Tutorial on PyQt6 QLineEdit

QLineEdit is a widget in PyQt6 used for single-line text input.

It supports basic text handling, placeholder text, input masks, and advanced features like password fields, text validation, and signals for interactive applications.

In this tutorial, we’ll cover:

1. Basics of QLineEdit

QLineEdit is a simple single-line text box for user input. You can set and retrieve text using the setText() and text() methods.

Example: Basic QLineEdit Setup

from PyQt6.QtWidgets import QApplication, QLineEdit, QMainWindow

def main():
    app = QApplication([])
    window = QMainWindow()
    window.setWindowTitle("Basic QLineEdit Example")
    window.setGeometry(100, 100, 300, 200)

    line_edit = QLineEdit(window)
    line_edit.setGeometry(50, 50, 200, 30)
    line_edit.setText("Hello, PyQt6!")

    window.show()
    app.exec()

if __name__ == "__main__":
    main()

Output:

• A window with a QLineEdit pre-filled with “Hello, PyQt6!”.

2. Adding Placeholder Text

Placeholder text is a hint shown in the QLineEdit when it is empty.

Example: Adding Placeholder Text

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 200, 30)
line_edit.setPlaceholderText("Enter your text here...")

Output:

• A text box with a placeholder saying “Enter your text here…” until the user types something.

3. Handling Input with Signals

QLineEdit provides signals like textChanged, returnPressed, and editingFinished to handle user interactions.

Example: Handling Text Changes

from PyQt6.QtWidgets import QApplication, QLineEdit, QMainWindow
from PyQt6.QtCore import Qt

def on_text_change(text):
    print(f"Text changed: {text}")

def main():
    app = QApplication([])
    window = QMainWindow()
    window.setWindowTitle("Text Change Example")
    window.setGeometry(100, 100, 300, 200)

    line_edit = QLineEdit(window)
    line_edit.setGeometry(50, 50, 200, 30)
    line_edit.textChanged.connect(on_text_change)

    window.show()
    app.exec()

if __name__ == "__main__":
    main()

Output:

• Prints the text to the console as the user types.

Example: Handling Return Key Press

def on_return_pressed():
    print("Return key pressed!")

line_edit.returnPressed.connect(on_return_pressed)

4. Password Fields

You can mask input in a QLineEdit to create a password field.

Example: Password Field

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 200, 30)
line_edit.setEchoMode(QLineEdit.EchoMode.Password)

Output:

• Text input will be replaced by dots or asterisks, depending on the system style.

5. Text Validation

QLineEdit allows you to validate input using regular expressions or custom validators.

Example: Numeric Validation

from PyQt6.QtWidgets import QLineEdit, QMainWindow, QApplication
from PyQt6.QtGui import QIntValidator

def main():
    app = QApplication([])
    window = QMainWindow()
    window.setWindowTitle("Numeric Validation Example")
    window.setGeometry(100, 100, 300, 200)

    line_edit = QLineEdit(window)
    line_edit.setGeometry(50, 50, 200, 30)
    line_edit.setValidator(QIntValidator(0, 100))  # Accepts integers from 0 to 100

    window.show()
    app.exec()

if __name__ == "__main__":
    main()

Output:

• The text box accepts only integers between 0 and 100.

Example: Custom Regular Expression Validation

from PyQt6.QtGui import QRegularExpressionValidator
from PyQt6.QtCore import QRegularExpression

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 200, 30)
regex = QRegularExpression("[a-zA-Z]{5,10}")  # Accepts 5-10 alphabetic characters
line_edit.setValidator(QRegularExpressionValidator(regex))

6. Using Input Masks

Input masks enforce a specific input format.

Example: Date Input Mask

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 200, 30)
line_edit.setInputMask("0000-00-00")  # Enforces YYYY-MM-DD format

Output:

• The text box accepts input in the format YYYY-MM-DD.

7. Styling QLineEdit

You can customize the appearance of QLineEdit using setStyleSheet().

Example: Styling QLineEdit

line_edit.setStyleSheet("""
    QLineEdit {
        background-color: lightyellow;
        border: 2px solid blue;
        border-radius: 5px;
        font-size: 16px;
    }
    QLineEdit:focus {
        border-color: green;
    }
""")

8. Practical Examples

Example 1: Search Box with a Button

from PyQt6.QtWidgets import QApplication, QMainWindow, QLineEdit, QPushButton

def on_search():
    text = line_edit.text()
    print(f"Searching for: {text}")

app = QApplication([])
window = QMainWindow()
window.setWindowTitle("Search Box Example")
window.setGeometry(100, 100, 300, 200)

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 150, 30)
line_edit.setPlaceholderText("Enter search term...")

button = QPushButton("Search", window)
button.setGeometry(210, 50, 70, 30)
button.clicked.connect(on_search)

window.show()
app.exec()

Output:

• Clicking “Search” prints the entered text to the console.

Example 2: Dynamic Character Counter

from PyQt6.QtWidgets import QApplication, QMainWindow, QLineEdit, QLabel

def update_character_count():
    count = len(line_edit.text())
    label.setText(f"Characters: {count}")

app = QApplication([])
window = QMainWindow()
window.setWindowTitle("Character Counter Example")
window.setGeometry(100, 100, 300, 200)

line_edit = QLineEdit(window)
line_edit.setGeometry(50, 50, 200, 30)
line_edit.textChanged.connect(update_character_count)

label = QLabel("Characters: 0", window)
label.setGeometry(50, 90, 200, 30)

window.show()
app.exec()

Output:

• Displays the number of characters typed in real-time.

Example 3: Login Form

from PyQt6.QtWidgets import QApplication, QMainWindow, QLineEdit, QPushButton, QLabel

def on_login():
    username = username_edit.text()
    password = password_edit.text()
    if username == "admin" and password == "password":
        label.setText("Login Successful!")
    else:
        label.setText("Invalid Credentials")

app = QApplication([])
window = QMainWindow()
window.setWindowTitle("Login Form")
window.setGeometry(100, 100, 300, 200)

username_edit = QLineEdit(window)
username_edit.setGeometry(50, 50, 200, 30)
username_edit.setPlaceholderText("Username")

password_edit = QLineEdit(window)
password_edit.setGeometry(50, 90, 200, 30)
password_edit.setPlaceholderText("Password")
password_edit.setEchoMode(QLineEdit.EchoMode.Password)

button = QPushButton("Login", window)
button.setGeometry(100, 130, 100, 30)
button.clicked.connect(on_login)

label = QLabel("", window)
label.setGeometry(50, 170, 200, 30)

window.show()
app.exec()

Output:

• A login form with validation.

Summary

In this tutorial, we covered:

1. Basics of QLineEdit: Creating text input boxes and setting text.
2. Placeholder Text: Adding hints for users.
3. Signals: Handling events like textChanged and returnPressed.
4. Password Fields: Masking input for sensitive data.
5. Text Validation: Enforcing specific formats with validators.
6. Input Masks: Restricting input to predefined patterns.
7. Styling: Customizing appearance with CSS.
8. Practical Examples: Building search boxes, character counters, and login forms.

QLineEdit is a versatile widget that plays a key role in interactive PyQt6 applications, enabling robust user input handling.