Python login form with PyQt - User authentication

Python PyQt Widgets: Exercise-9 with Solution

Write a Python program to create a login form that accepts username and password and validates them. Use the PyQt5 module.

From doc.qt.io:

QApplication Class: The QApplication class manages the GUI application's control flow and main settings.

QMainWindow Class: The QMainWindow class provides a main application window.

QWidget Class: The QWidget class is the base class of all user interface objects

QFormLayout Class: The QFormLayout class manages forms of input widgets and their associated labels

QLabel Class: The QLabel widget provides a text or image display.

QLineEdit Class: The QLineEdit widget is a one-line text editor.

QPushButton Class: The QPushButton widget provides a command button.

QMessageBox Class: The QMessageBox class provides a modal dialog for informing the user or for asking the user a question and receiving an answer.

Sample Solution:

Python Code:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QFormLayout, QLabel, QLineEdit, QPushButton, QMessageBox

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

        # Set the window properties (title and initial size)
        self.setWindowTitle("Login Form")
        self.setGeometry(100, 100, 300, 150)  # (x, y, width, height)

        # Create a central widget for the main window
        central_widget = QWidget()
        self.setCentralWidget(central_widget)

        # Create a QFormLayout to arrange the widgets
        form_layout = QFormLayout()

        # Create QLabel and QLineEdit widgets for username
        username_label = QLabel("Username:")
        self.username_field = QLineEdit()

        # Create QLabel and QLineEdit widgets for password
        password_label = QLabel("Password:")
        self.password_field = QLineEdit()
        self.password_field.setEchoMode(QLineEdit.Password)

        # Create a QPushButton for login
        login_button = QPushButton("Login")
        login_button.clicked.connect(self.login)

        # Add widgets to the form layout
        form_layout.addRow(username_label, self.username_field)
        form_layout.addRow(password_label, self.password_field)
        form_layout.addRow(login_button)

        # Set the layout for the central widget
        central_widget.setLayout(form_layout)

    def login(self):
        # Retrieve the username and password entered by the user
        username = self.username_field.text()
        password = self.password_field.text()

        # Check if the username and password are valid (for demonstration purposes)
        if username == "admin" and password == "pass123$":
            QMessageBox.information(self, "Login Successful", "Welcome, " + username + "!")
        else:
            QMessageBox.warning(self, "Login Failed", "Invalid username or password. Please try again.")

def main():
    app = QApplication(sys.argv)
    window = LoginFormApp()
    window.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Explanation:

In the exercise above -

• Import the necessary modules.
• Create a "QMainWindow" named "LoginFormApp" with a central widget.
• Set the window's title and initial size.
• Create a "QFormLayout" named form_layout to arrange the widgets neatly.
• Create a 'QLabel' and 'QLineEdit' widgets for username and password input fields. We also created a "QPushButton" for login.
• The password field is set to echo mode QLineEdit.Password to hide a password.
• Connect the login method to the "Login" button's click event, which handles the login process.
• In the login method, we retrieve the user's username and password and validate them. For demonstration purposes, we use hardcoded credentials.
• If the credentials are valid, a success message is displayed using 'QMessageBox.information'. Otherwise, an error message is displayed using 'QMessageBox.warning'.
• In the main function, we create the PyQt application, create an instance of the "LoginFormApp" class, show the window, and run the application's event loop.

Output:

Flowchart:

Python Code Editor:

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