Вычисление количества дней между датами с помощью компонента QCalendarWidget

Календарь PyQT

#!/usr/bin/python3
 
import sys
from PyQt4 import QtGui, QtCore
 
class Window_Calendar(QtGui.QWidget):
        def __init__(self,parent=None):
                QtGui.QWidget.__init__(self,parent)
                self.setGeometry(300,300,700,300)
                self.setWindowTitle("Calendar")
 
                self.cal = QtGui.QCalendarWidget(self)
                self.cal.setGridVisible(True)
                self.cal.move(20,20)
                self.connect(self.cal,QtCore.SIGNAL('selectionChanged()'),
                                                self.showDate)
 
                self.cal1 = QtGui.QCalendarWidget(self)
                self.cal1.setGridVisible(True)
                self.cal1.move(350,20)
                self.connect(self.cal1,QtCore.SIGNAL('selectionChanged()'),
                                                self.showDate)
 
                self.label = QtGui.QLabel(self)
                date = self.cal.selectedDate()
                self.label.setText(str(date.toPyDate()))
                self.label.move(130,230)
 
                self.label1 = QtGui.QLabel(self)
                date1 = self.cal1.selectedDate()
                self.label1.setText(str(date1.toPyDate()))
                self.label1.move(430,230)
 
 
                self.label2 = QtGui.QLabel(self)
                self.label2.setText(str(date.toPyDate()-date1.toPyDate()))
                self.label2.move(300,250)
 
        def showDate(self):
                date = self.cal.selectedDate()
                self.label.setText(str(date.toPyDate()))
                date1 = self.cal1.selectedDate()
                self.label1.setText(str(date1.toPyDate()))      
 
                a = date.toPyDate() # type: <class 'datetime.date'>
                b = date1.toPyDate()
                c = b - a
                c = str(c) 
                if c[0] == '-': c = c[1:] 
                c = c.split()[0] 
                self.label2.setText(c)  
 
app = QtGui.QApplication(sys.argv)
window = Window_Calendar()
window.show()
app.exec_()