How to use the pyfaidx.ucsc_split function in pyfaidx

def split_regions(args):
    if args.bed:
        regions_to_fetch = args.bed
        split_function = bed_split
    else:
        regions_to_fetch = args.regions
        split_function = ucsc_split
    return (regions_to_fetch, split_function)

def write_sequence(args):
    _, ext = os.path.splitext(args.fasta)
    if ext:
        ext = ext[1:]  # remove the dot from extension
    filt_function = re.compile(args.regex).search
    fasta = Fasta(args.fasta, default_seq=args.default_seq, key_function=eval(args.header_function), strict_bounds=not args.lazy, split_char=args.delimiter, filt_function=filt_function, read_long_names=args.long_names, rebuild=not args.no_rebuild)

    regions_to_fetch, split_function = split_regions(args)
    if not regions_to_fetch:
        regions_to_fetch = fasta.keys()
    if args.invert_match:
        sequences_to_exclude = set([split_function(region)[0] for region in regions_to_fetch])
        fasta = Fasta(args.fasta, default_seq=args.default_seq, key_function=eval(args.header_function), strict_bounds=not args.lazy, split_char=args.delimiter, rebuild=not args.no_rebuild)
        regions_to_fetch = (key for key in fasta.keys() if key not in sequences_to_exclude)
        split_function = ucsc_split

    header = False
    for region in regions_to_fetch:
        name, start, end = split_function(region)
        if args.size_range:
            if start is not None and end is not None:
                sequence_len = end - start
            else:
                sequence_len = len(fasta[name])
            if args.size_range[0] > sequence_len or args.size_range[1] < sequence_len:
                continue
        if args.split_files:  # open output file based on sequence name
            filename = '.'.join(str(e) for e in (name, start, end, ext) if e)
            filename = ''.join(c for c in filename if c.isalnum() or c in keepcharacters)
            outfile = open(filename, 'w')
        elif args.out: