A quick tutorial for the for/else construct in Python

In a Python course, you learned that you use an else statement when you use an if statement:

if condition:
    # Do stuff
else:
    # Do stuff given condition failed

But, you can also use the else statement in conjunction with a for loop, which allows you to signify that a loop was never broken out of with a break statement:

items = ['apple', 'banana', 'cherry', 'date']
search_item = 'orange'

for item in items:
    if item == search_item:
        print(f"Found {search_item}!")
        break
else:
    print(f"{search_item} not found in the list.")

How for/else works

The else block in a for/else loop is executed only if the loop completes all its iterations without encountering a break statement. If the loop is interrupted by a break statement, the else block is skipped.

In the code snippet above, we search for the word “orange” in the items list. If we find it, we print a success message and exit the loop with break.

However, if the loop completes without finding “orange”, the else block runs, printing a message that the item was not found.

The purpose of for/else

Going back to the semi-early days of your Python learning, you learned about control flow. This was referring to looping (for/while) and if/elif/else statements.

However, this construct was likely left out for a number of reasons:

1. It’s an unconventional way to write Python code,

2. This construct is not found in any other languages,

3. There’s very limited use cases.

Key usage: Use a for/else loop to define behavior after you are done looping if you don’t break out of the loop.

Copy/pasting the code from above for reference:

items = ['apple', 'banana', 'cherry', 'date']
search_item = 'orange'

for item in items:
    if item == search_item:
        print(f"Found {search_item}!")
        break
else:
    print(f"{search_item} not found in the list.")

We want to find the word orange in the items list above. If we successfully find this, then we’ll print out a success message and break out of the loop.

However, if we’re unsuccessful in finding the word orange in the list, then we’ll execute the else statement, saying we didn’t find it.

Another Way to Write the Code

Instead of using a for/else statement, we could stick with an if/else statement outside of the for loop. We’d have to include a boolean to keep track of whether we found the item or not:

items = ['apple', 'banana', 'cherry', 'date']
search_item = 'orange'
item_found = False # assume it hasn't been found

for item in items:
    if item == search_item:
        item_found = True
        break

if item_found:
    print(f"Found {search_item}!")
else:
    print(f"{search_item} not found in the list.")

Both constructs that are shown here are valid ways of writing code. This way is more straight-forward and forces us to think in a more logical manner.

At the end of the day, it’s up to you how you want to handle something like this. I think that the for/else statement is slightly more elegant, as we don’t need to have another variable introduced in our code.