Python

List Methods

Built-in methods that make lists easier to work with

List Methods Overview

In Python, there are several built-in functions that work on lists and make our life much easier. Here are some of the basics.

.append()

The .append() function allows us to add a new item to a list. It follows the format "list_name.append(new_item)". For example…

rainbow_colors = ["violet", "indigo", "blue", "green", "yellow", "orange", "red"]
rainbow_colors.append("black")
print(rainbow_colors)

Output:

["violet", "indigo", "blue", "green", "yellow", "orange", "red", "black"]

We added the color "black" to the list using the .append() function.

len()

This built-in function allows us to access the length of the list. It becomes especially useful when we need to know the number of entries in a list for programs that work with lists of items. Here’s an example…

rainbow_colors = ["violet", "indigo", "blue", "green", "yellow", "orange", "red"]
print(len(rainbow_colors))

Output:

7

.sort()

The .sort() function can be used to sort a list in ascending or descending order. Here’s how…

rainbow_colors = ["violet", "indigo", "blue", "green", "yellow", "orange", "red"]
rainbow_colors.sort()
print("Ascending order: " + str(rainbow_colors))
rainbow_colors.sort(reverse=True)
print("Descending order: " + str(rainbow_colors))

Output:

Ascending order: ['blue', 'green', 'indigo', 'orange', 'red', 'violet', 'yellow']
Descending order: ['yellow', 'violet', 'red', 'orange', 'indigo', 'green', 'blue']

Here we have sorted the list in both ascending and descending order. The default of .sort() is ascending order. To set it to descending order, set the ‘reverse’ parameter of the .sort() argument to ‘True’. This built-in method can come in handy when you need to sort lists by an id number, or you want to sort by value (like shopping websites do with prices listed low to high or high to low).

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