The <len> block is equivalent to the “len()” function in Python; it counts the number of elements in the input “in.”
See the Python documentation for more details.
•« in » : The variable for which you want to know the number of elements
•« len(in) » : The number of elements (items) in the “in” variable
The input can be of any type, but the most relevant types are: list, str, tuple.
The output is of type int.