Make desktop application with Python part 2

Hi Pythonistas!

This is part 2 of the series “Make Desktop Application with Python”.In this post, we will learn how to take input from the user, validate the input and bind an action with a function. Let us jump into the code. If you need the basics for PyQt please click here

Code

import sys
import re
from PyQt5.QtWidgets import QApplication, QWidget, QLineEdit, QPushButton, QMessageBox
from PyQt5.QtGui import QRegExpValidator, QValidator
from PyQt5.QtCore import QRegExp


def main():
    app = QApplication(sys.argv)
    window = QWidget()
    window.setWindowTitle('Part 2 App')

    input_field = QLineEdit(window)
    input_field.move(100, 50)
    # Set the validator for the input field
    validator = QRegExpValidator(QRegExp('.*[a-zA-Z]+.*'), input_field)
    input_field.setValidator(validator)

    button = QPushButton('Click Me!', window)
    button.move(100, 100)

    def on_button_clicked():
         input_text = input_field.text()
         validation_state = validator.validate(input_text, 0)[0]
         if validation_state == QValidator.Acceptable:
                 QMessageBox.information(window, 'Alert', f'Button was clicked with input "{input_text}"!')
         else:
                 QMessageBox.warning(window, 'Error', 'Invalid input!')

    button.clicked.connect(on_button_clicked)
    window.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Add Textbox in window

input_field = QLineEdit(window)

This we add a text input in the main window. Users can input text in this field

Adding validation to input field

validator = QRegExpValidator(QRegExp('.*[a-zA-Z]+.*'), input_field)
input_field.setValidator(validator)

Here we add regex as per our requirement. Here we use at least one alphabet.

Adding push button 

button = QPushButton('Click Me!', window)

This will add a push button with the label click me

Defining action for button click

def on_button_clicked():
    input_text = input_field.text()
    validation_state = validator.validate(input_text, 0)[0]
    if validation_state == QValidator.Acceptable:
        QMessageBox.information(window, 'Alert', f'Button was clicked with input "{input_text}"!')
    else:
        QMessageBox.warning(window, 'Error', 'Invalid input!')

Read text from input box

input_field.text()

Validate the text against our validator

validation_state = validator.validate(input_text, 0)[0]

Validating the user’s input with our validation. Result of validation we 0, 1 or 2

0 - Invalid

1 - Intermediate

2- Acceptable

Showing alert to user

QMessageBox.information(window, 'Alert', f'Button was clicked with input "{input_text}"!')

This will show information message to users

QMessageBox.warning(window, 'Error', 'Invalid input!')

This shows a warning message to the user

Binding the button click to the function

button.clicked.connect(on_button_clicked)

Here the button click is binded to the function on_button_clicked. This function will call when we click on the button

Output

Success Alert

Warning Alert

I hope you have learned something from this post. In the next post we will make a complete desktop application with Python. Please share your suggestions with afsal@parseltongue.co.in