Mastering PyQt5 QLabel: A Comprehensive Guide
The QLabel widget is a cornerstone of PyQt5 GUI development, offering a simple yet versatile way to display text and images. This tutorial delves into its functionalities, providing practical examples and best practices to elevate your PyQt5 skills.
Table of Contents
- Creating and Displaying QLabel Widgets
- Styling Text: Fonts, Colors, and HTML
- Precise Text Alignment
- Displaying Images with QLabel
- Word Wrapping and Text Size Adjustment
- Advanced Techniques: Signals and Slots
1. Creating and Displaying QLabel Widgets
Let’s begin by creating a basic QLabel to display text. This involves instantiating the QLabel class and setting its parent widget.
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget
app = QApplication(sys.argv)
window = QWidget()
label = QLabel("Hello, PyQt5!", window)
label.show()
window.show()
sys.exit(app.exec_())
This code snippet creates a simple window with the text “Hello, PyQt5!” displayed. The QLabel is a child of the QWidget, ensuring proper display within the window.
2. Styling Text: Fonts, Colors, and HTML
Beyond simple text display, you can customize QLabel’s appearance significantly. Let’s explore font styling, color changes, and the use of HTML for rich text formatting.
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget
from PyQt5.QtGui import QFont, QColor
app = QApplication(sys.argv)
window = QWidget()
label = QLabel("Hello, PyQt5!", window) # Bold text using HTML
label.setFont(QFont('Arial', 14))
label.setStyleSheet("color: rgb(0, 128, 0);") # Green text color
label.show()
window.show()
sys.exit(app.exec_())
This example demonstrates setting a specific font (Arial, size 14) and a green color using stylesheets. Note the use of HTML tags () for bold text within the label’s text.
3. Precise Text Alignment
Control the text’s position within the QLabel using the setAlignment() method and Qt’s alignment flags.
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget
from PyQt5.QtCore import Qt
app = QApplication(sys.argv)
window = QWidget()
label = QLabel("Centered Text", window)
label.setAlignment(Qt.AlignCenter) # Center alignment
label.show()
window.show()
sys.exit(app.exec_())
This centers the text. Explore other flags like Qt.AlignRight, Qt.AlignTop, Qt.AlignBottom, and their combinations for fine-grained control.
4. Displaying Images with QLabel
QLabel isn’t just for text; it can also display images. Use the setPixmap() method with a QPixmap object.
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget
from PyQt5.QtGui import QPixmap
from PyQt5.QtCore import Qt
app = QApplication(sys.argv)
window = QWidget()
pixmap = QPixmap('path/to/your/image.png') # Replace with your image path
label = QLabel(window)
label.setPixmap(pixmap)
label.setAlignment(Qt.AlignCenter)
label.show()
window.show()
sys.exit(app.exec_())
Remember to replace 'path/to/your/image.png' with the actual path to your image file.
5. Word Wrapping and Text Size Adjustment
For long text strings, enable word wrapping to prevent text from overflowing the label’s boundaries. You can also adjust the label’s size policy to accommodate the text.
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QWidget
from PyQt5.QtCore import Qt
app = QApplication(sys.argv)
window = QWidget()
label = QLabel("This is a long text string that needs word wrapping.", window)
label.setWordWrap(True) # Enable word wrapping
label.adjustSize() # Adjust label size to fit text
label.show()
window.show()
sys.exit(app.exec_())
setWordWrap(True) activates word wrapping, and adjustSize() ensures the label automatically resizes to fit the wrapped text.
6. Advanced Techniques: Signals and Slots
QLabel can emit signals, enabling interaction with other parts of your application. For example, you can connect a signal to a slot to perform actions when the label is clicked.
(Example using mousePressEvent omitted for brevity, but easily found in PyQt5 documentation)