Python - Windows Shutdown Events

The problem here was that the HWND_MESSAGE window type doesn't actually receive broadcast messages - like the WM_QUERYENDSESSION and WM_ENDSESSION.

So instead of specifying win32con.HWND_MESSAGE for the "parent window" parameter of CreateWindowEx(), I just specified 0.

Basically, this creates an actual window, but I never show it, so it's effectively the same thing. Now, I can successfully receive those broadcast messages and shut down the app properly.

Detect shutdown event with python

So, what you will need is the win32API and the function described here. You can use this function to add what's called a Control Handler Method that will run whenever the program is being shut down or terminated for any reason, including shutdown. You can find a list of the different codes that can be passed to the handler and their meanings here. Ideally, you should have a handler method that just shuts down the server, waits for it to finish shutting down, and then return.

I don't have any personal experience with the library, but it should be fairly straightforward.

EDIT: as noted by @ErykSun, you will need to create a hidden window in order to receive the events. To be quite honest I'm not sure how to create that hidden window. Some documentation suggests that running your application as a service may also work. I will look into this more if I get time.

Python handling system shutdown

A nabble.com page suggests using win32api.SetConsoleCtrlHandler:

“I need to do something when windows shuts down, as when someone presses the power button. I believe this is a window message, WM_QUERYENDSESSION or WM_ENDSESSION. I can't find any way to trap this in python. atexit() does not work. Using the signal module to trap SIGBREAK or SIGTERM does not work either.”

You might be able to use win32api.SetConsoleCtrlHandler and catch the CTRL_SHUTDOWN_EVENT that's sent to the console.

Also see Python windows shutdown events, which says, “When using win32api.setConsoleCtrlHandler() I'm able to receive shutdown/logoff/etc events from Windows, and cleanly shut down my app” etc.

Detecting computer/program shutdown in Python?

You should react to the WM_ENDSESSION message.

This message is sent when the user logs off or the computer gets shut down.

If you want to react to Sleep/Hibernate as well, you'll need to handle WM_POWERBROADCAST with PBT_APMSUSPEND.

But I don't know how to do that in python. I guess it depends on your windowing framework since you need have a windows/a message loop to receive messages.

trigger a function when pc is shutting down - tkinter

I am not aware of Tkinter having a specific tool to catch system shutdowns like you suggest. You would be better registering a signal handler that can catch the shutdown signal and trigger the in_close function.

(Also worth looking here for some extra details)

import signal

def in_close(signum = None, frame = None):
    # Here you can attempt to gently exit your application.
    pass

# For some common signals that will close your program.
for sig in [signal.SIGTERM, signal.SIGINT, signal.SIGHUP, signal.SIGQUIT]:
    signal.signal(sig, in_close)

As pointed out in the comments, this is not a Windows valid solution. For discussions on handling windows shutdown events see:

Python - Windows Shutdown Events

Python - Windows Shutdown Events