What does the 'len()' function do in Python?

The 'len()' function in Python is used to find the length of a sequence, which includes data types such as lists, strings, tuples, and dictionaries. When applied to a string, 'len()' returns the number of characters in that string. For a list, it returns the number of elements present in that list. This functionality is crucial for many programming tasks, such as iterating over elements, validating input, or adjusting data structures dynamically based on their size.

Using 'len()' provides a straightforward way to assess how many items are present in a data structure, making it an essential tool in Python programming for manipulating and understanding collections of data.