Difference between append vs. extend list methods in Python?

Question

What's the difference between the list methods `append()` and `extend()`?

Answer 1

The key difference:

append() adds its argument as a single element to the end of the list. If you append a list, the entire list becomes one element.

extend() takes an iterable and adds each item from it individually to the list.

Examples:

If you have my_list = [1, 2, 3]

Using append([4, 5]) gives you [1, 2, 3, [4, 5]] - the list [4, 5] is added as one nested element

Using extend([4, 5]) gives you [1, 2, 3, 4, 5] - each number is added separately

Answer 2

In the extend() method you are extending the list by concatenating another list. For example

x=[1,2]

x.extend([4,5])

will result in x being [1,2,4,5]. This is the same as saying

x=[1,2]

x+=[4,5]

However, with append() you are appending the object passed as an element in the list. Therefore the code

x=[1,2]

x.append([4,5])

will result in [1,2,[4,5]]. This is because you appended a list into the first list. In summary the extend() method will extend a list by joining two lists. The append() method appends the object passed as the last element in the list. I hope that helps.