如何从现有窗口创建新的PyQt4窗口？

问题描述：

我一直在尝试使用python3和Qt4从现有窗口调用新窗口。

我已经使用Qt Designer创建了两个窗口（主应用程序和另一个），并将Qt Designer生成的.ui文件转换为.py脚本-
但我似乎无法从主应用程序创建新窗口。

我尝试这样做：

############### MAIN APPLICATION SCRIPT ################

from PyQt4 import QtCore, QtGui
import v2

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(194, 101)
        self.button1 = QtGui.QPushButton(Form)
        self.button1.setGeometry(QtCore.QRect(50, 30, 99, 23))
        self.button1.setObjectName(_fromUtf8("button1"))

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(QtGui.QApplication.translate("Form", "Form", None, QtGui.QApplication.UnicodeUTF8))
        self.button1.setText(QtGui.QApplication.translate("Form", "Ventana", None, QtGui.QApplication.UnicodeUTF8))

        self.button1.connect(self.button1, QtCore.SIGNAL(_fromUtf8("clicked()")), self.mbutton1)

    def mbutton1(self):
        v2.main()



if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Form = QtGui.QWidget()
    ui = Ui_Form()
    ui.setupUi(Form)
    Form.show()
    sys.exit(app.exec_())



################## SECOND WINDOW #######################

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(400, 300)
        self.label = QtGui.QLabel(Form)
        self.label.setGeometry(QtCore.QRect(160, 40, 57, 14))
        self.label.setObjectName(_fromUtf8("label"))

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(QtGui.QApplication.translate("Form", "Form", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("Form", "LABEL 2", None, QtGui.QApplication.UnicodeUTF8))

def main():
    import sys
    app = QtGui.QApplication(sys.argv)
    Form = QtGui.QWidget()
    ui = Ui_Form()
    ui.setupUi(Form)
    Form.show()
    sys.exit(app.exec_())

但我收到此错误消息：

 QCoreApplication::exec: The event loop is already running
 QPixmap: Must construct a QApplication before a QPaintDevice

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