This improvement proposal is close to : https://bugs.python.org/issue42956 and also detailed in https://stackoverflow.com/questions/13855288/turn-slice-into-range

to iterate over a slice, the recommended method seems to be : 

s = slice(5,100,3)
for i in range(s.stop)[s] :
    # do something

but if range() accepted directly a slice, it would dramatically improve the readability :

s = slice(5,100,3)
for i in range(s) :
    # do something

and it could be convenient, especially inside the __getitem__ property. I'll try to make a quick patch to test...

Accepting a slice directly in the range constructor is ambiguous. What to do if start or stop are negative or None? What if stop is less than start? You need to specify a sequence length to handle these cases.

Maybe the following expressions work for you:

   range(length)[s]

or

   range(*s.indices(length))

But other users may need different behavior (if they want convert slice(-20, -10) to range(-20, -10)). There is no general solution which would work for all, you have to code what you need.