#! /usr/bin/env python3
"""
Truncate a file to a given length.
"""
import argparse


def truncate(filename, length):
    """
    Truncate the file
    :param filename:
    :param length:
    :return:
    """
    with open(filename) as f:
        lines = [line for line in f]

    with open(filename, 'w') as f:
        f.writelines(lines[-length:])


def main():
    """
    The main function
    :return:
    """
    parser = argparse.ArgumentParser()

    parser.add_argument(
        'file',
        type=str,
        help='Input file name'
    )

    parser.add_argument(
        'length',
        type=int,
        help='Number of lines to truncate to'
    )

    args = parser.parse_args()
    return truncate(args.file, args.length)


if __name__ == '__main__':
    main()