Cost of len() function

Calling len() on those data types is O(1) in CPython, the official and most common implementation of the Python language. Here's a link to a table that provides the algorithmic complexity of many different functions in CPython:

TimeComplexity Python Wiki Page

It's O(1) (constant time, not depending of actual length of the element - very fast) on every type you've mentioned, plus set and others such as array.array.