Script to presistently set environment vars on Windows

persistantWindowsEnvVars.py

from _winreg import *
import os, sys, win32gui, win32con

class Penv:
	def __init__(self):
		path = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
		self.reg = ConnectRegistry(None, HKEY_LOCAL_MACHINE)
		self.regKey = OpenKey(self.reg, path, 0, KEY_ALL_ACCESS)

	def query(self, name):       
		value, type_id = QueryValueEx(self.regKey, name)
		return value

	def set(self, name, value):
		if name.upper() == 'PATH':
			value = self.query(name) + ';' + value
		SetValueEx(self.regKey, name, 0, REG_EXPAND_SZ, value)

	def delete(self, name):
		DeleteValue(self.regKey, name)

	def show(self):
		for i in range(1024):                                           
			try:
				n,v,t = EnumValue(self.regKey, i)
				print '%s=%s' % (n, v)
			except EnvironmentError:
				break

	def __del__(self):
		win32gui.SendMessage(win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 'Environment')
		CloseKey(self.regKey)    
		CloseKey(self.reg)

def main():
    try:
        e = Penv() 
        if len(sys.argv) == 1:
            e.show()
        else:
            name, value = sys.argv[1].split('=')
            if value:
				e.set(name, value)
            else:
                e.delete(name)
    except Exception, ex:
        print ex 
    
if __name__=='__main__':    
    usage = \
"""
Usage:

Show all environment variables:
	$ pyhton env.py
Add/Modify/Delete environment variable
	$ python env.py <name>=[value]

If <name> is PATH env.py will append the value prefixed with ;

If there is no value env.py will delete the <name> environment variable

Note that the current command window will not be affected, 
only new command windows.
"""
    argc = len(sys.argv)
    if argc > 2 or (argc == 2 and sys.argv[1].find('=') == -1):
        print usage
        sys.exit()
        
    main()

# Using this script taken form the ASPN cookbook really helped me grok somme important questions.
# It was a plain procedural script, with the registry tree passed to every fonction. Using a class
# allowed me to:
# - exploit RAII (Resource acquisition is initialisation ): the connection to the registry is opened
#   when the objet is instantiated, and destroyed when the instance goes out of scope.
# - get rid of somme globals, by making them instance attributes