windows-cmd shell doesn't reflect _winreg changes

[Ben Hutchings]

In article <b6e56f7a.0304021609.521700e6 at posting.google.com>, haughki wrote:
> hi
> 
> i'm using _winreg to 'hard-change' and environmental variable in
> windows.  the change is 'successful': regedit correctly reflects the
> changes, and crtl panel > system > properties envronmental vars have
> been correctly changed.  but, when i start a cmd shell (dos), the
> shell evironment still reflects the old values until i manually open
> the env vars cntrl panel and click 'ok'.  anyone?

This is really a Win32 programming issue rather than a Python one.
However, I do vaguely remember this one.

Environmental variables are normally passed to a new process by the
process that creates it, and they can never be updated from outside
a process.  The exception to this is that Windows Explorer (and any
other program that wishes to) will read those initial environment
variables out of the registry when notified of a change in settings.
The changes will then be passed on to any program started by Explorer
afterwards.

Here's the Python code:

    import win32con, win32gui
    win32gui.SendMessage(
        win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 0)

You might want to use SendMessageTimeout instead of SendMessage.