1.35 Itse1359-1130-unpacking tuples

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Introduction
• What is a tuple?
• Sample program
  • Program to unpack a tuple
  • Tuples can be concatenated
  • Unusual syntax
  • Packing and unpacking a tuple
  • Unpack the tuple into the mutable list
• Complete program listing
• Visualization of the tuples in the program
• Run the program
• Miscellaneous

Preface

This module is one in a collection of modules on Python designed for teaching ITSE 1359 Introduction to Scripting Languages: Python at Austin Community College in Austin, TX.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.

(Note to blind and visually impaired students: most of the Figures and all of the Listings inthis module are presented in plain text format and should be accessible using an audio screen reader or a braille display.)

Figures

• Figure 1 . Output from the code in Listing 1.
• Figure 2 . Output from the code in Listing 2.
• Figure 3 . Output from the code in Listing 3.
• Figure 4 . Output from the code in Listing 4.
• Figure 5 . Visualization of the tuples in the program.
• Figure 6 . Output from the modified program.

Listings

• Listing 1 . Beginning of the program.
• Listing 2 . Unpack the tuple and print individual elements.
• Listing 3 . Unpack the tuple into the mutable list.
• Listing 4 . Complete program listing.

Introduction

This module is part of a series of modules designed to teach you about tuples.

Earlier modules have illustrated

• How to create (pack) a tuple.
• How to access a tuple item using indexing.
• How to slice a tuple.
• How to nest tuples.
• How to create empty tuples.
• How to create single-item tuples.

This module will teach you about unpacking tuples.

What is a tuple ?

A tuple is an immutable ordered list of objects. It can contain references to any type of object. See earlier modules in this series for a more detaileddescription.

Sample program

Program to unpack a tuple

Listing 4 presents a Python program that:

• Creates (packs) two simple tuples.
• Creates (packs) a third tuple by concatenating the first two tuples.
• Displays the third tuple.
• Unpacks the third tuple, assigning each item of the tuple into a separate variable.
• Displays each of the variables.
• Creates and displays a mutable list object containing five strings.
• Unpacks the tuple created earlier assigning the four items from the tuple into the first four items in the list.
• Displays the list.

Figure 4 shows the output produced by the program in Listing 4 .

Figure 5 shows a visualization of the tuples in the program after the first five statements in the code block have been executed.This is a case where you need to step through the program and observe changes in the diagram on the right to appreciate the behavior of the program.

I will explain this program in fragments. Listing 1 shows the beginning of the program.