在 PyQt4 中计算两个值

Question

我无法弄清楚这个问题： self.calcbtn = int(self.a + self.b)

import sys
from PyQt4 import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        self.a = QtGui.QLabel('A')
        self.b = QtGui.QLabel('B')
       

        aEdit = QtGui.QLineEdit()
        bEdit = QtGui.QLineEdit()
       
       
        calcbtn = QtGui.QPushButton("result")
       

        grid = QtGui.QGridLayout()
        grid.setSpacing(10)

        grid.addWidget(self.a, 1, 0)
        grid.addWidget(aEdit, 1, 1)

        grid.addWidget(self.b, 2, 0)
        grid.addWidget(bEdit, 2, 1)
        grid.addWidget(calcbtn, 4, 0)
        self.calcbtn = int(self.a + self.b)
       

      
        
        
        self.setLayout(grid) 
        
        self.setGeometry(300, 300, 350, 300)
            
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()