Python PyQt

PyQt is a powerful Python library for creating graphical user interfaces (GUIs), which can be used as an alternative to Python’s built-in Tkinter.

PyQt is the Python binding for the Qt framework and is widely used in desktop application development.

Qt is a cross-platform C++ application development framework.

PyQt allows Python developers to leverage the Qt library to create powerful GUI applications.

PyQt has the following major versions:

• PyQt4: Binding based on Qt4
• PyQt5: Binding based on Qt5
• PyQt6: Binding based on Qt6 (latest version)

Installing PyQt

Install PyQt5 using pip:

# Install PyQt5
pip install PyQt5

# Install Qt Designer and other tools (optional)
pip install PyQt5-tools

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Your First PyQt Program

Creating a Simple Window

Below is the most basic PyQt program, creating a blank window:

Example

from PyQt5.QtWidgets import QApplication, QWidget

# Create an application instance
app = QApplication([])

# Create the main window
window = QWidget()
window.setWindowTitle("My First PyQt Program")
window.setGeometry(100, 100, 400, 300)  # (x, y, width, height)

# Show the window
window.show()

# Run the application
app.exec_()

Code Explanation

1. QApplication: Manages the control flow and main settings of the GUI application.
2. QWidget: The most basic window class; all UI components inherit from it.
3. setWindowTitle(): Sets the window title.
4. setGeometry(): Sets the window position and size.
5. show(): Displays the window.
6. app.exec_(): Starts the event loop, waiting for user interaction.

A typical PyQt application consists of the following parts:

1. QApplication Object: Every PyQt application needs a QApplication instance
2. Windows and Widgets: User interface components
3. Event Loop: The loop that handles user input and system events
4. Event Handlers: Functions or methods that respond to events

Example

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        
        # Set window title and size
        self.setWindowTitle("My First PyQt Application")
        self.setGeometry(100, 100, 400, 300)  # x, y, width, height
        
        # Create a button
        self.button = QPushButton("Click Me", self)
        self.button.setGeometry(150, 150, 100, 30)
        self.button.clicked.connect(self.button_clicked)
        
    def button_clicked(self):
        print("Button was clicked!")

if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

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Common PyQt Widgets

Button (QPushButton)

Example

from PyQt5.QtWidgets import QPushButton

button = QPushButton("Click Me", window)
button.move(150, 150)  # Set button position

Label (QLabel)

Example

from PyQt5.QtWidgets import QLabel

label = QLabel("Hello PyQt!", window)
label.move(100, 100)

Text Box (QLineEdit)

Example

from PyQt5.QtWidgets import QLineEdit

textbox = QLineEdit(window)
textbox.move(100, 50)

For more common widget content, refer to: https://www.runoob.com/python3/python-pyqt-widgets.html

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Layout Management (QVBoxLayout)

Using layout managers allows automatic adjustment of widget positions:

Example

from PyQt5.QtWidgets import QVBoxLayout, QLabel, QPushButton

layout = QVBoxLayout()
layout.addWidget(QLabel("Username"))
layout.addWidget(QLineEdit())
layout.addWidget(QPushButton("Login"))
window.setLayout(layout)

For more layout management content, refer to: https://www.runoob.com/python3/python-pyqt-layout.html

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Signals and Slots Mechanism

PyQt uses the Signal and Slot mechanism to handle events.

PyQt’s signal and slot mechanism is the core mechanism for communication between objects.

• Signal: A notification emitted when a specific event occurs
• Slot: A function or method that responds to a signal

Example

from PyQt5.QtWidgets import QPushButton

def on_button_click():
    print("Button was clicked!")

button = QPushButton("Click Me", window)
button.clicked.connect(on_button_click)  # Connect signal and slot

Custom Signals

Example

from PyQt5.QtCore import pyqtSignal, QObject

class MyEmitter(QObject):
    my_signal = pyqtSignal(str)  # Define a signal

emitter = MyEmitter()
emitter.my_signal.connect(lambda x: print(f"Signal received: {x}"))
emitter.my_signal.emit("Hello")  # Emit the signal

For more signals and slots content, refer to: https://www.runoob.com/python3/python-pyqt-signals-and-slots.html

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Using Qt Designer

Qt Designer is a visual design tool that allows you to drag and drop widgets to design interfaces:

• Launch Designer (usually located in the Python installation directory under Lib\site-packages\qt5_applications\Qt\bin)

• Design the interface and save it as a .ui file

• Convert the .ui file to Python code:

  pyuic5 input.ui -o output.py

Using the generated interface in code:

Example

from PyQt5 import uic

# Load the UI file
Form, Window = uic.loadUiType("output.ui")

# Use the UI
app = QApplication(sys.argv)
window = Window()
form = Form()
form.setupUi(window)
window.show()
sys.exit(app.exec_())

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Hands-on: A Simple Notepad Application

Interface Design

Example

import sys
from PyQt5.QtWidgets import (QApplication, QMainWindow, QTextEdit, 
                            QAction, QFileDialog, QMessageBox)

class Notepad(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()
        
    def initUI(self):
        self.text_edit = QTextEdit(self)
        self.setCentralWidget(self.text_edit)
        
        self.create_actions()
        self.create_menus()
        
        self.setWindowTitle('Simple Notepad')
        self.setGeometry(100, 100, 800, 600)
        
    def create_actions(self):
        # File menu actions
        self.new_action = QAction('New', self)
        self.new_action.setShortcut('Ctrl+N')
        self.new_action.triggered.connect(self.new_file)
        
        self.open_action = QAction('Open', self)
        self.open_action.setShortcut('Ctrl+O')
        self.open_action.triggered.connect(self.open_file)
        
        self.save_action = QAction('Save', self)
        self.save_action.setShortcut('Ctrl+S')
        self.save_action.triggered.connect(self.save_file)
        
        self.exit_action = QAction('Exit', self)
        self.exit_action.setShortcut('Ctrl+Q')
        self.exit_action.triggered.connect(self.close)
        
        # Edit menu actions
        self.copy_action = QAction('Copy', self)
        self.copy_action.setShortcut('Ctrl+C')
        self.copy_action.triggered.connect(self.text_edit.copy)
        
        self.paste_action = QAction('Paste', self)
        self.paste_action.setShortcut('Ctrl+V')
        self.paste_action.triggered.connect(self.text_edit.paste)
        
        self.cut_action = QAction('Cut', self)
        self.cut_action.setShortcut('Ctrl+X')
        self.cut_action.triggered.connect(self.text_edit.cut)
        
    def create_menus(self):
        menubar = self.menuBar()
        
        # File menu
        file_menu = menubar.addMenu('File')
        file_menu.addAction(self.new_action)
        file_menu.addAction(self.open_action)
        file_menu.addAction(self.save_action)
        file_menu.addSeparator()
        file_menu.addAction(self.exit_action)
        
        # Edit menu
        edit_menu = menubar.addMenu('Edit')
        edit_menu.addAction(self.copy_action)
        edit_menu.addAction(self.paste_action)
        edit_menu.addAction(self.cut_action)
        
    def new_file(self):
        self.text_edit.clear()
        
    def open_file(self):
        filename, _ = QFileDialog.getOpenFileName(self, 'Open File')
        if filename:
            try:
                with open(filename, 'r') as f:
                    self.text_edit.setText(f.read())
            except Exception as e:
                QMessageBox.warning(self, 'Error', f'Cannot open file: {e}')
                
    def save_file(self):
        filename, _ = QFileDialog.getSaveFileName(self, 'Save File')
        if filename:
            try:
                with open(filename, 'w') as f:
                    f.write(self.text_edit.toPlainText())
            except Exception as e:
                QMessageBox.warning(self, 'Error', f'Cannot save file: {e}')

if __name__ == '__main__':
    app = QApplication(sys.argv)
    notepad = Notepad()
    notepad.show()
    sys.exit(app.exec_())

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PyQt5 Core Components

Most widgets are located in PyQt5.QtWidgets.

Advanced features (such as multimedia, networking) may require other modules (such as QtCore, QtGui, QtNetwork, etc.).

QListView/QTableView/QTreeView need to be used with data models (such as QStandardItemModel) for greater flexibility.

Other installable extensions:

pip install PyQtWebEngine  # Web support
pip install PyQtChart      # Chart support

Widget Category	Widget Name	Module	Description
Basic Window Widgets	QWidget	QtWidgets	Base class for all user interface objects, can be used as a blank window or container
	QMainWindow	QtWidgets	Main window framework, includes menu bar, toolbar, status bar, etc.
	QDialog	QtWidgets	Dialog base class, used for pop-up windows
Layout Management	QVBoxLayout	QtWidgets	Vertical layout manager
	QHBoxLayout	QtWidgets	Horizontal layout manager
	QGridLayout	QtWidgets	Grid layout manager
	QFormLayout	QtWidgets	Form layout manager (label + input field pairs)
Button Widgets	QPushButton	QtWidgets	Regular button
	QRadioButton	QtWidgets	Radio button
	QCheckBox	QtWidgets	Checkbox
	QToolButton	QtWidgets	Toolbar button (can have icons)
Input Widgets	QLineEdit	QtWidgets	Single-line text input box
	QTextEdit	QtWidgets	Multi-line rich text editor (supports HTML)
	QPlainTextEdit	QtWidgets	Multi-line plain text editor
	QSpinBox	QtWidgets	Integer spin box
	QDoubleSpinBox	QtWidgets	Floating-point spin box
	QComboBox	QtWidgets	Dropdown selection box
	QDateEdit	QtWidgets	Date picker
	QTimeEdit	QtWidgets	Time picker
	QDateTimeEdit	QtWidgets	Date and time picker
	QSlider	QtWidgets	Slider (horizontal/vertical)
	QDial	QtWidgets	Dial knob widget
Display Widgets	QLabel	QtWidgets	Text/image label
	QLCDNumber	QtWidgets	LCD number display
	QProgressBar	QtWidgets	Progress bar
	QStatusBar	QtWidgets	Status bar (usually used with QMainWindow)
Container Widgets	QGroupBox	QtWidgets	Group box (container with a title)
	QTabWidget	QtWidgets	Tab container
	QStackedWidget	QtWidgets	Stacked container (shows one child widget at a time)
	QScrollArea	QtWidgets	Scroll area container
	QMdiArea	QtWidgets	MDI (Multiple Document Interface) area
List/Table/Tree	QListWidget	QtWidgets	List widget (with item management)
	QTreeWidget	QtWidgets	Tree widget
	QTableWidget	QtWidgets	Table widget
	QListView	QtWidgets	List view (requires data model)
	QTableView	QtWidgets	Table view (requires data model)
	QTreeView	QtWidgets	Tree view (requires data model)
Menu/Toolbar	QMenuBar	QtWidgets	Menu bar
	QMenu	QtWidgets	Menu (can contain submenus and actions)
	QToolBar	QtWidgets	Toolbar
	QAction	QtWidgets	Action (used for menu items, toolbar buttons, etc.)
Dialogs	QFileDialog	QtWidgets	File selection dialog
	QColorDialog	QtWidgets	Color selection dialog
	QFontDialog	QtWidgets	Font selection dialog
	QInputDialog	QtWidgets	Input dialog (text, numbers, etc.)
	QMessageBox	QtWidgets	Message box (warning, error, question, etc.)
Graphics View	QGraphicsView	QtWidgets	Graphics view framework (for 2D graphics)
	QGraphicsScene	QtWidgets	Graphics scene (used with QGraphicsView)
Other Feature Widgets	QCalendarWidget	QtWidgets	Calendar widget
	QSplashScreen	QtWidgets	Splash screen
	QSystemTrayIcon	QtWidgets	System tray icon
	QWebEngineView	QtWebEngineWidgets	Web browser component (requires separate PyQtWebEngine installation)

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Learning Resources

• PyQt Official Website
• PyQt5 Official Documentation
• PyQt6 Official Documentation
• Qt Official Documentation