I just wanted to test and show something about processEvents

qtexample.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
import time
from PyQt4 import QtGui, QtCore

app = QtGui.QApplication(sys.argv)

widget = QtGui.QWidget()
widget.resize(250, 150)
widget.setWindowTitle('Hello, World!')

te = QtGui.QTextEdit(widget)

def append():
    i = 0
    while True:
        te.append(" %d" % i)
        i += 1
        time.sleep(0.5)
        app.processEvents() # <<<

btn = QtGui.QPushButton("Append", widget)
widget.connect(btn, QtCore.SIGNAL('clicked()'),
            append)


widget.show()

sys.exit(app.exec_())