:
            print("!!!Cannot find %s due to: %s" % 
                    (reg_key(tree_name, path, varname), ex))

if __name__=='__main__':
    args = sys.argv
    argc = len(args)
    if argc > 3:
        print(__doc__.format(prog=args[0]))
        sys.exit()

    manage_registry_env_vars(*args[1:])

Below are some usage examples, assuming it has been saved in a file called setenv.py somewhere in your current path. Note that in these examples i didn't have admin-rights, so the changes affected only my local user's registry tree:

> REM ## Print all env-vars
> setenv.py
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
HKEY_CURRENT_USER\Environment:PATH=...
...

> REM ## Query env-var:
> setenv.py PATH C:\foo
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
!!!Cannot find HKEY_CURRENT_USER\Environment:PATH due to: [WinError 2] The system cannot find the file specified

> REM ## Set env-var:
> setenv.py PATH C:\foo
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Set HKEY_CURRENT_USER\Environment:PATH=C:\foo

> REM ## Append env-var:
> setenv.py +PATH D:\Bar
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Set HKEY_CURRENT_USER\Environment:PATH=C:\foo;D:\Bar

> REM ## Delete env-var:
> setenv.py -PATH
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Deleted HKEY_CURRENT_USER\Environment:PATH

[*] Adapted from: http://code.activestate.com/recipes/416087-persistent-environment-variables-on-windows/