Python Forum

I was trying to take a screenshot of a hidden window so I found the code below. But there are so many new terms I don't understand.
Can anyone explain what the device context is? Is it like an address of an image in a monitor device or printer?
if so why I can't directly get the content from the address(DC) and save as a var of bitmap and convert it to png and save it?
Instead, they did it like this:

import win32gui
import win32ui
from ctypes import windll
from PIL import Image

hwnd = win32gui.FindWindow(None, 'Calculator')

left, top, right, bot = win32gui.GetWindowRect(hwnd)
w = right - left
h = bot - top

hwndDC = win32gui.GetWindowDC(hwnd)
#^^^HERE^^^ now I've got the DC handle (hwndDC) can't I just extract image content from it?

mfcDC  = win32ui.CreateDCFromHandle(hwndDC)
#^^^HERE^^^ why create a new DC? what's the relationship of this new DC with the DC obj from hwndDC

saveDC = mfcDC.CreateCompatibleDC()
#^^^HERE^^^ this has the same type as mfcDC but this seems to be called a memory device context, what for?

saveBitMap = win32ui.CreateBitmap()
saveBitMap.CreateCompatibleBitmap(mfcDC, w, h)
#^^^HERE^^^Shouldn't it create bitmap from the DC obj of hwndDC instead of mfcDC

saveDC.SelectObject(saveBitMap)

result = windll.user32.PrintWindow(hwnd, saveDC.GetSafeHdc(), 2)
#^^^HERE^^^ What is this for?

bmpinfo = saveBitMap.GetInfo()
bmpstr = saveBitMap.GetBitmapBits(True)

im = Image.frombuffer(
    'RGB',
    (bmpinfo['bmWidth'], bmpinfo['bmHeight']),
    bmpstr, 'raw', 'BGRX', 0, 1)

im.save('img.png')

win32gui.DeleteObject(saveBitMap.GetHandle())
saveDC.DeleteDC()
mfcDC.DeleteDC()
win32gui.ReleaseDC(hwnd, hwndDC)

Sorry about so many question but I'm really confused