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

The output of the len() function when applied to an empty list is 0. In Python, the len() function is designed to return the number of items in an object. When it comes to lists, this means counting how many elements are present. An empty list, denoted by [], contains no elements, hence its length is 0.

This function behaves consistently across different data types, including lists, strings, dictionaries, and more, always providing a count of current elements or items within that structure. Since an empty list has no elements, invoking len() on it naturally results in a return value of 0.

In contrast, the other options present incorrect scenarios: a length of 1 would suggest there is at least one element in the list, while an error at runtime does not occur since an empty list is still a valid object type in Python. Returning None would imply the absence of a value, but len() specifically produces an integer output representing the count, which in this case is zero.