import sys

from PyQt4.QtCore import *
from PyQt4.QtGui import *

from <REPLACE_BY_PYUI_DESIGN> import <REPLACE_BY_WINDOW_CLASS_IN_PYUI_DESIGN>

class MainWindow(QMainWindow, <REPLACE_BY_WINDOW_CLASS_IN_PYUI_DESIGN>):

    # custom slot
    def mymethod(self):
        self.textFieldExample.setText('Hello World')
        self.textFieldExample.clear()

    def __init__(self):
        QMainWindow.__init__(self)
      
       # set up User Interface (widgets, layout...)
        self.setupUi(self)
        # custom slots connections
        QObject.connect(self.pushButton,SIGNAL("released()"),self.mymethod) # signal/slot connection
    
# Main entry to program.  Sets up the main app and create a new window.
def main(argv):
   
    # create Qt application
    app = QApplication(argv,True)
 
    # create main window
    wnd = MainWindow() # classname
    wnd.show()
    
    # Connect signal for app finish
    app.connect(app, SIGNAL("lastWindowClosed()"), app, SLOT("quit()"))
    
    # Start the app up
    sys.exit(app.exec_())
 
if __name__ == "__main__":
    main(sys.argv)

import sys

from PyQt4.QtCore import *
from PyQt4.QtGui import *

from <REPLACE_BY_PYUI_DESIGN> import <REPLACE_BY_WINDOW_CLASS_IN_PYUI_DESIGN>

class MainWindow(QMainWindow, <REPLACE_BY_WINDOW_CLASS_IN_PYUI_DESIGN>):

    # custom slot
    def mymethod(self):
        self.textFieldExample.setText('Hello World')
        self.textFieldExample.clear()

    def __init__(self):
        QMainWindow.__init__(self)
      
       # set up User Interface (widgets, layout...)
        self.setupUi(self)
        # custom slots connections
        QObject.connect(self.pushButton,SIGNAL("released()"),self.mymethod) # signal/slot connection
    
# Main entry to program.  Sets up the main app and create a new window.
def main(argv):
   
    # create Qt application
    app = QApplication(argv,True)
 
    # create main window
    wnd = MainWindow() # MainWindow objectname
    wnd.show()
    
    # Connect signal for app finish
    app.connect(app, SIGNAL("lastWindowClosed()"), app, SLOT("quit()"))
    
    # Start the app up
    sys.exit(app.exec_())
 
if __name__ == "__main__":
    main(sys.argv)

first design your app and generate a .UI file using Designer (part of Qt Creator), then run pyuic4 to get it to python, like:
pyuic4-2.6 example.ui > example.py

then import the window classes in example.py and make your up by subclassing like you can see in the source

Qt GUI app in python with pyqt (subclassing pyuic4 generated file)

python

Python