Given a python slice object and a given length, return a range representing the indices that should be returned for that slice for a collection of that length (useful for implementing __getitem__ for slice as index)

range_from_slice.py

def range_from_slice_overcomplicated(slc: slice, length: int) -> range:
    step = 1 if slc.step is None else slc.step
    assert step != 0, "slice step cannot be zero"
    default_start = 0 if step > 0 else length - 1
    default_end = length if step > 0 else 0
    return range(
        default_start if slc.start is None else (length + slc.start) if slc.start < 0 else slc.start,
        default_end if slc.stop is None else max(-1, (length + slc.stop)) if slc.stop < 0 else min(slc.stop, length),
        step
    )

def range_from_slice(
    slc: slice,  # slice used to generate the range
    length: int,  # the length of the iterable the slice is applied to
) -> range:  # range equivalent of the slice for an iterator of a given length
    '''Given a python slice object and a given length, return a range representing the indices that should be returned for that slice for a collection of that length (useful for implementing __getitem__ for slice as index)'''
    return range(length)[slc]