import sys
from PyQt4 import Qt

class Window(Qt.QMainWindow) :
    def __init__(self, parent=None) :
        Qt.QMainWindow.__init__(self, parent)

        wg = Qt.QWidget()
        line = Qt.QLineEdit()

        layout = Qt.QVBoxLayout()
        layout.addWidget(line)

        wg.setLayout(layout)

        self.setCentralWidget(wg)


app = Qt.QApplication(sys.argv)
w = Window()
w.show()
app.exec_()