Python login form with PyQt - User authentication

Last update on April 25 2025 12:52:02 (UTC/GMT +8 hours)

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:

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