import sys
from PyQt4 import QtGui
class Base(QtGui.QWidget):
    def __init__(self):
        super(Base, self).__init__()
        self.startUW()
    def startUW(self):
        self.vbox = QtGui.QVBoxLayout()
        self.checkboxItem()
        self.vbox.addStretch(1)
        button = QtGui.QPushButton("Show", self)
        button.clicked.connect(self.showItem)
        self.lab = QtGui.QLabel("Ничего не выбрано!", self)
  
        self.vbox.addWidget(button, 3)
        self.vbox.addWidget(self.lab, 4)
        self.setWindowTitle("Select Item Printer")
        self.setFixedSize(400, 400)
        self.setLayout(self.vbox)
        self.show()
    def checkboxItem(self):
        array = ["Пунтк 1", "Пункт 2", "Пункт 3", "Пункт 4"]
        self.check = []
        index = 0
        
        for item_name in array:
            self.check.append(QtGui.QCheckBox(item_name, self))
            self.vbox.addWidget(self.check[index], index)
            index += 1
    def showItem(self):
        lib = ""
        index = 0
        while index != 4:
            
            if self.check[index].isChecked():     
                lib = lib  + " " + self.check[index].text()
                index += 1
            else:
                index += 1
            self.lab.setText(lib)
        
def main():
    app = QtGui.QApplication(sys.argv)
    gui = Base()
    sys.exit(app.exec_())
if __name__ == "__main__":
    main()

     def showItem(self):
        values = [1,2,3,4]
        sum_of_values = 0
        index = 0
        while index != 4:
            if self.check[index].isChecked():     
                sum_of_values += values[index]
                index += 1
            else:
                index += 1
            self.lab.setText(str(sum_of_values))