cut.py

import argparse

COMMA = ','
DASH = '-'


def split_fields(fields, delimiter):
    if delimiter in fields:
        start, end = fields.split(delimiter)
        start = int(start or 0)
        end = int(end or 0)
        if not (start or end):
            raise ValueError("fields are numbered from 1")
    else:
        raise SyntaxError("Hey, only commas and hyphens are allowed")
    return start, end


def cut_text(args):
    delim = args.d or None
    file = args.file[0]
    fields = args.f

    file_lines = [line.strip().split(delim) for line in open(file).readlines()]

    if delim and len(delim) > 1:
        raise ValueError("the delimiter must be a single character")

    if COMMA in fields:
        start, end = split_fields(fields, COMMA)
        print (file_lines)
        for field in file_lines:
            try:
                print(field[start-1], field[end-1])
            except IndexError:
                print()
    elif DASH in fields:
        start, end = split_fields(fields, DASH)
        for field in file_lines:
            try:
                if not end:
                    print(delim.join(field[start-1:]))
                elif not start:
                    print(delim.join(field[:end+1]))
                else:
                    print(delim.join(field[start-1:end+1]))
            except IndexError:
                print()


def process_args():
    parser = argparse.ArgumentParser()

    parser.add_argument("-d")
    parser.add_argument("-f", required=True)
    parser.add_argument("file", nargs=1, type=str)

    args = parser.parse_args()

    return args

cut_text(process_args())