class Base(QtWidgets.QWidget):
    def __init__(self):
        super(Base, self).__init__()
        self.startUW()
    def startUW(self):
        self.vbox = QtWidgets.QVBoxLayout()
        self.checkboxItem()
        self.vbox.addStretch(1)
        button = QtWidgets.QPushButton("Show", self)
        button.clicked.connect(self.showItem)
        self.lab = QtWidgets.QLabel("Выберите Пункт", self)
  
        self.vbox.addWidget(button, 3)
        self.vbox.addWidget(self.lab, 4)
        self.setWindowTitle("My_first_programm")
        self.setWindowIcon(QtGui.QIcon('pythonlogo.png'))
        self.setGeometry(50, 50, 1000, 600)
        self.center()
        self.setLayout(self.vbox)
        self.show()