What process owns a certain window (Mac OS X)

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This popped up on my screen, leaving me wondering which process actually drew the window:


It's the UserNotificationCenter app and here's how you can tell:

#!/usr/bin/env python

import time
from Quartz import CGWindowListCopyWindowInfo, kCGWindowListExcludeDesktopElements, kCGNullWindowID
from Foundation import NSSet, NSMutableSet

wl1 = CGWindowListCopyWindowInfo(kCGWindowListExcludeDesktopElements, kCGNullWindowID)
print 'Move target window'
time.sleep(5)
wl2 = CGWindowListCopyWindowInfo(kCGWindowListExcludeDesktopElements, kCGNullWindowID)

w = NSMutableSet.setWithArray_(wl1)
w.minusSet_(NSSet.setWithArray_(wl2))
print '\nList of windows that moved:'
print w
print '\n'

The script prints information for the window that changed position within a 5 second interval.
The output looks like this:

List of windows that moved:
{(
        {
        kCGWindowAlpha = 1;
        kCGWindowBounds =         {
            Height = 217;
            Width = 420;
            X = 828;
            Y = 213;
        };
        kCGWindowIsOnscreen = 1;
        kCGWindowLayer = 8;
        kCGWindowMemoryUsage = 406420;
        kCGWindowName = "";
        kCGWindowNumber = 77;
        kCGWindowOwnerName = UserNotificationCenter;
        kCGWindowOwnerPID = 481;
        kCGWindowSharingState = 1;
        kCGWindowStoreType = 2;
    }
)}