Use 'for' loops with lists

  • 5 minutes

In Python, lists can store any type of value, such as strings or numbers:

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]

You can access any item in a list by enclosing the index in brackets ([]) after the variable name. Indexes start from 0:

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]

print("The first planet is ", planets[0])
print("The second planet is ", planets[1])
print("The third planet is ", planets[2])

You can also determine the number of items in a list by using len. So you could use a while loop and a counter to loop or iterate over each item in the list. Because this operation is so common, Python provides for loops, which you can use to iterate over lists.

Note

Python has many types that can be looped over. These types are known as iterables.

Python lists are iterable, and they can be used with a for loop. You use a for loop with iterables where you loop a known number of times, once for each item in the iterable.

About for loops

Here's an example for loop that counts down from 4 to 0:

countdown = [4, 3, 2, 1, 0]
for number in countdown:
    print(number)
print("Blast off!! 🚀")

The for loop is a statement with five important parts:

  • The word for, followed by a space.
  • The variable name you want to create for each value in the sequence (number). Note multiple variables need to be separated by commas.
  • The word in, surrounded by spaces.
  • The name of the list (countdown, in the preceding example), or iterable that you want to loop over, followed by a colon (:).
  • The code you want to run for each item in the iterable, separated by nested whitespace.

Let's change that code to wait for one second between each number by using the sleep() function:

from time import sleep

countdown = [4, 3, 2, 1, 0]

for number in countdown:
    print(number)
    sleep(1)  # Wait 1 second
print("Blast off!! 🚀")

Note

Most Python code uses four spaces as the unit of whitespace. To save having to press the space bar four times, most editors have a Tab key shortcut that inserts four spaces.