Tkinter GUI application development cookbook packt publishing (2018)

Tkinter GUI Application Development Cookbook Tkinter GUI Application Development Cookbook A practical solution to your GUI development problems with Python and Tkinter Alejandro Rodas de Paz BIRMINGHAM MUMBAI Tkinter GUI Application Development Cookbook Copyright © 2018 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 b.

A practical solution to your GUI development problems withPython and Tkinter

Development Cookbook

Copyright © 2018 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

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Contributors

Alejandro Rodas de Paz is a computer engineer from Seville,

Spain He has developed several projects with Python, from webcrawlers to artificial intelligence algorithms He has also used

Javier Becerra Elcinto received his PhD in image processing

from the Université de Bordeaux in 2006 In 2010 he started

working as a self-employed developer working with Python andC++, and in 2014 he cofounded Panoimagen S.L There, he hascontinued to develop software for industrial and precision

agriculture applications Javier lectures regularly on scientific

programming in private companies and several Spanish researchinstitutions

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As one of the more versatile programming languages, Python is wellknown for its batteries-included philosophy, which includes a richset of modules in its standard library; Tkinter is the library used tobuild desktop applications Built over the Tk GUI toolkit, Tkinter is

a common choice for rapid GUI development, and complex

applications can benefit from the full capabilities of this library.This book covers all of your Tkinter and Python GUI developmentproblems and solutions

Tkinter GUI Application Development Cookbook starts with an

overview of Tkinter classes and at the same time provides recipesfor basic topics, such as layout patterns and event handling Next,this book covers how to develop common GUI patterns, such asentering and saving data, navigating through menus and dialogs,and performing long-running actions in the background You canthen make your apps leverage network resources effectively andperform graphical operations on a canvas and related tasks such asdetecting collisions between items Finally, this book covers usingthemed widgets, an extension of Tk widgets that have a more nativelook and feel

By the end of the book, you will have an in-depth knowledge of

Tkinter classes and know how to use them to build efficient and richGUI applications

This book targets Python developers who are familiar with thebasics of the language—syntax, data structures, and OOP—wants tolearn effective solutions to the common challenges of GUI

development, and desires to discover interesting capabilities thatTkinter can offer to build complex applications

You do not need previous experience with Tkinter or other GUIdevelopment libraries since the first part of the book will teach thebasics of the library through the introductory use cases

Chapter 1, Getting Started with Tkinter, introduces the structure of a

Tkinter program and shows you how to perform the most commontasks, such as creating widgets and handling user events

Chapter 7, Canvas and Graphics, explores the Canvas widget and the

types of items you can add to the canvas and how to manipulatethem

Chapter 8, Themed Widgets, teaches you how to extend Tkinter

applications with the Tk-themed widget set

To get the most out of this book

To get up and running, users will need to have the followingtechnologies installed:

Python 3.x

Any operating system

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Thanks to its clear syntax and the wide ecosystem of libraries andtools, Python has become a popular and general-purpose

programming language From web development to Natural

Language Processing (NLP), you can easily find an open source

library that fits the need of your application domain, and in the lastinstance, you can always use any of the modules included in thePython standard library

The standard library follows the "batteries-included" philosophy,which means that it contains a large collection of utilities: regularexpressions, mathematical functions, networking, and so on The

standard Graphical User Interface (GUI) package of this library

is Tkinter, a thin object-oriented layer on top of Tcl/Tk.

Starting from Python 3, the Tkinter module was renamed to tkinter

(with a lowercase t) It also affects to the tkinter.ttk and tkinter.tix

extensions We will dive into the tkinter.ttk module in the last

chapter of this book, since the tkinter.tix module is officially

deprecated

In this chapter, we will explore several patterns for some basic

classes of the tkinter module and some methods that are common toall widget subclasses

application

One of the main advantages of making applications with Tkinter isthat it is very easy to set up a basic GUI with a script of a few lines

As the programs get more complex, it becomes more difficult toseparate logically each part, so an organized structure will help us tokeep our code clean

expected However, all our variables are defined in the global

namespace, and the more widgets you add, the more difficult itbecomes to reason about the parts where they are used

Wildcard imports ( from import * ) are strongly discouraged in production code because they pollute your global namespace—we only used them here to illustrate an anti-pattern that can be commonly seen in online examples.

These maintainability issues can be addressed with basic OOPtechniques, which are considered good practice in all types ofPython programs

To improve the modularity of our simple program, we will define aclass that wraps our global variables:

We will follow this convention through all the code samples, so youcan take this template as the starting point of any larger application.

We subclassed the Tk class in our example, but it is also common tosubclass other widget classes We did this to reproduce the samestatements that we had before we refactored the code

However, it may be more convenient to subclass Frame or Toplevel inlarger programs, such as those with multiple windows This is

because a Tkinter application should have only one Tk instance, andthe system creates one automatically if you instantiate a widgetbefore you create the Tk instance

Keep in mind that this decision does not affect the structure of our

App class since all widget classes have a mainloop method that

internally starts the Tk main loop

Button widgets represent a clickable item of your GUI applications.They typically use a text or an image indicating the action that will

be performed when clicked Tkinter allows you to easily configurethis functionality with some standard options of the Button widgetclass

The following contains a button with an image that gets disabledwhen clicked and a list of buttons with the different types ofavailable reliefs:

After executing the preceding code, you will get the followingoutput:

The most basic way of instantiation of Button is using the text option

to set the button label and the command option that references thefunction to be invoked when the button is clicked

In out example, we also added PhotoImage via the image option, which

takes precedence over the text string The compound option serves tocombine image and text in the same button, determining the

position where the image is placed It accepts the following

constants as valid values: CENTER, BOTTOM, LEFT, RIGHT, and TOP

The second row of buttons is created with a list comprehension,using the list of RELIEF values The label of each button corresponds

to the name of the constant, so you can note the difference in theappearance of each button

We used an attribute to keep a reference to our PhotoImage instance,even though we are not using it outside our init method Thereason is that images are cleared when they are garbage collected,which will happen if we declare it as a local variable and the methodexists

To avoid this, always remember to keep a reference to each PhotoImage

object as long as the window where it is shown is still alive

The Entry widget represents a text input displayed in a single line.Along with the Label and Button classes, it is one of the most

commonly used Tkinter classes

The Entry widgets are instantiated using the parent window orframe as the first argument and a set of optional keyword

arguments to configure additional options We did not specify anyoptions for the entry corresponding to the username field To keep thepassword secret, we specify the show argument with the string "*",which will display each typed character as an asterisk

With the get() method, we will retrieve the current text as a string.This is used in the print_login method to show the entries' content inthe standard output

The delete() method takes two arguments that indicate the range ofthe characters that should be deleted Keep in mind that the indicesstart at the position 0, and they do not include the character at theend of the range If only one argument is passed, it deletes the

character at that position

In the clear_form() method, we delete from index 0 to the constant END,which means that the whole content is removed Finally, we set thefocus to the username entry

The content of an Entry widget can be modified programmaticallywith the insert() method, which takes two arguments:

index: The position to insert the text; note that entry positionsare 0-indexed

string: The text to insert

A common pattern to reset the content of an entry with a defaultvalue can be achieved with a combination of delete() and insert():

entry.delete(0, tk.END)

entry.insert(0, "default value")

Another pattern is to append the text in the current position of thetext cursor Here, you can use the INSERT constant instead of having

The Tracing text changes recipe The Validating a text entry recipe

Tk variables allow your applications to get notified when an inputchanges its value There are four variable classes in Tkinter: BooleanVar,

DoubleVar, IntVar, and StringVar Each one wraps the value of the

corresponding Python type, which should match the type of theinput widget attached to the variable

This feature is particularly useful if you want to automatically

update certain parts of your application based on the current state

of some input widgets