List Joins

3.4. List Joins#

When we print lists they’ll be displayed using square brackets with list items separated by commas.

todo = ["Buy carrots", "Wash car", "Study for quiz"]
print(todo)

Sometimes we want to display list items differently. To help us, we can use the .join() method. This allows us to join all the elements in a list together with a specified separator.

Here is the syntax for joining:

separator.join(list)

Here is an example where we use the separator ', ' ( a comma followed by a space).

todo = ['Buy carrots', 'Wash car', 'Study for quiz']
print(', '.join(todo))

Buy carrots, Wash car, Study for quiz

You’ll notice that the separate only goes between list items and doesn’t appear at the start or at the end.

Here is another example where use use '\n' (a newline character).

todo = ['Buy carrots', 'Wash car', 'Study for quiz']
print('\n'.join(todo))

Buy carrots
Wash car
Study for quiz

Note that .join() can only be used on lists containing strings. The following will result in an error since the list elements are integers.

numbers = [7, 4, -1, 3]
print(", ".join(numbers))

Traceback (most recent call last):
        File "/home/main.py", line 2, in <module>
                print(', '.join(numbers))
                                        ^^^^^^^^^^^^^^^^^^
TypeError: sequence item 0: expected str instance, int found