How to check login and password?

Question

MySQL

I have different variations:

for row in logs:
                if row == login:
                    for row in passs:
                        if row == passw:
                              self.exampleApp.show()
                              break
                        elif row != passw:
                              self.errorapp.show()
                              break
                elif row != login:
                    self.errorapp.show()
                    break

for row in logs:
                if row == login:
                    for row in passs:
                        if row == passw:
                            self.exampleApp.show()
                            break
                        else:
                            self.errorapp.show()
                            break
                    else:
                        self.errorapp.show()
                        break
                else:
                    self.errorapp.show()
                    break

for row in logs:
                if row == login:
                    for row in passs:
                        if row == passw:
                            try:
                                self.exampleApp.show()
                            except:
                                self.errorapp.show()

I'll never know what's wrong, but if I get into both the login and the password, then I immediately get 2 windows - and which is needed, and a dialog box with an error. Please tell me below is the code of the whole window

import sys
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QInputDialog, QLineEdit, QDialog
import pymysql.cursors
from main1open import Windowone
from main2open import Windowtwo
from ruinedopen import Windowthree
import mysql.connector
from mysql.connector import MySQLConnection, Error
connection = pymysql.connect(host='127.0.0.1',
                             user='root',
                             password='adminadmin',
                             db='mydb',
                             charset='utf8mb4',)
print("connected!!!")

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(400, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(130, 360, 131, 41))
        self.pushButton.setObjectName("pushButton")
        self.pushButton_2 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton_2.setGeometry(QtCore.QRect(130, 410, 131, 41))
        self.pushButton_2.setObjectName("pushButton_2")
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setGeometry(QtCore.QRect(50, 179, 281, 31))
        self.lineEdit.setObjectName("lineEdit")
        self.lineEdit_2 = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit_2.setGeometry(QtCore.QRect(50, 260, 281, 31))
        self.lineEdit_2.setObjectName("lineEdit_2")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(50, 230, 111, 31))
        font = QtGui.QFont()
        font.setPointSize(14)
        font.setBold(True)
        font.setItalic(True)
        font.setWeight(75)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(50, 150, 91, 31))
        font = QtGui.QFont()
        font.setPointSize(14)
        font.setBold(True)
        font.setItalic(True)
        font.setWeight(75)
        self.label_2.setFont(font)
        self.label_2.setObjectName("label_2")
        MainWindow.setCentralWidget(self.centralwidget)
        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", "log in"))
        self.pushButton_2.setText(_translate("MainWindow", "create an account"))
        self.label.setText(_translate("MainWindow", "password"))
        self.label_2.setText(_translate("MainWindow", "Login"))



class ExampleApp(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.pushButton.clicked.connect(self.onClicked)
        self.pushButton_2.clicked.connect(self.onClicked1)

        self.exampleApp = Windowone()
        self.errorapp = Windowthree()
        self.exampleApp_2 = Windowtwo()

    def onClicked(self):
        with connection:
            curs = connection.cursor()

            curs.execute("SELECT username FROM клиент")
            logs = curs.fetchall()# выполнение запроса
            login = (self.lineEdit.text(),)

            curs.execute("SELECT password FROM клиент WHERE username = %s ", login[0])
            passs = curs.fetchall()
            passw = (self.lineEdit_2.text(), )
            for row in logs:
                if row == login:
                    for row in passs:
                        if row == passw:
                            try:
                                self.exampleApp.show()
                            except:
                                self.errorapp.show()



    def onClicked1(self):
        self.exampleApp_2.show()

class errorapp(QDialog,ExampleApp):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.pushButton.clicked.connect(self.onClicked)
        self.errorapp = Windowthree()

if __name__=="__main__":
    app = QtWidgets.QApplication(sys.argv)
    window = ExampleApp()
    window.show()
    sys.exit(app.exec_())

Answer 1

You don’t stop cycles with a check anywhere.
Instead of break - return, write