The extend() method adds all elements from an iterable to the end of a list. Unlike append(), which adds one item, extend() unpacks the iterable.
Given fruits = ["apple"], calling fruits.extend(["banana", "cherry"]) results in ["apple", "banana", "cherry"]. Three separate elements, not a nested list. You can extend with any iterable: letters = ["a", "b"] then letters.extend("cd") gives ["a", "b", "c", "d"] since strings are iterable.
Like append(), extend() modifies in place and returns None. Choose extend() when combining lists or adding multiple items at once.