#!/usr/bin/python

# Convenience imports
from PyQt4.QtCore import *
from PyQt4.QtGui import *

import sys

# This is a decorator class
class WinUi:
  # With only one function to decorate a window
  def setupUi(self, parent):
    self.centralwidget=QWidget(parent)
    parent.setCentralWidget(self.centralwidget)

    # A horizontal layout
    self.layout=QHBoxLayout(self.centralwidget)
   
    # With three items
    self.label=QLabel("Name:", self.centralwidget)
    self.txt=QLineEdit(self.centralwidget)
    self.but=QPushButton(self.centralwidget)

    l=self.layout

    # Add them to the layout
    l.addWidget(self.label)
    l.addWidget(self.txt)
    l.addWidget(self.but)
        
    # Se the label of the button
    self.but.setText("OK")

class Win(QMainWindow):
  def __init__(self):
    QMainWindow.__init__(self)

    # Setup the UI using the decorator class
    self.ui=WinUi()
    self.ui.setupUi(self)

    # Connect the mouse "clicked" event to a function
    self.ui.but.clicked.connect(self.click)

  def click(self):
    txt=self.ui.txt.text()
    if txt=='':
      QMessageBox.critical(self, "Error", "Please type something")
    else:
      QMessageBox.information(self, "Success", "You typed: %s" % txt)

# Standard things
# Create an application then create a window.
# Show the window and run the main loop
app=QApplication(sys.argv)
win=Win()
win.show()
app.exec_()

python myfile.py