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Raspberry Pi Cookbook, 4th Edition
book

Raspberry Pi Cookbook, 4th Edition

by Simon Monk
December 2022
Beginner to intermediate content levelBeginner to intermediate
618 pages
12h 41m
English
O'Reilly Media, Inc.
Book available
Content preview from Raspberry Pi Cookbook, 4th Edition

Chapter 6. Python Lists and Dictionaries

6.0 Introduction

In Chapter 5, we looked at the basics of the Python language. In this chapter, we will look at two key Python data structures: lists and dictionaries.

6.1 Creating a List

Problem

You want to use a variable to hold a series of values rather than just one value.

Solution

Use a list. In Python, a list is a collection of values stored in a specific order so that you can access them by position.

You create a list by using the [ and ] characters to contain its initial contents:

>>> a = [34, 'Fred', 12, False, 72.3]
>>>

Unlike the more rigid arrays in languages like C, you don’t need to specify the size of a list in Python when you declare it. You can also change the number of elements in the list any time you like.

Discussion

As this example illustrates, the items in a list do not need to be the same type, although they often are. In fact its quite common for the elements of a list to themselves be lists.

To create an empty list that you can add items to later, you can use:

>>> a = []
>>>

6.2 Accessing Elements of a List

Problem

You want to find individual elements of a list or change them.

Solution

Use the [] notation to access elements of a list by their position in the list. For example, to access the element at position 1 in a list:

>>> a = [34, 'Fred', 12, False, 72.3]
>>> a[1]
'Fred'

Discussion

The list positions (indices) start at 0 for the first element (not at 1).

As well as using the [] notation to ...

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Publisher Resources

ISBN: 9781098130916Errata PageSupplemental Content