как сделать вывод из tableWidget в excel с типами данных

Предположим, что первая колонка у вас содержит какие-то целые числа.

Тогда

            ...
            if col == 0:
                df.at[row, columnHeaders[col]] = int(item.text()) \
                    if item is not None and item.text() else 0
            ...

import sys
import pandas as pd 

from PyQt5.QtWidgets import QApplication, QMainWindow, \
    QStackedWidget, QMessageBox, QFileDialog
from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_dialog(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(221, 160)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(50, 90, 121, 23))
        self.pushButton.setObjectName("pushButton")
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setGeometry(QtCore.QRect(50, 50, 121, 20))
        self.lineEdit.setObjectName("lineEdit")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(50, 20, 121, 16))
        self.label.setObjectName("label")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 221, 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.pushButton.setText(_translate("MainWindow", "ОК"))
        self.label.setText(_translate("MainWindow", "Введите номер строки"))
        


class Ui_table(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(1000, 684)
        MainWindow.setMinimumSize(QtCore.QSize(1000, 684))
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(15, 350, 131, 31))
        self.pushButton.setObjectName("pushButton")
        self.tableWidget = QtWidgets.QTableWidget(self.centralwidget)
        self.tableWidget.setGeometry(QtCore.QRect(170, 10, 811, 631))
        self.tableWidget.setObjectName("tableWidget")
        self.tableWidget.setColumnCount(0)
        self.tableWidget.setRowCount(0)
        self.pushButton_2 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_2.setGeometry(QtCore.QRect(15, 50, 131, 31))
        self.pushButton_2.setObjectName("pushButton_2")
        self.pushButton_3 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_3.setGeometry(QtCore.QRect(15, 100, 131, 31))
        self.pushButton_3.setObjectName("pushButton_3")
        self.pushButton_4 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_4.setGeometry(QtCore.QRect(15, 150, 131, 31))
        self.pushButton_4.setObjectName("pushButton_4")
        self.pushButton_5 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_5.setGeometry(QtCore.QRect(15, 400, 131, 31))
        self.pushButton_5.setObjectName("pushButton_5")
        self.pushButton_6 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_6.setGeometry(QtCore.QRect(15, 600, 131, 31))
        self.pushButton_6.setObjectName("pushButton_6")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 1000, 21))
        self.menubar.setObjectName("menubar")
        self.menu = QtWidgets.QMenu(self.menubar)
        self.menu.setObjectName("menu")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.action = QtWidgets.QAction(MainWindow)
        self.action.setObjectName("action")
        self.menu.addAction(self.action)
        self.menubar.addAction(self.menu.menuAction())

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "обновить"))
        self.pushButton_2.setText(_translate("MainWindow", "добавить"))
        self.pushButton_3.setText(_translate("MainWindow", "удалить"))
        self.pushButton_4.setText(_translate("MainWindow", "сохранить"))
        self.pushButton_5.setText(_translate("MainWindow", "поиск"))
        self.pushButton_6.setText(_translate("MainWindow", "Выход"))
        self.menu.setTitle(_translate("MainWindow", "открыть"))
        self.action.setText(_translate("MainWindow", "открыть файл"))


class Dialog(QMainWindow, Ui_dialog):              
    def __init__(self, parent=None):
        super(Dialog, self).__init__(parent)
        self.setupUi(self) 
        
        self.setWindowFlags(QtCore.Qt.Window | QtCore.Qt.WindowStaysOnTopHint)


class StartMenuMain(QMainWindow, Ui_table):                          
    def __init__(self, parent=None):
        super(StartMenuMain, self).__init__(parent)
        self.setupUi(self) 
        
        self.fname = None                                                            
        self.initUI()
        
        self.dialog = Dialog()                                          
        self.dialog.pushButton.clicked.connect(self.searchOk)           
        
    def initUI(self):
        self.pushButton.clicked.connect(self.update)
        self.action.triggered.connect(self.open_file)
        self.pushButton_2.clicked.connect(self.addRow)                        
        self.pushButton_3.clicked.connect(self.delRow)                        
        self.pushButton_4.clicked.connect(self.exportToExcel) 
        self.pushButton_5.clicked.connect(self.search)
        self.pushButton_6.clicked.connect(self.exit)

        self.pushButton.setStyleSheet("color: white; background-color: #b6afa9;"
                                       "border-radius: 10px;")
        self.pushButton_2.setStyleSheet("color: white; background-color: #b6afa9;"
                                       "border-radius: 10px;")
        self.pushButton_3.setStyleSheet("color: white; background-color: #b6afa9;"
                                          "border-radius: 10px;")
        self.pushButton_4.setStyleSheet("color: white; background-color: #b6afa9;"
                                      "border-radius: 10px;")
        self.pushButton_5.setStyleSheet("color: white; background-color: #b6afa9;"
                                      "border-radius: 10px;")
        self.pushButton_6.setStyleSheet("color: white; background-color: #b6afa9;"
                                      "border-radius: 10px;")



    def exit(self):
        exit()

    def update(self):
        if not self.fname:                                                            
            QMessageBox.critical(self, 'Ошибка!', "Выберите Exсel файл")
            return                                                                  
        excel_file_path = self.fname
                     
        worksheet_name = 'Sheet1'   
        self.loadExcelData(excel_file_path, worksheet_name)

    def open_file(self):
        self.fname, _ = QtWidgets.QFileDialog.getOpenFileName(self, 'Выберите файл', '.',  
            "Файлы Exсel (*.xlsx)") 
        print(f'fname = {self.fname}')    
        
    def loadExcelData(self, excel_file_path, worksheet_name):
        df = pd.read_excel(excel_file_path, worksheet_name)
        if df.size == 0:
            return

        df.fillna('', inplace=True)
        self.tableWidget.setRowCount(df.shape[0])
        self.tableWidget.setColumnCount(df.shape[1])
        self.tableWidget.setHorizontalHeaderLabels(df.columns)

        
        for row in df.iterrows():
            values = row[1]
            for col_index, value in enumerate(values):
                if isinstance(value, (float, int)):
                    value = '{0:0,.0f}'.format(value)
                tableItem = QtWidgets.QTableWidgetItem(str(value))

                self.tableWidget.setItem(row[0], col_index, tableItem)
        self.tableWidget.setColumnWidth(2, 300)


    def search(self):
        if not self.fname:                                                            
            QMessageBox.critical(self, 'Ошибка!', "Выберите Exсel файл")
            return
        self.dialog.show()

    def searchOk(self):  

        row = self.dialog.lineEdit.text()
        _rows = self.tableWidget.rowCount()
        if not row.isdigit():
            msg = QMessageBox.information(self, 'Внимание', 'Укажите правильно строку.')
            self.dialog.hide()
            return
            
        if int(row) > _rows:
            msg = QMessageBox.information(self, 'Внимание', 'Укажите правильно строку.')
            self.dialog.hide()
            return        
        self.dialog.hide()
        
        cols = self.tableWidget.columnCount()      

        rows = int(row) -1                                                       
        

        stolb = ["Номер", "ФИО", "ЗП"]
        a = ""
        for i in range(cols):   
            item = self.tableWidget.item(int(rows), i)                
            if item:
                a = a + stolb[i] + " " + (self.tableWidget.item(int(rows), i).text()) + "\n"
            else:
                a = a + stolb[i] + " ? пусто ? \n"
        QMessageBox.information(self, 'Поиск', a)     

    def addRow(self):
        rowPosition = self.tableWidget.rowCount()
        if not rowPosition:
            msg = QMessageBox.information(self, 'Внимание', 'Выберите Exсel файл для добавления строки.')
            return     
        self.tableWidget.insertRow(rowPosition)

    def delRow(self):
        row = self.tableWidget.currentRow()
        if row == -1:
            msg = QMessageBox.information(self, 'Внимание', 'Выберите строку для удаления')
            return
        self.tableWidget.removeRow(row)


    def exportToExcel(self):
        rows = self.tableWidget.rowCount()
        if not rows:
            msg = QMessageBox.information(self, 'Внимание', 'Нечего сохранять.')
            return      

        if not self.fname:
            msg = QMessageBox.information(self, 'Внимание', 'Не указан файл для сохранения.')
            return

        columnHeaders = []
        
        for j in range(self.tableWidget.model().columnCount()):
            columnHeaders.append(self.tableWidget.horizontalHeaderItem(j).text())

        df = pd.DataFrame(columns=columnHeaders)

        
        for row in range(self.tableWidget.rowCount()):
            for col in range(self.tableWidget.columnCount()):
                item = self.tableWidget.item(row, col)
                if col == 0:
                    df.at[row, columnHeaders[col]] = int(item.text()) \
                        if item is not None and item.text() else 0
                else:
                    df.at[row, columnHeaders[col]] = item.text() if item is not None else ""
        df.to_excel(self.fname, index=False)
        msg = QMessageBox.information(self, 'Excel', 'Файл сохранен')        


if __name__ == '__main__': 
    app = QApplication(sys.argv)

    startmenu_window = StartMenuMain()
    windows = QStackedWidget()

    windows.addWidget(startmenu_window)  
    windows.setWindowTitle("Работа с файлами")
    windows.show()
    sys.exit(app.exec_())