from PyQt4 import QtCore, QtGui

class Unterfenster(QtGui.QWidget):

def Unterfenster_schliessen(self):
Form1.lineEdit.clear()
Form1.lineEdit.setFocus()
self.close()


if __name__ == "__main__":
import sys
app = QtGui.QApplication(sys.argv)
Form1 = Hauptfenster()
Form1.show()
sys.exit ...