These represent finite ordered sets indexed by non-negative numbers. The built-in function
len() returns the number of items of a sequence. When the length of a sequence is
n , the index set contains the numbers
0, 1, ..., n-1 . Item
i of sequence a is selected by
a<a href='https://docs.python.org/3/reference/datamodel.html#the-standard-type-hierarchy' target='_blank' rel='nofollow'>i] .
[Python Docs - Standard Type Hierarchy