Python GUI Programming with Tkinter Second Edition Design and build functional and user-friendly GUI applications Alan D. Moore BIRMINGHAM—MUMBAI Python GUI Programming with Tkinter Second Edition Copyright © 2021 Packt Publishing 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. Producer: Tushar Gupta Acquisition Editor – Peer Reviews: Suresh Jain Project Editor: Namrata Katare Content Development Editor: Lucy Wan Copy Editor: Safis Editing Technical Editor: Karan Sonawane Proofreader: Safis Editing Indexer: Subalakshmi Govindhan Presentation Designer: Ganesh Bhadwalkar First published: May 2018 Second edition: October 2021 Production reference: 1261021 Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK. ISBN 978-1-80181-592-5 www.packt.com Contributors About the author Alan D. Moore has been coding in Python since 2005. He lives in Franklin, Tennessee, where he develops database apps for the local government. His technical interests include Python, JavaScript, Linux, and analog electronics. In his free time, he publishes coding videos on the YouTube channel Alan D Moore Codes, makes music, builds guitar effects, volunteers at his church and scout troop, and helps his wife raise their five children. Profound thanks to Lucy and Alejandro, without whom this book would be riddled with errors; to Cara and the kids for their support and encouragement; and to the Python and Tcl/Tk communities for providing such great software. God bless you all! About the reviewer Alejandro Rodas de Paz is a computer engineer from Seville, Spain. He has developed several professional and academic Python projects, from artificial intelligence algorithms to DevOps scripting. Prior to this publication, Alejandro wrote the Packt titles Python Game Development by Example and Tkinter GUI Application Development Cookbook. He also collaborated as a technical reviewer on the book Tkinter GUI Application Development Hotshot. I would like to thank and dedicate this work to my sister Belen, whose next year will be the beginning of a long and joyful journey. Wish you all the best on this next chapter of life. Table of Contents Preface xvii Chapter 1: Introduction to Tkinter 1 Introducing Tkinter and Tk 2 Choosing Tkinter 2 Installing Tkinter 3 Installing Python 3.9 on Windows 3 Installing Python 3 on macOS 4 Installing Python 3 and Tkinter on Linux 4 Introducing IDLE 4 Using the shell mode of IDLE 5 Using the editor mode of IDLE 5 IDLE as a Tkinter example 6 Creating a Tkinter Hello World 7 An overview of basic Tkinter 9 Building a GUI with Tkinter widgets 10 Arranging our widgets with geometry managers 14 Making the form actually do something 19 Handling data with Tkinter control variables 21 Using control variables in a callback function 26 The importance of control variables 28 Summary 28 Chapter 2: Designing GUI Applications 29 Analyzing a problem at ABQ AgriLabs 29 Assessing the problem 30 Gathering information about the problem 30 Interviewing the interested parties 31 Analyzing what we've found out 33 Information from the data originators 34 [ v ] Table of Contents Information from the users of the application 35 Information from technical support 36 Information from the data consumer 36 Documenting specification requirements 37 Contents of a simple specification 38 Writing the ABQ data entry program specification 39 Designing the application 42 Deciding on input widgets 42 Grouping our fields 44 Laying out the form 45 Laying out the application 47 Evaluating technology options 49 Summary 50 Chapter 3: Creating Basic Forms with Tkinter and Ttk Widgets 51 The Ttk widget set 51 The Label widget 52 The Entry widget 53 The Spinbox widget 54 The Checkbutton widget 56 The Radiobutton widget 57 The Combobox widget 58 The Text widget 59 Text widget indices 60 The Button widget 62 The LabelFrame widget 62 Implementing the application 64 First steps 65 Building the data record form 66 The Record Information section 67 The Environment Data section 69 The Plant Data section 70 Finishing the GUI 72 Writing the callback functions 73 The Reset function 73 The Save callback 74 Finishing up and testing 78 Summary 79 Chapter 4: Organizing Our Code with Classes 81 A primer on Python classes 81 The advantages of using classes 82 Classes are an integral part of Python 82 Classes make relationships between data and functions explicit 82 [ vi ] Table of Contents Classes help create reusable code 83 Syntax of class creation 83 Attributes and methods 83 Magic attributes and methods 86 Public, private, and protected members 88 Inheritance and subclasses 90 Using classes with Tkinter 91 Improving Tkinter classes 91 Creating compound widgets 93 Building encapsulated components 95 Subclassing Tk 97 Rewriting our application using classes 100 Adding a StringVar to the Text widget 100 Passing in a variable 101 Synchronizing the widget to the variable 101 Synchronizing the variable to the widget 102 Creating a more advanced LabelInput() 103 Creating a form class 106 Creating an application class 112 Summary 114 Chapter 5: Reducing User Error with Validation and Automation 117 Validating user input 117 Strategies to prevent data errors 118 Validation in Tkinter 119 The validate argument 120 The validatecommand argument 120 The invalidcommand argument 122 Creating validated widget classes 123 Creating a Date field 125 Implementing validated widgets in our GUI 129 Introducing the power of multiple inheritance 129 Building a validating mixin class 132 Building validating input widgets with ValidatedMixin 136 Requiring data 136 Creating a Date widget 137 A better Combobox widget 138 A range-limited Spinbox widget 140 Validating Radiobutton widgets 144 Updating our form with validated widgets 146 Implementing validation interaction between form widgets 149 Dynamically updating the Spinbox range 149 Dynamic disabling of fields 154 Displaying errors 156 Preventing form submission on error 157 [ vii ] Table of Contents Automating input 159 Date automation 160 Automating Plot, Lab, Time, and Technician 161 Summary 162 Chapter 6: Planning for the Expansion of Our Application 163 Separating concerns 164 The MVC pattern 164 What is a model? 165 What is a view? 165 What is a controller? 166 Why complicate our design? 166 Structuring our application directory 167 Basic directory structure 167 The abq_data_entry.py file 168 The README.rst file 169 Populating the docs folder 170 Making a Python package 170 Splitting our application into multiple files 172 Creating the models module 172 Moving the widgets 179 Moving the views 180 Removing redundancy in our view logic 181 Using custom events to remove tight coupling 185 Creating the application file 186 Running the application 188 Using version control software 189 A super-quick guide to using Git 189 Initializing and configuring a Git repository 190 Adding and committing code 190 Viewing and using our commits 191 Summary 192 Chapter 7: Creating Menus with Menu and Tkinter Dialogs 193 Solving problems in our application 194 Planning solutions to the issues 194 Implementing Tkinter dialogs 196 Error dialogs with the Tkinter messagebox 196 Showing error dialogs in ABQ Data Entry 199 Using filedialog 201 Using simpledialog and creating a custom dialog 204 Creating a Login dialog using simpledialog 205 Incorporating the LoginDialog in our class 208 Designing the application menu 211 The Tkinter Menu widget 211 [ viii ] Table of Contents Using Checkbutton and Radiobutton items 213 Implementing the ABQ application menu 215 Adding a Help menu 216 Adding a File menu 217 Adding a settings menu 220 Finishing the menu 222 Persisting settings 223 Building a model for settings persistence 224 Using the settings model in our application 228 Summary 230 Chapter 8: Navigating Records with Treeview and Notebook 231 Implementing read and update in the model 231 Adding read and update to the CSVModel class 232 Implementing get_all_records() 233 Implementing get_record() 235 Adding update capability to save_record() 236 The Ttk Treeview 237 Anatomy of a Treeview 238 Building a file browser 239 Creating and configuring a Treeview 240 Populating a Treeview with data 242 Sorting Treeview records 244 Using Treeview virtual events 247 Implementing a record list with Treeview 248 Creating the RecordList class 249 Configuring a Treeview widget 250 Adding a scrollbar for the Treeview 252 Populating the Treeview 253 Adding the record list to the application 254 Modifying the record form for read and update 255 Adding a current record property 255 Adding a label to show what is being edited 255 Adding a load_record() method 256 Updating the application layout 257 The Ttk Notebook widget 259 Adding a notebook to our application 261 Adding and updating application callbacks 262 The _show_recordlist() method 263 The _populate_recordlist() method 264 The _new_record() method 265 The _open_record() method 266 The _on_save() method 267 Main menu changes 267 Testing our program 268 Summary 269 [ ix ]