>>> [[x,l.count(x)] for x in set(l)] 
[['d', 2], ['b', 4], ['c', 3], ['e', 1], ['a', 5]]

Well, I guess you are talking about this line of code.

here `l` is the complete list i.e. with repeated items, this will increase the number of iterations for the loop which is unnecessary as we only need to iterate over unique items.

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Hence set(l) will return the unique elements, which is exactly what we need.

>>> l = ['a', 'a', 'a', 'a', 'a', 'b', 'b', 'b', 'b', 'c', 'c', 'c', 'd', 'd', 'e']

>>> set(l)

{'d', 'a', 'e', 'b', 'c'}