PyQt多窗口调用

经常有人问到如何在一个主窗口中打开一个对话框，然后在确认对话框之后，开启另一个窗口进行后续操作，
要求主窗口和最终的窗口之间都能响应用户操作，也就是非模态窗口。随手写了几行代码，简要示意。

:::python
#!/usr/bin/python
# -*- coding: utf-8 -*-
# Gui (imgui@qq.com)
# License: BSD

from PyQt4.QtCore import *
from PyQt4.QtGui import *
import sys

class W1(QWidget):
    def __init__(self, parent=None):
        super(W1, self).__init__(parent)
        self.btn = QPushButton('Click1')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)

        self.btn.clicked.connect(self.fireupWindows2)

    def fireupWindows2(self):
        w2 = W2()
        if w2.exec_():
            self.w3 = W3()    # 需要通过self实例化为全局变量，不加self的话，一运行就被回收，也就无法显示。
            self.w3.show()

class W2(QDialog):
    def __init__(self, parent=None):
        super(W2, self).__init__(parent)

        self.btn = QPushButton('Click2')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)

        self.btn.clicked.connect(self.fireupWindows3)

    def fireupWindows3(self):
        self.accept()

class W3(QWidget):
    def __init__(self, parent=None):
        super(W3, self).__init__(parent)
        self.resize(300, 300)
        self.btn = QLabel('The Last Window')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = W1()
    w.show()
    sys.exit(app.exec_())

---

oneMainWindow.py
# -*- coding:utf-8 -*-

from PyQt4.QtGui import (QMainWindow, QPushButton, QApplication, 
                                     QVBoxLayout, QWidget)
from PyQt4.QtCore import (Qt, QObject, SIGNAL)
import anotherWindow
import sys

class OneWindow(QMainWindow):
    def __init__(self):
        super(OneWindow, self).__init__()
        self.setGeometry(100, 100, 600, 400)
        vLayout = QVBoxLayout()
        self.button = QPushButton("OK")
        vLayout.addWidget(self.button)
        widget = QWidget()
        widget.setLayout(vLayout)
        self.setCentralWidget(widget)
        
        QObject.connect(self.button,SIGNAL("clicked()") , self.anotherWindow)
        
    def anotherWindow(self):
        print 'OK'
        self.another = anotherWindow.AnotherWindow()
        self.another.show()              #难道不是用这个show（）函数吗？
    
if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = OneWindow()
    w.show()     
    app.exec_()

anotherWindow.py
# -*- coding:utf-8 -*-

from PyQt4.QtGui import (QMainWindow)

class AnotherWindow(QMainWindow):
    def __init__(self):
        super(AnotherWindow, self).__init__()
        self.resize(400, 300)
        self.setWindowTitle("this is another window")