from PyQt4.QtGui import *
from PyQt4.QtCore import *
import lb_window_ui, time
 
class mainClass(QWidget, lb_window_ui.Ui_mainform):
    def __init__(self):
        super(mainClass, self).__init__()
        self.setupUi(self)
        self.start_btn.clicked.connect(self.addingtext)
 
    def addingtext(self):
        time.sleep(1)
        text = 'Text_1'
        self.item_lw.addItem(text)
        time.sleep(1)
        text2 = 'Text_2'
        self.item_lw.addItem(text2)      
 
if __name__ == '__main__':
    app = QApplication([])
    w = mainClass()
    w.show()
    app.exec_()