def get_distance(annotation_1, annotation_2):
    """
    Compute distance between two CDS locations on
    the same genome
    
    Parameters
    ----------
    annotation_1 : tuple of (int, int)
        genome start and end location for the first CDS
    annotation_2 : tuple of (int, int)
        genome start and end location for the first CDS
        
    Returns
    -------
    int
        Distance between gene 1 and gene 2 on the
        ENA genome
    """

    # extract the two locations from the annotation
    # sort each so that smaller genome position is first
    location_1 = sorted(annotation_1)
    location_2 = sorted(annotation_2)

    # sort the two annotations so that the one with
    # an earlier start site is first
    x, y = sorted((location_1, location_2))

    # if not overlapping, calculate the distance
    if x[0] <= x[1] < y[0]:
        return y[0] - x[1]

    # if overlapping, return 0
    return 0