http://nikolak.com/pyqt-qt-designer-getting-started/

design.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'design.ui'
#
# Created: Wed May 27 16:39:17 2015
#      by: PyQt4 UI code generator 4.11.3
#
# WARNING! All changes made in this file will be lost!

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(240, 345)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.verticalLayout = QtGui.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName(_fromUtf8("verticalLayout"))
        self.listWidget = QtGui.QListWidget(self.centralwidget)
        self.listWidget.setObjectName(_fromUtf8("listWidget"))
        self.verticalLayout.addWidget(self.listWidget)
        self.btnBrowse = QtGui.QPushButton(self.centralwidget)
        self.btnBrowse.setObjectName(_fromUtf8("btnBrowse"))
        self.verticalLayout.addWidget(self.btnBrowse)
        MainWindow.setCentralWidget(self.centralwidget)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow", None))
        self.btnBrowse.setText(_translate("MainWindow", "Pick a folder", None))

design.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>240</width>
    <height>345</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <layout class="QVBoxLayout" name="verticalLayout">
    <item>
     <widget class="QListWidget" name="listWidget"/>
    </item>
    <item>
     <widget class="QPushButton" name="btnBrowse">
      <property name="text">
       <string>Pick a folder</string>
      </property>
     </widget>
    </item>
   </layout>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>

main.py

from PyQt4 import QtGui  # Import the PyQt4 module we'll need
import sys  # We need sys so that we can pass argv to QApplication

import design  # This file holds our MainWindow and all design related things

# it also keeps events etc that we defined in Qt Designer
import os  # For listing directory methods


class ExampleApp(QtGui.QMainWindow, design.Ui_MainWindow):
    def __init__(self):
        # Explaining super is out of the scope of this article
        # So please google it if you're not familar with it
        # Simple reason why we use it here is that it allows us to
        # access variables, methods etc in the design.py file
        super(self.__class__, self).__init__()
        self.setupUi(self)  # This is defined in design.py file automatically
        # It sets up layout and widgets that are defined
        self.btnBrowse.clicked.connect(self.browse_folder)  # When the button is pressed
                                                            # Execute browse_folder function

    def browse_folder(self):
        self.listWidget.clear() # In case there are any existing elements in the list
        directory = QtGui.QFileDialog.getExistingDirectory(self,
                                                           "Pick a folder")
        # execute getExistingDirectory dialog and set the directory variable to be equal
        # to the user selected directory

        if directory: # if user didn't pick a directory don't continue
            for file_name in os.listdir(directory): # for all files, if any, in the directory
                self.listWidget.addItem(file_name)  # add file to the listWidget


def main():
    app = QtGui.QApplication(sys.argv)  # A new instance of QApplication
    form = ExampleApp()  # We set the form to be our ExampleApp (design)
    form.show()  # Show the form
    app.exec_()  # and execute the app


if __name__ == '__main__':  # if we're running file directly and not importing it
    main()  # run the main function

MAny thanks

Hi, I followed your instructions but I got following Error can you please help. 
File "test.py", line 20, in main     form = ExampleApp()                 # We set the form to be our ExampleApp (design)   File "test.py", line 14, in __init__     self.setupUi(self)  # This is defined in design.py file automatically   File "D:\Present work\product\maint.py", line 1418, in setupUi     QtCore.QObject.connect(self.close, QtCore.SIGNAL(_fromUtf8("triggered()")), MainWindow.close) TypeError: arguments did not match any overloaded call:   QObject.connect(QObject, SIGNAL(), QObject, SLOT(), Qt.ConnectionType=Qt.AutoConnection): not enough arguments   QObject.connect(QObject, SIGNAL(), callable, Qt.ConnectionType=Qt.AutoConnection): argument 3 has unexpected type 'QAction'   QObject.connect(QObject, SIGNAL(), SLOT(), Qt.ConnectionType=Qt.AutoConnection): argument 2 has unexpected type 'bytes'

Any help would be appreciated.

Hello would you please update your blog, you need to clarify that your code will not work on PyQt5 environment.
The QtGui is not supported in PyQt5, it needs to be changed using QtWidgets instead.

This is the code updated to work with PyQt5
CODE
from PyQt5 import QtGui, QtCore, QtWidgets
import sys, os

import design

class ExampleApp(QtWidgets.QMainWindow, design.Ui_MainWindow):
def init(self, parent=None):
super(ExampleApp, self).init(parent)
self.setupUi(self)
self.btnBrowse.clicked.connect(self.browse_folder)

def browse_folder(self):
    self.listWidget.clear()
    directory = QtWidgets.QFileDialog.getExistingDirectory(self,"Pick a folder")
    if directory:
        for file_name in os.listdir(directory):
            self.listWidget.addItem(file_name)

def main():
app = QtWidgets.QApplication(sys.argv)
form = ExampleApp()
form.show()
app.exec()

if name == 'main':
main()
CODE

Thanks

Thank you very much!