How to communicate or switch between two windows in PyQt?

Question

I am developing an application using python and Qt.

I have designed 2 Main windows ie..QMainWindow (Not QWidget or QDialog) using Qt.

Let it be.

1.

Answer 1

to match username and password.

import sys
from PyQt5 import QtGui, QtCore, QtWidgets
from PyQt5.QtWidgets import QApplication, QDialog, QDialogButtonBox, QFormLayout, QLabel, QLineEdit, QWidget, QVBoxLayout, QMessageBox

class LoginDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super(LoginDialog, self).__init__(parent)

        self.username = QLineEdit()
        self.password = QLineEdit()
        loginLayout = QFormLayout()
        loginLayout.addRow("Username", self.username)
        loginLayout.addRow("Password", self.password)

        self.buttons = QDialogButtonBox(QDialogButtonBox.Ok | QDialogButtonBox.Cancel)
        self.buttons.accepted.connect(self.check)
        self.buttons.rejected.connect(self.reject)

        layout = QVBoxLayout()
        layout.addLayout(loginLayout)
        layout.addWidget(self.buttons)
        self.setLayout(layout)

    def check(self):
        if str(self.username.text()) == "foo" and str(self.password.text()) == "bar": # do actual login check
            self.accept()
        else:
            QMessageBox.warning(
                self, 'Error', 'Bad user or password')
            pass # or inform the user about bad username/password

    def my_exception_hook(exctype, value, traceback):
        # Print the error and traceback
        print(exctype, value, traceback)
        # Call the normal Exception hook after
        sys._excepthook(exctype, value, traceback)
        sys.exit(1)

    # Back up the reference to the exceptionhook
    sys._excepthook = sys.excepthook

    # Set the exception hook to our wrapping function
    sys.excepthook = my_exception_hook


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)

        self.label = QLabel()
        self.setCentralWidget(self.label)

    def setUsername(self, username):
        # do whatever you want with the username
        self.username = username
        self.label.setText("%s%s%s" % ("Username entered: ", self.username, "\npassword ok!"))


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

    login = LoginDialog()
    if not login.exec_(): # 'reject': user pressed 'Cancel', so quit
        sys.exit(-1)      # instead of -1 another action can be triggered here.     

    # 'accept': continue
    main = MainWindow()

    # get the username, and supply it to main window
    main.setUsername(login.username.text())
    main.show()

    sys.exit(app.exec_())