from PyQt5.QtWidgets import QTextEdit, QApplication,QListWidget, QWidget, QPushButton, QToolTip, QMessageBox, QLineEdit, QLabel, QGridLayout, QInputDialog
from PyQt5.QtGui import QFont
from PyQt5.QtCore import QCoreApplication
from PyQt5 import QtCore, QtGui, QtWidgets
import time
class Window(QtWidgets.QMainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.setupUi(self)
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(574, 311)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.returnt = QtWidgets.QLineEdit(self.centralwidget)
        self.returnt.setGeometry(QtCore.QRect(180, 110, 171, 41))
        self.returnt.setObjectName("returnt")
        self.beg = QtWidgets.QPushButton(self.centralwidget)
        self.beg.setGeometry(QtCore.QRect(410, 210, 75, 23))
        self.beg.setObjectName("beg")
        self.beg.clicked.connect(self.buttonClicked)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 574, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.beg.setText(_translate("MainWindow", "Начать"))
    def buttonClicked(self):
        for i in range(5):
            self.returnt.setText(str(i))
            time.sleep(1)
            
app = QtWidgets.QApplication(sys.argv)
ex = Window()
ex.show()
sys.exit(app.exec_())

     def buttonClicked(self):
        for i in range(5):
            self.returnt.setText(str(i))
            time.sleep(1)
            self.returnt.repaint()