Lists and Tuples

Introduction

One variable holds one value. But what if you have a shopping list, or the scores of thirty students? A list holds many values in order, in one variable.

Creating and reading lists

Write a list in square brackets, separated by commas. Items are numbered from 0, just like characters in a string.

A list can hold anything, even a mix of types, and other lists:

Changing a list

Unlike strings, lists can be changed.

Searching, counting and sorting

sorted(x) returns a new list and leaves the original alone. x.sort() changes the list in place and returns nothing. Beginners often mix these up.

Looping over lists

Lists are shared, not copied

When you assign a list to another name, both names point to the same list.

Use .copy() or list(a) when you need an independent copy.

Tuples

A tuple is like a list that cannot be changed. Use round brackets. Tuples are good for values that belong together and should stay fixed, such as coordinates.

You can unpack a tuple (or list) into separate variables in one line:

Try it yourself

Given the list of test scores below, print the highest score, the lowest score, the average (rounded to 1 decimal place) and the scores in order from high to low.

Summary

• A list is an ordered, changeable collection in square brackets, indexed from 0.
• Use append, insert, remove, pop and del to change lists, and sorted() or .sort() to order them.
• Loop with for item in items, or enumerate for index and value. Assigning a list does not copy it: use .copy().
• A tuple ( , ) cannot be changed, and unpacking splits it into variables.