def get_range(context, range_str):
    """Should be given a range_str like '<start_index>:<end_index', e.g. '1:4'

    returns a string: e.g. 1,2,3
    """
    rargs = [int(s) for s in range_str.split(':')]
    return ','.join([str(d) for d in range(*rargs)])