Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Python Introducing Lists Meet Lists Addition

What's the difference between append and extend in this example?

I don't understand what differentiates append and extend. Is it that append is for one item as a string and extend is for adding multiple items?

Dave StSomeWhere
Dave StSomeWhere
19,870 Points

It is possible that if you try experimenting in your REPL you might get a better understanding of the difference between the two methods.

Something like below could be a good start:

list1 = ['a', 'b', 'c']
list2 = ['d','e', 'f']
list3 = [1, 2, 3]
str1 = "String Example"
dict1 = {'name':'dict one', 'type':'sample'}
dict2 = {'name':'dict two', 'type':'another sample'}
list1.append(list2)
list1
['a', 'b', 'c', ['d', 'e', 'f']]
list1.extend(list3)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3]
list1.extend(dict1)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3, 'name', 'type']
list1.append(dict2)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3, 'name', 'type', {'name': 'dict two', 'type': 'another sample'}]

2 Answers

Steven Parker
Steven Parker
230,024 Points

The "append" method adds a single item to a list, though the item might be another list. On the other hand, "extend" will add another list as individual items. You can see this in the example you provided:

list1.append(list2)
list1
['a', 'b', 'c', ['d', 'e', 'f']]           # list2 is still a list, INSIDE the big list
list1.extend(list3)
list1
['a', 'b', 'c', ['d', 'e', 'f'], 1, 2, 3]  # but 1, 2, and 3 are separate in the big list

Happy coding! :christmas_tree: And for some holiday-season fun and coding practice, give Advent of Code a try! :santa:

Was just about to ask the same question and found your answer. Many thanks.

if one can extend a list with single list item, why bother with append?

Steven Parker
Steven Parker
230,024 Points

You might want to add something to a list that isn't already in another list.