Read random lines from a file

read_random_line_from_file.py

#!/usr/bin/python3

import sys
import getopt
import codecs
import secrets
import hashlib
from typing import List

def usage():
    print('Usage: {} -i [INPUT] -o [OUTPUT] -e [ENCODING] -n [NUMBER]'
            .format(sys.argv[0]))

def read_lines_from_file(filename: str,
                         lines: List[int],
                         encoding: str ='utf-8') -> List[str]:
    lines = sorted(lines)
    contents = []

    with codecs.open(filename, mode='r', encoding=encoding) as f:
        for i, line in enumerate(f):
            if len(lines) == 0:
                return contents;
            if lines[0] == i:
                contents.append(line.strip())
                lines.pop(0)

def gen_rand_nums(n: int, upper: int):
    line_nos = []
    for i in range(n):
        line_nos.append(secrets.randbelow(upper))
    return line_nos

def get_no_of_lines_in_file(filename: str, encoding: str):
    with open(filename, mode='r', encoding=encoding) as f:
        for i, _ in enumerate(f):
            pass
    return i + 1

def get_hash(s: str, algo: str):
    h = hashlib.new(algo)
    h.update(s.encode())
    return h.hexdigest()

def main(argv):
    input_file = ''
    output_file = ''
    encoding = ''
    num_of_lines = 0

    try:
        opts, args = getopt.getopt(argv, 'hi:o:e:n:')
    except getopt.GetoptError:
        usage()
        sys.exit(2)

    for opt, arg in opts:
        if opt in ('-h', '--help'):
            usage()
            sys.exit(0)
        elif opt == '-i':
            input_file = arg
        elif opt == '-o':
            output_file = arg
        elif opt == '-e':
            encoding = arg
        elif opt == '-n':
            num_of_lines = int(arg)

    if (input_file == '' or
            output_file == '' or
            encoding == '' or
            num_of_lines == 0):
        usage()
        sys.exit(3)

    line_nos = gen_rand_nums(num_of_lines,
                             get_no_of_lines_in_file(input_file, encoding))

    contents = read_lines_from_file(input_file, line_nos, encoding=encoding)

    with open(output_file, mode='w') as f:
        for content in contents:
            f.write(content + '\n')

if __name__ == '__main__':
    main(sys.argv[1:])
else:
    print('This script must be executed directly.')
    usage()
    sys.exit(1)