Custom Widget PyQt

Question

I am trying to create a custom widget and adding it to a listwidget following the example here but used a widget as here(Answer) instead of the progress bar. The custom widget works fine independently. But when it is added to the list widget, the horizontal scrolling works perfect but the vertical scroll covers only a portion of the image. Can somebody suggest some improvement?

The code is

import sys
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 MainWidget(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.scene = QtGui.QGraphicsScene()
        self.view = QtGui.QGraphicsView(self.scene)
        layout = QtGui.QVBoxLayout()
        layout.addWidget(self.view)
        self.setLayout(layout)
        self.pixmap_item = QtGui.QGraphicsPixmapItem(QtGui.QPixmap('image.png'), None, self.scene)

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(800, 600)
        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Preferred, QtGui.QSizePolicy.Preferred)
        sizePolicy.setHorizontalStretch(0)
        sizePolicy.setVerticalStretch(0)
        sizePolicy.setHeightForWidth(MainWindow.sizePolicy().hasHeightForWidth())
        MainWindow.setSizePolicy(sizePolicy)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.listWidget = QtGui.QListWidget(self.centralwidget)
        self.listWidget.setGeometry(QtCore.QRect(170, 20, 400, 400))
        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Fixed, QtGui.QSizePolicy.Fixed)
        sizePolicy.setHorizontalStretch(0)
        sizePolicy.setVerticalStretch(0)
        sizePolicy.setHeightForWidth(self.listWidget.sizePolicy().hasHeightForWidth())
        self.listWidget.setSizePolicy(sizePolicy)
        self.listWidget.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAsNeeded)
        self.listWidget.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAsNeeded)
        self.listWidget.setObjectName(_fromUtf8("listWidget"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(40, 200, 113, 32))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 22))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow", None))
        self.pushButton.setText(_translate("MainWindow", "PushButton", None))

class MyForm(QtGui.QMainWindow):
  def __init__(self, parent=None):
    QtGui.QWidget.__init__(self, parent)
    self.ui = Ui_MainWindow()
    self.ui.setupUi(self)
    self.ui.pushButton.clicked.connect(self.progress)

  def progress(self):
    item = QtGui.QListWidgetItem(self.ui.listWidget)
    item_widget = MainWidget()
    item.setSizeHint(item_widget.sizeHint())
    self.ui.listWidget.addItem(item)
    self.ui.listWidget.setItemWidget(item,item_widget)

if __name__ == "__main__":
  app = QtGui.QApplication(sys.argv)
  myapp = MyForm()
  myapp.show()
  sys.exit(app.exec_())

and here is the test image: