How to capture a single window, not the full screen

[random-developer]

Is autopy able to capture the image of a single window? Alternatively, is there a way to tell autopy.bitmap a height/width/set of bits to have it build a bitmap (without needing to go through the file system)?

For context, on macOS you can get a CGImage of just a specific window if you know its window Id:

from Quartz import CGWindowListCreateImage, CGRectNull, kCGWindowListOptionIncludingWindow, kCGWindowImageBoundsIgnoreFraming, kCGWindowImageNominalResolution
def imageOfWindow(windowId):
    return CGWindowListCreateImage(CGRectNull, kCGWindowListOptionIncludingWindow, windowId, kCGWindowImageBoundsIgnoreFraming|kCGWindowImageNominalResolution)

and it would be nice to be able to use autopy's bitmap searching on that. From the CGImageRef I could write the image to a png file and then read it into autopy but that's wasteful.