from PyQt4.Qt import *
def pressed():
    label.setText(edit.text())
if __name__ == "__main__":
    app = QApplication([])
    label = QLabel()
    label.resize(300,50)
    edit = QLineEdit()
    edit.returnPressed.connect(pressed)
    label.move(0,0)
    edit.move(0,100)
    label.show()
    edit.show()
    app.exec_()

 from PyQt4.Qt import *
import sys
class W(QWidget):
    def __init__(self,parent=None):
        QWidget.__init__(self)
        self.edit = QLineEdit()
        self.btn = QPushButton('Push')
        layout = QVBoxLayout(self)
        layout.addWidget(self.edit)
        layout.addWidget(self.btn)
        
def btnClicked():
    if w2.isVisible(): w2.hide()
    elif w2.isHidden(): w2.show()
def editPressed():
    w1.edit.setText(w2.edit.text())
    
def app_quit():
    sys.exit()
    
if __name__ == "__main__":
    app = QApplication([])
    app.lastWindowClosed.connect(app_quit)
    w1 = W()
    w1.edit.setReadOnly(True)
    w2 = W()
    w2.btn.setEnabled(False)
    w1.btn.clicked.connect(btnClicked)
    w2.edit.returnPressed.connect(editPressed)
    w1.move(100,100)
    w1.show()
    app.exec_()