Python Lists

A list is a sequence of values. You could visualize a list as a container that holds a number of items, in a given order.

To create a list in Python, simply add any number of comma separated values between square brackets. Like this:

In Python, a list can contain items of varying data types. For example, here's a list that contains a string, an integer, and another list.

When we print both of those lists we get this:

Result
['Earth', 'Mars', 'Saturn', 'Jupiter']
['Hey', 123, ['Dog', 'Cat', 'Bird']]

Return the Number of items in a List

You can use the len() function to return the number of items in a list. Adding the len() function to the print() function will print that number out.

Accessing a List Item

You can pick out a single list item by referring to its index. Remember, Python uses zero-based indexing, so start the count at 0 when doing this.

So to find out what the second item in the planet list is, do this:

You can also select a range of items by specifying two indexes separated by a colon. Like this:

Result
['Mars', 'Saturn']

Notice that it doesn't actually include the upper index specified? I specified 1:3 but it only returned two values. This is because Python only returns the list items up to, but not including, the last index specified.

Negative Indexing

You can use a negative index to start counting from the end of the list. In this case, the count starts at -1 (not zero). So an index of -1 is the last item, -2 is the second last item, and so on.

Example:

Result
Saturn

Update a List Item

You can change a list item like this:

So it's like setting a variable, but appending the variable name with the list item's index inside square brackets.

Here's a demonstration:

Result
['Earth', 'Mars', 'Saturn', 'Jupiter']
['Earth', 'Mercury', 'Saturn', 'Jupiter']

Append a List Item

You can add items to a list by using the append() function. Here's an example:

Here's a demonstration:

Result
['Earth', 'Mars', 'Saturn', 'Jupiter']
['Earth', 'Mars', 'Saturn', 'Jupiter', 'Mercury']

Delete a List Item

Use the del keyword to delete a list item at a particular index. Like this:

Here's a demonstration:

Result
['Earth', 'Mars', 'Saturn', 'Jupiter']
['Earth', 'Mars', 'Jupiter']