What function is used to count the number of items in a list?

The function used to count the number of items in a list is len(). This built-in Python function returns the total number of elements contained in the iterable passed to it, such as a list, string, tuple, or dictionary. For example, calling len(my_list) will provide the count of items present in my_list.

Using len() is essential for situations where understanding the size of a collection is necessary, such as iterating over the collection, allocating resources, or verifying the completion of operations that modify the length of the list.

The other functions listed serve different purposes: max() finds the maximum value in an iterable, sum() calculates the total of numerical values in an iterable, and sorted() returns a new sorted list from the elements of any iterable. Each of these serves a unique function and does not pertain to counting items within a list.