Can a python script persistently change a Windows environment variable? (elegantly)

Question

Following on from my previous question, is it possible to make a Python script which persistently changes a Windows environment variable?

Changes to os.environ do n

Answer 1

My solution using win32api:

import os, sys, win32api, win32con
'''Usage: appendenv.py envvar data_to_append'''
def getenv_system(varname, default=None):
    '''
    Author: Denis Barmenkov 

    Copyright: this code is free, but if you want to use it, 
               please keep this multiline comment along with function source. 
               Thank you.

    2006-01-28 15:30
    '''
    v = default
    try:
        rkey = win32api.RegOpenKey(win32con.HKEY_LOCAL_MACHINE, 'SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment')
        try:
            v = str(win32api.RegQueryValueEx(rkey, varname)[0])
            v = win32api.ExpandEnvironmentStrings(v)
        except:
            pass
    finally:
        win32api.RegCloseKey(rkey)
    return v

#My set function
def setenv_system(varname, value):
    try:
        rkey = win32api.RegOpenKeyEx(win32con.HKEY_LOCAL_MACHINE, 'SYSTEM\\CurrentControlSet\\Control\\Session Manager\\Environment',0 ,win32con.KEY_WRITE)
        try:
            win32api.RegSetValueEx(rkey, varname, 0, win32con.REG_SZ, value)
            return True
        except Exception, (error):
            pass
    finally:
        win32api.RegCloseKey(rkey)
    return False

if len(sys.argv) == 3:
    value = getenv_system(sys.argv[1])
    if value:
        setenv_system(sys.argv[1],value + ";" + sys.argv[2])
        print "OK! %s = %s" % (sys.argv[1], getenv_system(sys.argv[1]))
    else:
        print "ERROR: No such environment variable. (%s)" % sys.argv[1]
else:
    print "Usage: appendenv.py envvar data_to_append"