env variable set using _winreg.SetValueEx() doesn't show w/ os.environ

Matt Gerrans matt.gerrans at hp.com
Tue Dec 16 22:16:48 CET 2003

Here is what I do; it works well on WinXP/2K/NT and with Python 2.2 and 2.3.
(Of course, it wouldn't work for a "limited user" account -- for that case,
it could be modified to use HKEY_CURRENT_USER instead, but it would only be
able to change the "user variables" not the system variables).   The code
below is for updating the path variable, but you can modify it to work for
any variable.

Also, as you may know, this doesn't change the variable settings for the
current process, just for all new processes and those few smart ones that
actually pay attention to the broadcast message.   If you want to also
change variables for a sub-process you are launching, then additiobnally
modifing those via os.environ will do the trick.   If you want to add/modify
variables for a process that runs *after* yours (in a shell script, for
example), that's the tough one (but it can "kind of" be done by jumping
through some silly hoops).

Appends a chunk to the path in a way that puts it in effect as soon as

Command line syntax:
   appendToSystemPath [some part to append] [another var]

If you specify "another var" it means you want to append that environment
variable instead.   This is only useful if that other variable is a
path-like variable, such as classpath, pythonpath, pathext, etc.
versions = ['','']
version = versions[-1]

from _winreg import *
from win32gui import SendMessageTimeout
from win32con import HWND_BROADCAST
from win32con import WM_SETTINGCHANGE
import os, sys

from win32con import WM_STYLECHANGING
from win32con import WM_STYLECHANGED
from win32con import GWL_EXSTYLE

debug = os.environ.get('debug','0') == '1'

#                             addToSystemPath()
# Dependencies: _winreg, win32api, win32con, os.
# Description:  Adds an item to the system path; currently, the effect will
#               will not be promulgated properly until after a reboot,
#               because the documented method of doing this does not work.
#               The new chunk will only be added if it is not already in the
#               path (a case-insensitive search is done to verify this).
# Parameters:   newPart: The chunk to add to the path.
# Returns:      1 if all went well.
# History:      2002-07-16 mfg: Created; also sent a acrimonious email to
#               Microsoft about thier inadequated documentation with regards
#               to setting system variables.
def addToSystemPath(newPart,item='path'):
   keypath = r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
   result = 1
      if debug: print 'Opening',keypath
      key = OpenKey( HKEY_LOCAL_MACHINE, keypath )
      if debug: print 'Querying',item
      path,dataType = QueryValueEx( key, item )
      print 'Current %s is: %s' % (item,path)
      if path.lower().find(newPart.lower()) == -1:
         if debug: print 'It does not contain',newPart
         path = os.pathsep.join( path.split(os.pathsep) + [newPart] )

         key = OpenKey( HKEY_LOCAL_MACHINE, keypath, 0, KEY_SET_VALUE )
         SetValueEx( key, item, 0, dataType, path )
         print 'Set %s in registry.' % path
         # Windows documentation says that this works, but it doesn't:
         if debug: print 'Broadcasting settings change message...'
         SendMessageTimeout( HWND_BROADCAST, WM_SETTINGCHANGE, 0,
"Environment", 0, 1000 )
         print 'New %s is:' % item
         print path
         print 'Nothing to do -- it is already there!'
      if debug: print 'All done!'
      if debug: print 'Bronk!'
      result = 0
   return result

if __name__ == '__main__':
   if len(sys.argv) > 1:
      if len(sys.argv) > 2:
      print __doc__

"Erick Bodine" <erick_bodine at comcast.net> wrote in message
news:8de75d53.0312161259.5aef3753 at posting.google.com...
> I am trying to set a new environment variable on a W2k machine with
> only partial success.  The name("SSID") and value("ASIM") show up
> correctly in the registry and when I go to "System
> Properties"->Advanced->"Environment Variables".  However, if I open a
> console and type 'set', "SSID" is not listed; also if I open a python
> shell and do os.environ["SSID"] the variable is not found.  What am I
> doing wrong???
> import _winreg
> system = r"SYSTEM\CurrentControlSet\Control\Session
> Manager\Environment"
> registry = _winreg.ConnectRegistry(None, _winreg.HKEY_LOCAL_MACHINE)
> env_key = _winreg.OpenKey(registry, system, 0, _winreg.KEY_SET_VALUE)
> key = "SSID"
> value = "ASIM"
> try:
>     _winreg.SetValueEx(env_key, key, 0, _winreg.REG_EXPAND_SZ, value)
> except EnvironmentError:
>     print "Encountered problems writing (%s) into the registry" % key
> _winreg.CloseKey(env_key)
> _winreg.CloseKey(registry)
> I have tried this using ActivePython-2.3.2-232 and Python-2.3.2 w/ the
> same results.
> Thanks,
> ERick

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