How to properly link two windows in pyqt5?

Question

Python

Goodnight. I don’t understand at all how to implement this on pyqt5:
There is an initial code:
Main window

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

# Form implementation generated from reading ui file './main_gui.ui'
#
# Created by: PyQt5 UI code generator 5.10.1
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(680, 0, 121, 51))
        self.label.setBaseSize(QtCore.QSize(4, 5))
        self.label.setStyleSheet("font: 24pt \".SF NS Text\";")
        self.label.setObjectName("label")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(330, 230, 113, 32))
        self.pushButton.setObjectName("pushButton")
        self.pushButton_2 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_2.setGeometry(QtCore.QRect(0, 0, 113, 32))
        self.pushButton_2.setObjectName("pushButton_2")
        self.pushButton_3 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_3.setGeometry(QtCore.QRect(330, 270, 113, 32))
        self.pushButton_3.setObjectName("pushButton_3")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 22))
        self.menubar.setObjectName("menubar")
        self.menuFile = QtWidgets.QMenu(self.menubar)
        self.menuFile.setObjectName("menuFile")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.toolBar = QtWidgets.QToolBar(MainWindow)
        self.toolBar.setObjectName("toolBar")
        MainWindow.addToolBar(QtCore.Qt.TopToolBarArea, self.toolBar)
        self.actionOpen = QtWidgets.QAction(MainWindow)
        self.actionOpen.setObjectName("actionOpen")
        self.actionOpen_2 = QtWidgets.QAction(MainWindow)
        self.actionOpen_2.setObjectName("actionOpen_2")
        self.menuFile.addAction(self.actionOpen_2)
        self.menubar.addAction(self.menuFile.menuAction())

        self.retranslateUi(MainWindow)
        self.pushButton_2.clicked.connect(MainWindow.close)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "Twitter"))
        self.pushButton.setText(_translate("MainWindow", "Start"))
        self.pushButton_2.setText(_translate("MainWindow", "Quit"))
        self.pushButton_3.setText(_translate("MainWindow", "Open CSV"))
        self.menuFile.setTitle(_translate("MainWindow", "File"))
        self.toolBar.setWindowTitle(_translate("MainWindow", "toolBar"))
        self.actionOpen.setText(_translate("MainWindow", "Open"))
        self.actionOpen_2.setText(_translate("MainWindow", "Open"))

Adding an event to a button

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QCalendarWidget, QFontDialog, QColorDialog, QTextEdit, QFileDialog, QTableWidgetItem, QTableWidget, QMainWindow

import sys
import os
import csv

from Desktop.main_gui import Ui_MainWindow
from Twitter.twitter import AppTwitter


class GuiTwitter(Ui_MainWindow):
    def main(self):
        self.pushButton.clicked.connect(AppTwitter)

        self.pushButton_3.clicked.connect(Sheet)


class MyTable(QTableWidget):
    def open_sheet(self):
        path = QFileDialog.getOpenFileName(self, 'Open CSV', os.getenv('Diplom'), 'CSV(*.csv)')
        if path[0] != '':
            with open(path[0], newline='', encoding='UTF-8') as csv_file:
                self.setRowCount(0)
                self.setColumnCount(30)
                my_file = csv.reader(csv_file, delimiter=',', quotechar='|')
                for row_data in my_file:
                    row = self.rowCount()
                    self.insertRow(row)
                    if len(row_data) > 30:
                        self.setColumnCount(len(row_data))
                    for column, stuff in enumerate(row_data):
                        item = QTableWidgetItem(stuff)
                        self.setItem(row, column, item)


class Sheet(QMainWindow):
    def __init__(self):
        super().__init__()

        self.form_widget = MyTable(30, 30)
        self.setCentralWidget(self.form_widget)

        self.form_widget.open_sheet()

        self.show()


if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = GuiTwitter()
    ui.setupUi(MainWindow)
    ui.main()
    MainWindow.show()
    sys.exit(app.exec_())

Actually here I have a question.
The GuiTwitter class originally only contained a pushButton click (not + pushButton_3).
The MyTable / Sheet class is used to open a system window and correctly display csv files.
Actually with them and the problem. I don't understand how to implement
Launched the program, main window, clicked on Open CSV - Selected file - Displayed CSV table. Here the table is not displayed. I understand that it is inserted incorrectly, because of this I ask for help.
She was originally taken from here https://www.youtube.com/watch?v=OZyhORYfZ1o

Answer 1

def getfiles(self):
        global fname
        fname = QFileDialog.getOpenFileName(self, "Open PNG", f"{cwd}/", "PNG (*.png);;GIF (*.gif);;JPG (*.jpg *.jpe *.JPEG );;TIFF (*.tiff);;All (*)")[0]
        if fname == '':
            QFileDialog(self, quit())
        with open(fname, 'rb') as data:
            self.ui.mylabel_2.setScaledContents(True)
            self.ui.mylabel.setText(f"Файл: {fname}")
            self.ui.mylabel_2.setPixmap(QtGui.QPixmap(f"{fname}"))

And so (the third line) is completely displayed.
cwd is a path variable.
For example like this:
cwd = os.path.expanduser('~')