Building Cross-Platform Desktop Applications with PyQt: A Beginner's Guide

Introduction to PyQt

Graphical User Interfaces, or GUIs, are an integral element of modern computing. From operating systems to mobile applications, every software uses GUIs to enhance user experience.

Developers use various libraries and tools to build GUIs in accordance with their requirements and preferences. Python is a popular choice among developers for building versatile and interactive desktop applications.

Python offers a range of libraries that simplify the task of building GUI applications. One such library is PyQt, which stands for Python Qt. PyQt is a set of Python bindings for the Qt application framework that helps developers create robust, cross-platform desktop applications.

In this tutorial, we will delve into the features and applications of PyQt to help you build your own desktop applications.

Getting to Know PyQt

PyQt was first introduced in 1999 by Riverbank Computing Limited, and has undergone several iterations since then. PyQt6 is the latest version of the framework, which has replaced the older PyQt5.

PyQt6 is available under both GPL and commercial licenses, offering greater flexibility and choice to developers. PyQt6 is designed to enable developers to create rich and responsive desktop applications with ease.

One of its notable features is the widget toolkit, which includes more than 450 customizable graphical components. This toolkit allows developers to create buttons, text boxes, sliders, progress bars, and more, with ease.

PyQt6 also supports event handling, robust signal and slot mechanism, and powerful threading capabilities. PyQt6 provides extensive support for internationalization and localization, making it easier for developers to translate their applications into different languages.

The framework also offers 2D and 3D graphics capabilities and supports multimedia integration, making it an excellent choice for building media-intensive applications such as video players, editors, and game engines.

Conclusion

We’ve provided an overview of PyQt and its applications, as well as insight into some of its notable features. We hope this tutorial has given you a better idea of how to use PyQt to build your own desktop applications.

Whether you’re building simple applications such as calculators or complex applications such as video editors or game engines, PyQt makes it easy and efficient to build them. With its extensive toolkit and support, it’s no surprise that PyQt is one of the most popular libraries for building rich and responsive desktop applications.

3) Installing PyQt

The installation process for PyQt depends on the platform you’re using. PyQt supports a range of platforms, including Windows, macOS, and Linux.

You can install PyQt in two ways: system-wide installation or platform-specific installation. System-wide installation is suitable if you want to use PyQt across multiple projects without having to install it every time.

To install PyQt system-wide, you need to download and install the package from the official PyQt website. On Windows, you can use pip commands to install PyQt system-wide.

On macOS, you can use Homebrew to install PyQt system-wide. On Linux, you can use the package manager to install PyQt system-wide.

Platform-specific installation is suitable if you want to install PyQt for a specific project. To install PyQt for a specific project, you can use pip commands to install PyQt in a virtual environment.

Using a virtual environment can help you manage dependencies and avoid conflicting versions between different projects. To create a virtual environment for PyQt, you can use the “venv” module on Python 3 or the “virtualenv” module on Python 2.

Once you create a virtual environment, you can activate it and use pip commands to install PyQt as follows:

For Python 3:

python3 -m venv myenv
source myenv/bin/activate
pip install PyQt6

For Python 2:

virtualenv myenv
source myenv/bin/activate
pip install PyQt5

4) Creating Your First PyQt Application

To create your first PyQt application, we will create a simple Hello, World! program. Here are the step-by-step instructions:

Step 1: Import the necessary modules

import sys
from PyQt6.QtWidgets import QApplication, QWidget, QLabel

In these lines, we import the “sys” module, which we will use to exit the application, and the “QApplication”, “QWidget”, and “QLabel” classes from the PyQt6 “QtWidgets” module. Step 2: Create the QApplication

app = QApplication(sys.argv)

In this line, we create a QApplication object that represents the application itself.

The “sys.argv” argument is a list of command-line arguments passed to the application. Step 3: Create the GUI

window = QWidget()
window.setWindowTitle("Hello, World!")
label = QLabel("Hello, World!", parent=window)
window.show()

In these lines, we create a QWidget object that represents the main window of the application.

We set the window title to “Hello, World!” using the “setWindowTitle” method. We also create a QLabel object that displays the “Hello, World!” text.

We set the parent of the QLabel object to the main window using the “parent” argument. Finally, we show the window using the “show” method.

Step 4: Start the event loop

sys.exit(app.exec())

In this line, we start the event loop using the “exec” method of the QApplication object. The event loop waits for events such as mouse clicks and keyboard presses and handles them appropriately.

We also use the “sys.exit” method to exit the application when the event loop is terminated. Widgets are the building blocks of PyQt applications.

Widgets are graphical elements such as buttons, text boxes, and labels that users can interact with. You can create widgets using the various classes provided by the PyQt6 “QtWidgets” module.

Once you create widgets, you can arrange them in layouts using the various layout classes provided by the “QtWidgets” module. Layouts help you position widgets in the main window according to your requirements.

Conclusion

We have covered the installation process for PyQt and provided step-by-step instructions for creating a simple Hello, World! application using PyQt. We have also discussed the use of widgets as building blocks for PyQt applications. With these tools, you can start building your own PyQt applications and take advantage of its versatile and responsive capabilities.

5) Learning the Basics of PyQt

PyQt is a comprehensive toolkit for building desktop applications in Python. PyQt applications consist of various components, including widgets, layout managers, dialogs, main windows, applications, event loops, signals and slots.

Widgets are graphical components that users can interact with in an application. PyQt provides a wide range of widgets, including buttons, labels, line edits, combo boxes, radio buttons, and more.

Widgets have attributes that determine their appearance and behavior, and methods that you can use to manipulate them. Layout managers are container objects that help you position widgets in a window.

PyQt provides several layout managers, including QBoxLayout, QGridLayout, and QHBoxLayout. Layout managers help you arrange widgets in the main window according to your requirements, and they automatically adjust the size and position of the widgets when the window is resized.

Dialogs are windows that appear on top of the main window to display information or solicit user input. PyQt provides several built-in dialogs, including QMessageBox, QFileDialog, and QColorDialog.

You can also create custom dialogs for your application using the QDialog class. Main windows are the top-level windows in a PyQt application.

They typically contain the menu bar, toolbar, status bar, and main widget area. The QMainWindow class provides a pre-built main window that you can customize according to your requirements.

Applications are instances of the QApplication class that represent the application itself. The application object manages the event loop, which waits for user input and handles it appropriately.

The QApplication class provides several methods for setting application properties and managing the event loop. Signals and slots are a powerful mechanism for communicating between widgets in a PyQt application.

Signals are emitted when a certain event occurs, such as a button being clicked. Slots are Python functions that are called when a signal is emitted.

You can connect signals to slots using the connect() method, which allows for communication between widgets in a PyQt application.

6) Creating a Calculator App with Python and PyQt

A calculator app is a common application to build when learning PyQt. The application involves creating a simple GUI that can perform basic arithmetic calculations. Here are the step-by-step instructions for creating a calculator application using PyQt:

Creating the Skeleton

Import the necessary modules.

import sys
from PyQt6.QtWidgets import QApplication, QMainWindow, QWidget, QLabel, QPushButton, QVBoxLayout, QHBoxLayout

Create the QApplication object.

app = QApplication(sys.argv)

Create the QMainWindow object.

window = QMainWindow()

Create the central widget for the main window.

main_widget = QWidget()
window.setCentralWidget(main_widget)

Create the QVBoxLayout object to add to main_widget.

layout = QVBoxLayout()
main_widget.setLayout(layout)

Completing the View

Create the QLineEdit for input and display.

input_display = QLineEdit()
layout.addWidget(input_display)

Create the QHBoxLayout object for the first row of buttons.

row_1 = QHBoxLayout()
layout.addLayout(row_1)

Button creation for row 1.

btn_7 = QPushButton('7')
row_1.addWidget(btn_7)
btn_8 = QPushButton('8')
row_1.addWidget(btn_8)
btn_9 = QPushButton('9')
row_1.addWidget(btn_9)
btn_add = QPushButton('+')
row_1.addWidget(btn_add)

Create the QHBoxLayout object for the second row of buttons.

row_2 = QHBoxLayout()
layout.addLayout(row_2)

Button creation for row 2.

btn_4 = QPushButton('4')
row_2.addWidget(btn_4)
btn_5 = QPushButton('5')
row_2.addWidget(btn_5)
btn_6 = QPushButton('6')
row_2.addWidget(btn_6)
btn_subtract = QPushButton('-')
row_2.addWidget(btn_subtract)

Create the QHBoxLayout object for the third row of buttons.

row_3 = QHBoxLayout()
layout.addLayout(row_3)

Button creation for row 3.

btn_1 = QPushButton('1')
row_3.addWidget(btn_1)
btn_2 = QPushButton('2')
row_3.addWidget(btn_2)
btn_3 = QPushButton('3')
row_3.addWidget(btn_3)
btn_multiply = QPushButton('*')
row_3.addWidget(btn_multiply)

Create the QHBoxLayout object for the fourth row of buttons.

row_4 = QHBoxLayout()
layout.addLayout(row_4)

Button creation for row 4.

btn_clear = QPushButton('C')
row_4.addWidget(btn_clear)
btn_0 = QPushButton('0')
row_4.addWidget(btn_0)
btn_equals = QPushButton('=')
row_4.addWidget(btn_equals)
btn_divide = QPushButton('/')
row_4.addWidget(btn_divide)

Implementing the Model

Create a function for evaluating the expression.

def evaluate():
    input_text = input_display.text()
    result = eval(input_text)
    input_display.setText(str(result))

Creating the Controller Class

Create the Calculator class that inherits from QMainWindow.

class Calculator(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setupUI()
    def setupUI(self):
        self.setWindowTitle('Calculator')
        main_widget = QWidget()
        self.setCentralWidget(main_widget)
        layout = QVBoxLayout()
        main_widget.setLayout(layout)
        input_display = QLineEdit()
        layout.addWidget(input_display)
        row_1 = QHBoxLayout()
        layout.addLayout(row_1)
        btn_7 = QPushButton('7')
        row_1.addWidget(btn_7)
        btn_8 = QPushButton('8')
        row_1.addWidget(btn_8)
        btn_9 = QPushButton('9')
        row_1.addWidget(btn_9)
        btn_add = QPushButton('+')
        row_1.addWidget(btn_add)
        row_2 = QHBoxLayout()
        layout.addLayout(row_2)
        btn_4 = QPushButton('4')
        row_2.addWidget(btn_4)
        btn_5 = QPushButton('5')
        row_2.addWidget(btn_5)
        btn_6 = QPushButton('6')
        row_2.addWidget(btn_6)
        btn_subtract = QPushButton('-')
        row_2.addWidget(btn_subtract)
        row_3 = QHBoxLayout()
        layout.addLayout(row_3)
        btn_1 = QPushButton('1')
        row_3.addWidget(btn_1)
        btn_2 = QPushButton('2')
        row_3.addWidget(btn_2)
        btn_3 = QPushButton('3')
        row_3.addWidget(btn_3)
        btn_multiply = QPushButton('*')
        row_3.addWidget(btn_multiply)
        row_4 = QHBoxLayout()
        layout.addLayout(row_4)
        btn_clear = QPushButton('C')
        row_4.addWidget(btn_clear)
        btn_0 = QPushButton('0')
        row_4.addWidget(btn_0)
        btn_equals = QPushButton('=')
        row_4.addWidget(btn_equals)
        btn_divide = QPushButton('/')
        row_4.addWidget(btn_divide)
        btn_0.clicked.connect(lambda: input_display.setText(input_display.text() + '0'))
        btn_1.clicked.connect(lambda: input_display.setText(input_display.text() + '1'))
        btn_2.clicked.connect(lambda: input_display.setText(input_display.text() + '2'))
        btn_3.clicked.connect(lambda: input_display.setText(input_display.text() + '3'))
        btn_4.clicked.connect(lambda: input_display.setText(input_display.text() + '4'))
        btn_5.clicked.connect(lambda: input_display.setText(input_display.text() + '5'))
        btn_6.clicked.connect(lambda: input_display.setText(input_display.text() + '6'))
        btn_7.clicked.connect(lambda: input_display.setText(input_display.text() + '7'))
        btn_8.clicked.connect(lambda: input_display.setText(input_display.text() + '8'))
        btn_9.clicked.connect(lambda: input_display.setText(input_display.text() + '9'))
        btn_add.clicked.connect(lambda: input_display.setText(input_display.text() + '+'))
        btn_subtract.clicked.connect(lambda: input_display.setText(input_display.text() + '-'))
        btn_multiply.clicked.connect(lambda: input_display.setText(input_display.text() + '*'))
        btn_divide.clicked.connect(lambda: input_display.setText(input_display.text() + '/'))
        btn_clear.clicked.connect(lambda: input_display.setText(''))
        btn_equals.clicked.connect(evaluate)
        self.show()

As shown above, we created four main sections for building the Calculator application: the skeleton, the view, the model, and creating the controller class. We used several PyQt widgets like `QLineEdit`, `QPushButton`, and `QVBoxLayout`.

We also utilized signals and slots to connect the widgets to functions that handle the application’s logic. With this example, we hope that you can create more complex applications on your own using PyQt.

7) Additional Tools

While PyQt is known for making it easy to build desktop applications in Python, there are additional tools and resources that can make the process even simpler and more efficient. Two such tools are PyQt Designer and QML.

PyQt Designer is a visual tool for creating GUIs without having to write any code. It is a part of the Qt toolkit and comes bundled with PyQt. With PyQt Designer, you can drag and drop widgets into a graphical interface and customize their properties and behavior using a graphical user interface.

PyQt Designer generates a .ui file that you can load into your Python code using the uic.loadUi() function. This file contains the XML definition of the GUI, which can be loaded and used in Python code like any other PyQt widget.

QML, or Qt Markup Language, is a declarative language for creating user interfaces. It is based on JavaScript and provides a more flexible and powerful way to create user interfaces compared to traditional widget-based approaches.

QML is often used in conjunction with C++, but it can also be used with Python using the PySide2 library. QML provides a more modern and streamlined approach to creating user interfaces, and it can be used to create complex and visually appealing applications.

Adventures in Machine Learning

Building Cross-Platform Desktop Applications with PyQt: A Beginner’s Guide

Introduction to PyQt

Getting to Know PyQt

Conclusion

3) Installing PyQt

For Python 3:

For Python 2:

4) Creating Your First PyQt Application

Conclusion

5) Learning the Basics of PyQt

6) Creating a Calculator App with Python and PyQt

Creating the Skeleton

Completing the View

Implementing the Model

Creating the Controller Class

7) Additional Tools

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