import os , time, win32gui

from subprocess import Popen

from PyQt5 import QtWidgets

# root_dir = os.environ.get("SystemRoot",r"C:\\WINDOWS")
# calc = r'%s\\System32\\calc.exe' % root_dir
# Popen(calc)
# time.sleep(1)
#Get window handle of calc window
calc_hwnd = win32gui.FindWindow(None, u"C:\WINDOWS\system32\cmd.exe")
print(calc_hwnd)
#Creat QT Application
a = QtWidgets.QApplication([])
mainwin = QtWidgets.QMainWindow()
#Set QT mainwindow as parent of calc window
print(int(mainwin.winId()))
win32gui.SetParent(calc_hwnd, int(mainwin.winId()))

mainwin.showMaximized()
mainwin.show()
#Convert calc into QT widget
wgt = mainwin.find(calc_hwnd)
#XXX: following print gives "None"
print (type(wgt))
a.exec_()