Sorry, but I couldn't get it. :(

I don't get the idea of the three iter(s) refering to the same position in s (or do they?). They should refer to different positions in order to give the desired output.

You say

zip(*[iter(s)]*3)=zip(iter(s),iter(s),iter(s))

which is not true. The code (where s='abcdefghi'):

for part in zip(iter(s),iter(s),iter(s)):
    print(part)

gives output:

('a', 'a', 'a')
('b', 'b', 'b')
('c', 'c', 'c')
('d', 'd', 'd')
('e', 'e', 'e')
('f', 'f', 'f')
('g', 'g', 'g')
('h', 'h', 'h')
('i', 'i', 'i')

This output makes sense because each iter(s) refers to the same position in s for each iteration of the for loop.

Could you please clear my doubt?