This book expects that you know the basics of Python 3. You should know how to write and run simple scripts using built-in types and functions, how to define your own functions and classes, and how to import modules from the standard library.

You can follow this book if you run Windows, macOS, Linux, or even BSD. Ensure that you have Python 3 and Tcl/Tk installed (Chapter 1, Introduction to Tkinter, contains instructions for Windows, macOS, and Linux) and that you have an editing environment with which you are comfortable (we suggest IDLE since it comes with Python and uses Tkinter). In the later chapters, you'll need access to the internet so that you can install Python packages and the PostgreSQL database.

You can download the example code files for this book from your account at www.packtpub.com. If you purchased this book elsewhere, you can visit www.packtpub.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

1. Log in or register at www.packtpub.com.
2. Select the SUPPORT tab.
3. Click on Code Downloads & Errata.
4. Enter the name of the book in the Search box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

• WinRAR/7-Zip for Windows
• Zipeg/iZip/UnRarX for Mac
• 7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Python-GUI-Programming-with-Tkinter. In case there's an update to the code, it will be updated on the existing GitHub repository.

We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Determine the appropriate input widget for each data field."

A block of code is set as follows:

def has_five_or_less_chars(string):
    return len(string) <= 5

    wrapped_function = root.register(has_five_or_less_chars)
    vcmd = (wrapped_function, '%P')
    five_char_input = ttk.Entry(root, validate='key', validatecommand=vcmd)

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

[default]
exten => s,1,Dial(Zap/1|30)
exten => s,2,Voicemail(u100)
exten => s,102,Voicemail(b100)
exten => i,1,Voicemail(s0)

Any command-line input or output is written as follows:

pip install --user psycopg2-binary

Bold: Indicates a new term, an important word, or words that you see onscreen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "Once installed, launch pgAdmin and create a new admin user for yourself by selecting Object | Create | Login/Group Role."