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Herausgeber: Packt Publishing
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

Over 60 recipes to help you design interactive, smart, and cross-platform GUI applications

Key Features

Get succinct QT solutions to pressing GUI programming problems in Python

Learn how to effectively implement reactive programming

Build customized applications that are robust and reliable

Book Description

As you expand your GUI using more widgets, you will cover networks, databases, and graphical libraries that greatly enhance its functionality. Next, the book guides you in using Qt Designer to design user interfaces and implementing and testing dialogs, events, the clipboard, and drag and drop functionality to customize your GUI. You will learn a variety of topics, such as look and feel customization, GUI animation, graphics rendering, implementing Google Maps, and more. Lastly, the book takes you through how Qt5 can help you to create cross-platform apps that are compatible with Android and iOS. You will be able to develop functional and appealing software using PyQt through interesting and fun recipes that will expand your knowledge of GUIs

What you will learn

Use basic Qt components, such as a radio button, combo box, and sliders

Use QSpinBox and sliders to handle different signals generated on mouse clicks

Work with different Qt layouts to meet user interface requirements

Create custom widgets and set up customizations in your GUI

Perform asynchronous I/O operations and thread handling in the Python GUI

Employ network concepts, internet browsing, and Google Maps in UI

Use graphics rendering and implement animation in your GUI

Make your GUI application compatible with Android and iOS devices

Who this book is for

If you're an intermediate Python programmer wishing to enhance your coding skills by writing powerful GUIs in Python using PyQT, this is the book for you.

Details

Das E-Book können Sie in Legimi-Apps oder einer beliebigen App lesen, die das folgende Format unterstützen:

EPUB

Seitenzahl: 444

Veröffentlichungsjahr: 2018

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Leseprobe

Qt5 Python GUI Programming Cookbook

Building responsive and powerful cross-platform applications with PyQt

B.M. Harwani

BIRMINGHAM - MUMBAI

Qt5 Python GUI Programming Cookbook

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing or its dealers and distributors, will be held liable for any damages caused or alleged to have been caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

Commissioning Editor: Richa TripathiAcquisition Editor: Alok Dhuri Content Development Editor: Zeeyan PinheiroTechnical Editor: Vibhuti GawdeCopy Editor: Safis EditingProject Coordinator: Vaidehi SawantProofreader: Safis EditingIndexer: Rekha NairGraphics: Jason MonteiroProduction Coordinator: Nilesh Mohite

First published: July 2018

Production reference: 1270718

Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK.

ISBN 978-1-78883-100-0

www.packtpub.com

I am thankful to my family—my small world: Anushka (my wife) and my two little darlings, Chirag and Naman, for allowing me to work on the book even during time that I was supposed to spend with them.

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Contributors

About the author

B.M. Harwani is the founder and owner of Microchip Computer Education (MCE), based in Ajmer, India. He graduated with a BE in computer engineering from the University of Pune and also has a C level (masters diploma in computer technology) from DOEACC, Government of India. Having been involved in the teaching field for over 20 years, he has developed the art of explaining even the most complicated topics in a straightforward and easily understandable fashion. He is also a renowned speaker and the author of several books. To learn more, visit his blog, a site that helps programmers.

A big thank you to the entire editorial team at Packt, who worked tirelessly to produce this book. Really, I enjoyed working with each of you. I should not forget to thank my dear students, who have been a good teacher for me as they make me understand the basic problems they face in a subject and enable me to directly hit those topics. The endless interesting queries from my students help me write books with a practical approach.

About the reviewers

Marcus Ottosson is a company director, software developer, and artist with a decade of experience in the film and visual effects industry. He has built countless user interfaces and tools with Python and Qt for projects such as Marvel’s Doctor Strange and Alfonso Cuaron’s Gravity. He has written several Python frameworks for use in the creation of film and games, such as Pyblish and Avalon, along with PyQt, a compatibility wrapper around all the available bindings of Qt for Python.

Sivan Grünberg has close to 20 years of multidisciplinary IT expertise and a razor-sharp eye for quality. A long-time open source devotee, his contributions can be found, literally, all over open source. He has been utilizing the Python ecosystem for R&D endeavors ever since it was pitched to him by The SABDFL and Ubuntu. Alongside Shir, a product, content, and operations expert, he runs Vitakka.co, providing infrastructure consulting and coding solutions in all-things digital.

My amazing family, Eric, Helena, Shir, Moshik, and the Debian/Ubuntu, Python, GNOME, and KDE communities—without you, these lines would have never been written.

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Title Page

Qt5 Python GUI Programming Cookbook

Dedication

Packt Upsell

Why subscribe?

PacktPub.com

Contributors

About the author

About the reviewers

Packt is searching for authors like you

Preface

Who this book is for

What this book covers

To get the most out of this book

Download the example code files

Download the color images

Conventions used

Sections

Getting ready

How to do it…

How it works…

There's more…

Preface

PyQt is one of the best cross-platform interface toolkits currently available; it's stable, mature, and completely native. If you want control over all aspects of UI elements, PyQt is what you need. This book will guide you through every concept you need to create fully functional GUI applications using PyQT, with only a few lines of code.As you expand your GUI using more widgets, you will cover networks, databases, and graphical libraries that greatly enhance its functionality. The book shows you how to use QT Designer to design user interfaces and implement and test dialogs, events, the clipboard, and drag and drop functionality to customize your GUI. You will learn a variety of topics, such as look and feel customization, GUI animation, graphics rendering, implementing Google Maps, and more. Lastly, the book takes you through how Qt5 can help you create cross-platform apps that are compatible with Android and iOS. You will be able to develop functional and appealing software using PyQt through interesting and fun recipes that will expand your knowledge of GUIs.

Who this book is for

This book is meant for intermediate to advanced programmers and developers who have some preliminary knowledge of Python programming. This book can be of great use for trainers, teachers, and software developers who wish to build a fully-featured GUI-based application in Python.

What this book covers

Chapter 1, Creating a User Interface with Qt Components, teaches readers to use certain basic widgets of Qt Designer and how to display a welcome message along with the username. You will also be learning how to choose one out of several options using radio buttons and choose more than one out of several options by making use of checkboxes.

Chapter 2, Event Handling – Signals and Slots, covers how to execute specific tasks on the occurrence of certain events on any widget, how to copy and paste text from one Line Edit widget to another, convert data types and make a small calculator, and use spin boxes, scrollbars, and sliders. You will also learn to perform multiple tasks using the List Widget.

Chapter 3, Working with Date and Time, focuses on learning how to display the system clock time using an LCD, show the date selected by the user from Calendar Widget, create a hotel reservation form, and display tabular data using Table widget.

Chapter 4, Understanding OOP Concepts, discusses object-oriented programming concepts such as how to use classes, single inheritance, multilevel inheritance in GUI applications, and multiple inheritance.

Chapter 5, Understanding Dialogs, explores the use of certain dialogs, where each dialog is meant for fetching a different kind of information. You will also learn to take input from the user using input dialog.

Chapter 6, Understanding Layouts, explains how to arrange widgets horizontally, vertically, and in different layouts by making use of Horizontal Layout, Vertical Layout, Grid Layout, and arranging widgets in two column layout using Form Layout.

Chapter 7, Networking and Managing Large Documents, demonstrates how to make a small browser, establish a connection between client and server, create a dockable and floatable sign in form, and manage more than one document using MDI. Also, you will be learn how to display information in sections using the Tab widget. You will learn how to create a custom menu bar that invokes different graphics tools when a specific menu item is chosen.

Chapter 8, Doing Asynchronous Programming in Python, looks at the concept of asynchronous operations using threads. To see the impact of asynchronous operations on GUIs, you will be making use of a progress bar, that is, the progress bars will be updated through threads asynchronously.

Chapter 9, Database Handling, outlines how to manage a SQLite database to keep information for future use. Using the knowledge gained, you will learn to make a signin form that checks whether a user's email address and password are correct or not.

Chapter 10, Using Graphics, explains how to display certain graphics in the application. You will also learn how to create a toolbar of your own that contains certain tools that can be used to draw different graphics.

Chapter 11, Implementing Animation, features how to display a 2D graphical image, make a ball move down on the click of a button, make a bouncing ball, and make a ball animate as per the specified curve.

Chapter 12, Using Google Maps, showcases how to use the Google API to display location and other information. You will learn to derive the distance between two locations and display location on Google Maps on the basis of longitude and latitude values that are entered.

Chapter 13, Running Python Scripts on Android and iOS devices, takes you through how to use QPython to run Python scripts on Android devices. You will learn how to package Kivy Python scripts on Android and iOS devices. You will be making several applications for mobile devices, such as prompting for the user’s name and displaying a welcome message, understanding different buttons in a Dialog box, performing single and multiple selections from a list, selecting date using a Date Picker dialog, capturing images using a camera, making Android devices speak text, creating cross-platform Python scripts using Kivy, packaging Python scripts into the Android APK using Buildozer, and packaging Python scripts for iOS.

To get the most out of this book

You need to have some preliminary knowledge of Python programming. You need to install Python and PyQt5. The steps to install Python and PyQt are explained in the Appendix. To run Python script on Android devices, you need to install QPython on your Android device. To package Python scripts into Android’s APK using the Kivy library, you need to install Kivy, a Virtual Box, and Buildozer packager. Similarly, to run Python scripts on iOS devices, you need a macOS machine and some library tools, including Cython. The steps to install these software are explained in Chapter 13, Running Python Scripts on Android and iOS.

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Sections

In this book, you will find several headings that appear frequently (Getting ready,How to do it..., How it works..., There's more..., and Seealso).

To give clear instructions on how to complete a recipe, use these sections as follows:

Getting ready

This section tells you what to expect in the recipe and describes how to set up any software or anypreliminary settings required for the recipe.

How to do it…

This section contains the steps required to follow the recipe.

How it works…

This section usually consists of a detailed explanation of what happened in the previous section.

There's more…

This section consists of additional information about the recipe in order to make you moreknowledgeable about the recipe.

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Creating a User Interface with Qt Components

In this chapter, we will learn to use the following widgets:

Displaying a welcome message

Using the Radio Button widget

Grouping radio buttons

Displaying options in the form of checkboxes

Displaying two groups of checkboxes

Introduction

We will be learning to create GUI applications using the Qt toolkit. The Qt toolkit, known simply as Qt, is a cross-platform application and UI framework developed by Trolltech, which is used for developing GUI applications. It runs on several platforms, including Windows, macOS X, Linux, and other UNIX platforms. It is also referred to as a widget toolkit because it provides widgets such as buttons, labels, textboxes, push buttons, and list boxes, which are required for designing a GUI. It includes a cross-platform collection of classes, integrated development tools, and a cross-platform IDE. To create real-time applications, we will be making use of Python bindings for the Qt toolkit called, PyQt5.

PyQt

PyQt is a set of Python bindings for the cross-platform application framework that combines all the advantages of Qt and Python. With PyQt, you can include Qt libraries in Python code, enabling you to write GUI applications in Python. In other words, PyQt allows you to access all the facilities provided by Qt through Python code. Since PyQt depends on the Qt libraries to run, when you install PyQt, the required version of Qt is also installed automatically on your machine.

A GUI application may consist of a main window with several dialogs or just a single dialog. A small GUI application usually consists of at least one dialog. A dialog application contains buttons. It doesn't contain a menu bar, toolbar, status bar, or central widget, whereas a main window application normally has all of those.

Dialogs are of the following two types:

Modal

: This dialog is one that blocks the user from interacting with other parts of the application. The dialog is the only part of the application that the user can interact with. Until the dialog is closed, no other part of the application can be accessed.

Modeless

: This dialog is the opposite of a modal dialog. When a modeless dialog is active, the user is free to interact with the dialog and with the rest of the application.

Ways of creating GUI applications

There are the following two ways to write a GUI application:

From scratch, using a simple text editor

With Qt Designer, a visual design tool with

which you can create a user interface quickly using drag and drop

You will be using Qt Designer to develop GUI applications in PyQt, as it is a quick and easy way to design user interfaces without writing a single line of code. So, launch Qt Designer by double-clicking on its icon on desktop.

On opening, Qt Designer asks you to select a template for your new application, as shown in the following screenshot:

Qt Designer provides a number of templates that are suitable for different kinds of applications. You can choose any of these templates and then click the Create button.

Qt Designer provides the following predefined templates for a new application:

Dialog with Buttons Bottom

: This template creates a form with the

and

Cancel

buttons in the bottom-right corner.

Dialog with Buttons Right

: This template creates a form with the

and

Cancel

buttons in the top-right corner.

Dialog without Buttons

: This template creates an empty form on which you can place widgets. The superclass for dialogs is

QDialog

Main Window

: This template provides a main application window with a menu bar and a toolbar that can be removed if not required.

Widget

: This template creates a form whose superclass is

QWidget

rather than

QDialog

Every GUI application has a top-level widget and the rest of the widgets are called its children. The top-level widget can be QDialog, QWidget, or QMainWindow, depending on the template you require. If you want to create an application based on the dialog template, then the top-level widget or the first class that you inherit will be QDialog. Similarly, to create an application based on the Main Window template, the top-level widget will be QMainWindow, and to create the application based on the Widget template, you need to inherit the QWidget class. As mentioned previously, the rest of the widgets that are used for the user interface are called child widgets of the classes.

Qt Designer displays a menu bar and toolbar at the top. It shows a Widget box on the left that contains a variety of widgets used to develop applications, grouped in sections. All you have to do is drag and drop the widgets you want from the form. You can arrange widgets in layouts, set their appearance, provide initial attributes, and connect their signals to slots.

Displaying a welcome message

In this recipe, the user will be prompted to enter his/her name followed by clicking a push button. On clicking the button, a welcome message will appear, "Hello," followed by the name entered by the user. For this recipe, we need to make use of three widgets, Label, Line Edit, and Push Button. Let's understand these widgets one by one.

Understanding the Label widget

The Label widget is an instance of theQLabelclass and is used for displaying messages and images. Because the Label widgets simply display results of computations and don't take any input, they are simply used for supplying information on the screen.

Methods

The following are the methods provided by the QLabel class:

setText()

: This method assigns text to the

Label

widget

setPixmap()

: This method assigns

pixmap

, an instance of the

QPixmap

class, to the

Label

widget

setNum()

This method a

ssigns an integer or double value to the

Label

widget

clear()

This method c

lears text from the

Label

widget

The default text of QLabel is TextLabel. That is, when you add a QLabel class to a form by dragging a Label widget and dropping it on the form, it will display TextLabel. Besides using setText(), you can also assign text to a selected QLabel object by setting its text property in the Property Editor window.

Understanding the Line Edit widget

The Line Edit widget is that is popularly used for entering single-line data. The Line Edit widget is an instance of the QLineEdit class, and you can not only enter, but also edit the data too. Besides entering data, you can undo, redo, cut, and paste data in the Line Edit widget.

Methods

The following are the methods provided by the QLineEdit class:

setEchoMode()

: It sets the echo mode of the

Line Edit

widget. That is, it determines how the contents of the

Line Edit

widget are to be displayed. The available options are as follows:

Normal

: This is the default mode and it displays characters the way they are entered

NoEcho

: It switches off the

Line Edit

echo, that is, it doesn't display anything

Password

: This option is used for password fields, no text will be displayed; instead, asterisks appear for the text entered by the user

PasswordEchoOnEdit

: It displays the actual text while editing the password fields, otherwise it will display the asterisks for the text

maxLength()

: This method is used to specify the maximum length of text that can be entered in the

Line Edit

widget.

setText()

: This method is used for assigning text to the

Line Edit

widget.

text()

: This method accesses the text entered in the

Line Edit

widget.

clear()

: This method clears or deletes the complete content of the

Line Edit

widget.

setReadOnly()

: When the Boolean value true is passed to this method, it will make the

Line Edit

widget read-only, that is, non-editable. The user cannot make any changes to the contents displayed through the

Line Edit

widget, but can only copy.

isReadOnly()

: This method returns the Boolean value true if the

Line Edit

widget is in read-only mode, otherwise it returns false.

setEnabled()

: By default, the

Line Edit

widget is enabled, that is, the user can make changes to it. But if the Boolean value false is passed to this method, it will disable the

Line Edit

widget so the user cannot edit its content, but can only assign text via the

setText()

method.

setFocus()

: This method positions the cursor on the specified

Line Edit

widget.

Understanding the Push Button widget

To display a push button in an application, you need to create an instance of the QPushButton class. When assigning text to buttons, you can create shortcut keys by preceding any character in the text with an ampersand. For example, if the text assigned to a push button is Click Me, the character C will be underlined to indicate that it is a shortcut key, and the user can select the button by pressing Alt + C. The button emits the clicked() signal if it is activated. Besides text, an icon can also be displayed in the push button. The methods for displaying text and an icon in a push button are as follows:

setText()

: This method is used to assign text to the push button

setIcon()

: This method is used to assign an icon to the push button

How it works...

The demoLineEdit.py file is very easy to understand. A class with the name of the top-level object is created, with Ui_ prepended. Since the top-level object used in our application is Dialog, the Ui_Dialog class is created and stores the interface elements of our widget. That class has two methods, setupUi() and retranslateUi(). The setupUi() method sets up the widgets; it creates the widgets that you use while defining the user interface in Qt Designer. The method creates the widgets one by one and also sets their properties. The setupUi() method takes a single argument, which is the top-level widget in which the user interface (child widgets) is created. In our application, it is an instance of QDialog. The retranslateUi() method translates the interface.

Let's understand what callLineEdit.py does statement-wise:

It imports the necessary modules.

QWidget

is the base class of all user interface objects in PyQt5.

It creates a new

MyForm

class that inherits from the base class,

QDialog

It provides the default constructor for

QDialog

. The default constructor has no parent, and a widget with no parent is known as a window.

Event handling in PyQt5 uses signals and slots. A signal is an event, and a slot is a method that is executed on the occurrence of a signal. For example, when you click a push button, a

clicked()

event, also known as a signal, occurs. The

connect()

method connects signals with slots. In this case, the slot is a method:

dispmessage()

. That is, when the user clicks the push button, the

dispmessage()

method will be invoked.

clicked()

is an event here and an event handling loop waits for an event to occur and then dispatches it to perform some task. The event handling loop continues to work until either the

exit()

method is called or the main widget is destroyed.

It creates an application object with the name

app

through the

QApplication()

method. Every PyQt5 application must create

sys.argv

application object

which contains a list of arguments from the command line, and it is passed to the method while creating the application object. The

sys.argv

parameter helps in passing and controlling the startup attributes of a script.

An instance of the

MyForm

class is created with the name

The

show()

method will display the widget on the screen.

The

dispmessage()

method performs event handling for the push button. It displays the

Hello

text, along with the name entered in the

Line Edit

widget.

The

sys.exit()

method ensures a clean exit, releasing memory resources.

The exec_() method has an underscore because exec is a Python keyword.

On executing the preceding program, you get a window with the Line Edit and Push Button widgets, as shown in the following screenshot. When the push button is selected, the displmessage() method will be executed, displaying the Hello message along with the user's name that is entered in the Line Edit widget:

Using the Radio Button widget

This recipe displays certain flight types via Radio Button and when the user selects the radio button, the price associated with that flight will be displayed. We need to first understand the workings of Radio Button.

Understanding Radio Button

The Radio Button widgets are very popular when you want the user to select only one option out of the available options. Such options are known as mutually exclusive options. When the user selects an option, the previously selected option is automatically deselected. The Radio Button widgets are instances of the QRadioButton class. Every radio button has an associated text label. The radio button can be either in selected (checked) or unselected (unchecked) states. If you want two or more sets of radio buttons, where each set allows the exclusive selection of a radio button, put them into different button groups (instances of QButtonGroup). The methods provided by QRadioButton are shown next.

Methods

The QRadioButton class provides the following methods:

isChecked()

: This method returns the Boolean value true if the button is in the selected state.

setIcon()

: This method displays an icon with the radio button.

setText()

: This method assigns the text to the radio button. If you want to specify a shortcut key for the radio button, precede the preferred character in the text with an ampersand (

). The shortcut character will be underlined.

setChecked()

: To make any radio button appear selected by default, pass the Boolean value true to this method.

Signal description

Signals emitted by QRadioButton are as follows:

toggled()

: This signal is emitted whenever the button changes its state from checked to unchecked or vice versa

clicked()

: This signal is emitted when a button is activated (that is, pressed and released) or when its shortcut key is pressed

stateChanged()

: This signal is emitted when a radio button changes its state from checked to unchecked or vice versa

To understand the concept of radio buttons, let's create an application that asks the user to select the flight type and displays three options, First Class, Business Class, and Economy Class, in the form of radio buttons. On selecting an option through the radio button, the price for that flight will be displayed.

How it works...

The toggled() event of Radio Button is connected to the dispFare() function, which will display the price of the selected flight type. In the dispFare() function, you check the state of the radio buttons. Hence, if radioButtonFirstClass is selected, the value 50 is assigned to the fare variable. Similarly, if radioButtonBusinessClass is selected, the value 125 is assigned to the fare variable. Similarly, the value 100 is assigned to the fare variable when radioButtonEconomyClass is selected. Finally, the value in the fare variable is displayed via labelFare.

On executing the previous program, you get a dialog that displays three flight types and prompts the user to select the one that he/she wants to use for travel. On selecting a flight type, the price of the selected flight type is displayed, as shown in the following screenshot:

Grouping radio buttons

In this application, we will learn to create two groups of radio buttons. The user can select radio buttons from either group and accordingly the result or text will appear on the screen.

Getting ready

We will display a dialog that displays shirts of different sizes and different payment methods. On selecting a shirt size and a payment method, the selected shirt size and payment method will be displayed on the screen. We will create two groups of radio buttons, one of the shirt sizes and other payment methods. The shirt size group displays four radio buttons showing four different types of the size such as M, L, XL, and XXL, where M stands for medium size, L stands for large size, and so on. The payment method group displays three radio buttons, Debit/Credit Card, NetBanking, and Cash On Delivery. The user can select any radio button from either of the groups. When the user selects any of the shirt sizes or payment methods, the selected shirt size and payment method will be displayed.

How it works...

The toggled() event of all the radio buttons is connected to the dispSelected() function, which will display the selected shirt size and payment method. In the dispSelected() function, you check the status of the radio buttons to find out whether they are checked or unchecked. On the basis of the selected radio button in the first vertical layout, the value of the selected1 variable will be set to Medium, Large, Extra Large, or

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Qt5 Python GUI Programming Cookbook E-Book

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Qt5 Python GUI Programming Cookbook

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Contributors

About the author

About the reviewers

Packt is searching for authors like you

Table of Contents

Preface

Who this book is for

What this book covers

To get the most out of this book

Download the example code files

Download the color images

Sections

Getting ready

How to do it…

How it works…

There's more…

See also

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Creating a User Interface with Qt Components

Introduction

PyQt

Ways of creating GUI applications

Displaying a welcome message

Understanding the Label widget

Methods

Understanding the Line Edit widget

Methods

Understanding the Push Button widget

How it works...

Using the Radio Button widget

Understanding Radio Button

Methods

Signal description

How it works...

Grouping radio buttons

Getting ready

How it works...