Algorithmic complexity of len (list)?

[Tim Peters]

[Roy Smith]
> Is the length of a list stored in the object, or does len() have to
> count the elements each time you call it?  In other words, is len (list)
> O(1) or O(n)?

O(1).  Ditto len(tuple), len(dict), len(str), len(unicode), and
len(array.array).