dialog - Pyside 代码不显示任何内容

Question

请有人告诉我为什么这段代码似乎确实有效。那就是至少显示一个对话框。

import sys
from PySide.QtCore import *
from PySide.QtGui import *

class Form(QDialog):
def _init_(self,parent = None):
    super(Form , self).__init__(parent)

    self.numberLabel1 = QLabel("first Number")
    self.numberLabel2 = QLabel("Second Number")
    self.txtField1 = QLineEdit() 
    self.txtField2 = QLineEdit()
    self.btnSum = QPushButton("Sum")
    self.resultKeep = QLabel()

    grid = QGridLayout()

    grid.addWidget(self.numberLabel1,0,0) 
    grid.addWidget(self.txtField1,0,1)
    grid.addWidget(self.numberLabel2,1,0)
    grid.addWidget(self.txtField2,1,1)
    grid.addWidget(self.resultKeep,0,2)
    grid.addWidget(self.btnSum,0,3)
    self.setLayout(grid)
if __name__ == '__init__'    :   
    app = QApplication(sys.a`enter code here`rgv)
    form = Form()
    form.show()        
    #sys.exit(app.exec_())