In Python, what does the len() function do?

The len() function in Python is designed to return the number of items in a collection, such as a list. When it is applied to a list, it counts the total number of elements contained in that list and returns this count as an integer. This functionality is fundamental for understanding how to work with data structures in Python, as knowing the length of a list can be crucial for various operations, such as iterating through the list or validating its contents.

For instance, if you have a list defined as my_list = [1, 2, 3, 4], using len(my_list) would return 4, signifying that there are four elements in the list. This capability extends beyond lists and can also be applied to other iterable types, including strings and tuples, making it a versatile function in Python programming.