range_extensions.py

def inclusive_range(start: int, stop: int) -> range:
    """
    >>> list(inclusive_range(0, -1))
    [0, -1]
    """
    if stop > start:
        return range(start, stop + 1)
    return range(start, stop - 1, -1)


def intersection(a: range, b: range) -> range:
    """
    Return the intersection of two one-step ranges as a new range. The new
    range will have the step sign of `a` if `a` and `b` differ.

    Usage:
    >>> tuple(intersection(inclusive_range(0, 2), inclusive_range(1, 3)))
    (1, 2)
    >>> tuple(intersection(inclusive_range(2, 0), inclusive_range(3, 1)))
    (2, 1)
    >>> tuple(intersection(inclusive_range(0, 2), inclusive_range(3, 1)))
    (1, 2)
    >>> tuple(intersection(inclusive_range(3, 1), inclusive_range(0, 2)))
    (2, 1)
    """
    assert not {a.step, b.step} - {1, -1}

    if 1 == b.step == a.step:
        return range(max(a.start, b.start), min(a.stop, b.stop), a.step)
    elif -1 == b.step == a.step:
        return range(min(a.start, b.start), max(a.stop, b.stop), a.step)
    elif 1 == a.step:
        # a is increasing, b is decreasing
        return range(max(a.start, b.stop) + 1, min(a.stop, b.start), a.step)
    elif -1 == a.step:
        # a is decreasing, b is increasing
        return range(min(a.start, b.stop) - 1, max(a.stop, b.start), a.step)

    raise TypeError