Qt输入控件为空时，程序自动退出，怎么解决

Question

如图所示简易计算器，当没有输入是点击就算会导致程序报错退出，如何实现当数据输入错误无法正常运算是程序保持运行。

主程序如下：

import sys

import math
iPI = 3.1415926535898/180.0
PI = 3.1415926535898
from PyQt5 import QtWidgets
from ttt import Ui_MainWindow
from PyQt5 import QtCore

class My_MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super(My_MainWindow, self).__init__(parent)       # 初始化
        self.setupUi(self)

        self.pushButton.clicked.connect(self.count)       # 调用count函数
        self.pushButton_2.clicked.connect(self.close)     # 关闭窗口


    def count(self):

        a = float(self.lineEdit.text())
        b = float(self.lineEdit_2.text())
        c = a + b
        self.lineEdit_3.setText(str(c))


if __name__ == '__main__':
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling)  # 屏幕自适应
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = My_MainWindow()
    MainWindow.show()
    sys.exit(app.exec_())

窗口代码：

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'ttt.ui'
#
# Created by: PyQt5 UI code generator 5.15.9
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(448, 238)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.widget = QtWidgets.QWidget(self.centralwidget)
        self.widget.setGeometry(QtCore.QRect(50, 70, 331, 102))
        self.widget.setObjectName("widget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.widget)
        self.verticalLayout.setContentsMargins(0, 0, 0, 0)
        self.verticalLayout.setObjectName("verticalLayout")
        self.horizontalLayout = QtWidgets.QHBoxLayout()
        self.horizontalLayout.setObjectName("horizontalLayout")
        spacerItem = QtWidgets.QSpacerItem(40, 20, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Minimum)
        self.horizontalLayout.addItem(spacerItem)
        self.lineEdit = QtWidgets.QLineEdit(self.widget)
        font = QtGui.QFont()
        font.setPointSize(20)
        self.lineEdit.setFont(font)
        self.lineEdit.setAlignment(QtCore.Qt.AlignCenter)
        self.lineEdit.setObjectName("lineEdit")
        self.horizontalLayout.addWidget(self.lineEdit)
        self.comboBox = QtWidgets.QComboBox(self.widget)
        font = QtGui.QFont()
        font.setPointSize(20)
        self.comboBox.setFont(font)
        self.comboBox.setObjectName("comboBox")
        self.comboBox.addItem("")
        self.comboBox.addItem("")
        self.comboBox.addItem("")
        self.comboBox.addItem("")
        self.horizontalLayout.addWidget(self.comboBox)
        self.lineEdit_2 = QtWidgets.QLineEdit(self.widget)
        font = QtGui.QFont()
        font.setPointSize(20)
        self.lineEdit_2.setFont(font)
        self.lineEdit_2.setAlignment(QtCore.Qt.AlignCenter)
        self.lineEdit_2.setObjectName("lineEdit_2")
        self.horizontalLayout.addWidget(self.lineEdit_2)
        self.label = QtWidgets.QLabel(self.widget)
        font = QtGui.QFont()
        font.setPointSize(20)
        font.setBold(True)
        font.setWeight(75)
        self.label.setFont(font)
        self.label.setAlignment(QtCore.Qt.AlignCenter)
        self.label.setObjectName("label")
        self.horizontalLayout.addWidget(self.label)
        self.lineEdit_3 = QtWidgets.QLineEdit(self.widget)
        font = QtGui.QFont()
        font.setPointSize(20)
        self.lineEdit_3.setFont(font)
        self.lineEdit_3.setAlignment(QtCore.Qt.AlignCenter)
        self.lineEdit_3.setObjectName("lineEdit_3")
        self.horizontalLayout.addWidget(self.lineEdit_3)
        spacerItem1 = QtWidgets.QSpacerItem(40, 20, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Minimum)
        self.horizontalLayout.addItem(spacerItem1)
        self.verticalLayout.addLayout(self.horizontalLayout)
        spacerItem2 = QtWidgets.QSpacerItem(20, 40, QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.Expanding)
        self.verticalLayout.addItem(spacerItem2)
        self.horizontalLayout_2 = QtWidgets.QHBoxLayout()
        self.horizontalLayout_2.setObjectName("horizontalLayout_2")
        spacerItem3 = QtWidgets.QSpacerItem(40, 20, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Minimum)
        self.horizontalLayout_2.addItem(spacerItem3)
        self.pushButton = QtWidgets.QPushButton(self.widget)
        font = QtGui.QFont()
        font.setPointSize(16)
        font.setBold(True)
        font.setWeight(75)
        self.pushButton.setFont(font)
        self.pushButton.setObjectName("pushButton")
        self.horizontalLayout_2.addWidget(self.pushButton)
        spacerItem4 = QtWidgets.QSpacerItem(40, 20, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Minimum)
        self.horizontalLayout_2.addItem(spacerItem4)
        self.pushButton_2 = QtWidgets.QPushButton(self.widget)
        font = QtGui.QFont()
        font.setPointSize(16)
        font.setBold(True)
        font.setWeight(75)
        self.pushButton_2.setFont(font)
        self.pushButton_2.setObjectName("pushButton_2")
        self.horizontalLayout_2.addWidget(self.pushButton_2)
        spacerItem5 = QtWidgets.QSpacerItem(40, 20, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Minimum)
        self.horizontalLayout_2.addItem(spacerItem5)
        self.verticalLayout.addLayout(self.horizontalLayout_2)
        MainWindow.setCentralWidget(self.centralwidget)

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.comboBox.setItemText(0, _translate("MainWindow", "+"))
        self.comboBox.setItemText(1, _translate("MainWindow", "-"))
        self.comboBox.setItemText(2, _translate("MainWindow", "×"))
        self.comboBox.setItemText(3, _translate("MainWindow", "÷"))
        self.label.setText(_translate("MainWindow", "="))
        self.pushButton.setText(_translate("MainWindow", "计  算"))
        self.pushButton_2.setText(_translate("MainWindow", "退  出"))

Answer 1

输入为空，在计算时，转为float类型会报错。
在计算时捕获异常，并给出提示。

    def count(self):
        try:
            a = float(self.lineEdit.text())
            b = float(self.lineEdit_2.text())
            c = a + b
            self.lineEdit_3.setText(str(c))
        except ValueError:
            QMessageBox.warning(self, "错误", "输入无效")