Python language basics 46: 2 ways to sort lists

Introduction

In the previous post we looked 3 ways to copy a list in Python: slicing, the copy function and the list constructor. We said that they all created shallow copies of the source list. Therefore beware of the implications of that if the list to be copied has mutable objects.

In this object we’ll look at 2 ways to sort the objects within a list.

Sorting

Consider the following list of cities:

cities = ["Stockholm", "Budapest", "Berlin", "Paris", "Birmingham", "Zürich"]

The ‘sort’ function operates directly on the source list and sort the elements within it:

cities.sort()

‘cities’ becomes…

[‘Berlin’, ‘Birmingham’, ‘Budapest’, ‘Paris’, ‘Stockholm’, ‘Zürich’]

…,i.e. the string elements were sorted in alphabetical order. If you want to sort the elements in descending order you can supply a keyword argument:

cities.sort(reverse=True)

[‘Zürich’, ‘Stockholm’, ‘Paris’, ‘Budapest’, ‘Birmingham’, ‘Berlin’]

If you don’t want to modify the original list but create a sorted copy then you can use the ‘sorted’ function:

sorted_cities = sorted(cities)

The ‘sorted’ function also accepts a keyword argument for descending ordering:

sorted_cities = sorted(cities, reverse=True)

‘cities’ is untouched, it still includes the same elements in the same order as before.

In the next post we’ll see 2 ways to reverse the elements in a list.

Read all Python-related posts on this blog here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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