refactoring maps code on set comprehension

[ArtemIsmagilov]

1. bytecode faster
2. the code is easier
3. speed finding elements in set O (1) (hashable elemets)

[tobixen]

Seems good to use set rather than list, but I will have to review this one a bit more carefully.

[ArtemIsmagilov]

look example

print(' sa asd asd\r\n \f \t dad as as , asd'.split())
['sa', 'asd', 'asd', 'dad', 'as', 'as', ',', 'asd']

[ArtemIsmagilov]

This method is used only in 2 places to search for a string, set is suitable here. Map, filter and lambda are unnecessary here. For library users, nothing should change.