What is the output of the function len() when applied to an empty list?

The function len() in Python is used to determine the number of items in an object, such as a list, string, or dictionary. When applied to an empty list, the len() function returns 0 because there are no elements contained within the list. This behavior is consistent across all list types in Python—whether the list is completely empty or populated with elements, len() accurately counts the number of items present.

Therefore, when you apply len() to an empty list specifically, you are checking how many elements it holds, and since there are none, the return value is indeed 0. This foundational understanding of the len() function is essential for managing and manipulating collections in Python.