C:\Python25\python.exe D:/PycharmProjects/imit_r_qt4/src/main.py
Traceback (most recent call last):
  File "D:/PycharmProjects/imit_r_qt4/src/main.py", line 20, in <module>
    subwindow.setWidget(prm_from)
TypeError: argument 1 of QMdiSubWindow.setWidget() has an invalid type

# -*- coding: utf-8 -*-
from PyQt4 import QtCore, QtGui
from PyQt4.QtGui import QMdiSubWindow
from imitatorr import Ui_MainWindow
from prm import Ui_Form


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)

    Form = QtGui.QWidget()
    prm_from = Ui_Form()

    subwindow = QMdiSubWindow()

    subwindow.setWidget(prm_from)

    ui.mdiArea.addSubWindow(subwindow)
    MainWindow.show()
    sys.exit(app.exec_())