from PyQt4 import QtCore, QtGui
import sys, os, time

app = QtGui.QApplication(sys.argv)
window = QtGui.QWidget()

message = QtGui.QPlainTextEdit('Please, type any text here...')
slider = QtGui.QSlider(QtCore.Qt.Horizontal)
slider.setTickPosition(QtGui.QSlider.TicksBelow)
slider.setRange(0, 6)
slider.setTracking(False)

l = QtGui.QVBoxLayout()
l.addWidget(message)
l.addWidget(slider)
window.setLayout(l)

def slider_change():
    text = message.toPlainText()
    if slider.value() == 0:
        message.setPlainText(text)

    if slider.value() == 1:
         message.setReadOnly(True)
         m = str(message.toPlainText())
         translated = ''
         i = len(m) - 1
         while i >= 0:
            translated = translated + m[i]
            i = i - 1
            message.setPlainText(translated)


QtCore.QObject.connect(slider, QtCore.SIGNAL('valueChanged(int)'),
                        slider_change)
window.show()
sys.exit(app.exec_())