Read a random line from a file, supporting stdin

randline.py

#!/usr/bin/env python

import random
import sys

def random_line(file_handle):
    lines = file_handle.readlines()
    num_lines = len(lines)

    random_line = None
    while not random_line:
        random_line_num = random.randint(0, num_lines - 1)
        random_line = lines[random_line_num]
        random_line = random_line.strip()

    return random_line

file_handle = None

if len(sys.argv) < 2:
    sys.stderr.write("Reading stdin\n")
    file_handle = sys.stdin
else:
    file_handle = open(sys.argv[1])

print(random_line(file_handle))

file_handle.close()