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 not persist once the python interpreter terminates. If I were scripting this on UNIX, I might do something like:

set foo=`myscript.py`

But alas, cmd.exe does not have anything that works like sh's back-tick behavior. I have seen a very long-winded solution... it 'aint pretty so surely we can improve on this:

for /f "tokens=1* delims=" %%a in ('python  ..\myscript.py') do set path=%path%;%%a

Surely the minds at Microsoft have a better solution than this!

Note: exact duplicate of this question.

Answer 1

Your long-winded solution is probably the best idea; I don't believe this is possible from Python directly. This article suggests another way, using a temporary batch file:

http://code.activestate.com/recipes/159462/

Answer 2

You might want to try Python Win32 Extensions,developed by Mark Hammond, which is included in the activestate installer (or can be installed separately). You can learn how to perform many Windows related tasks in Hammond's and Robinson's book.

Using Pywin32 to access windows COM objects, a python program can use the Environment Property of the WScript.Shell object - a collection of environment variables.

Answer 3

Windows sets Environment variables from values stored in the Registry for each process independently.

However, there is a tool in the Windows XP Service Pack 2 Support Tools named setx.exe that allows you to change global Environment variables from the command line.

Answer 4

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 <barmenkov at bpc.ru>

    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\\ControlSet001\\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"