#!/usr/bin/env python
"""
randline.py - Read a Random Line from a File
Author: Sean B. Palmer, inamidst.com
"""

import sys, random, fileinput
from optparse import OptionParser

def randline(lines, ignore=False): 
   # Cf. http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/59865
   # via http://swhack.com/logs/2006-01-12#T22-05-54
   g = enumerate(lines)

   try: i, result = g.next()
   except StopIteration: return
   else: 
      if ignore and not result.strip(): 
         result = None

   for i, line in g: 
      if ignore and not line.strip(): 
         continue
      if random.uniform(0, i) < 1: 
         result = line
   return result

def main(argv=None): 
   parser = OptionParser(usage='%prog [options] <filename>*')
   parser.add_option('-i', '--ignore', action='store_true', default=False, 
                     help='ignore blank lines')
   options, args = parser.parse_args(argv)

   lines = fileinput.input(args or ['-'])
   result = randline(lines, ignore=options.ignore)
   sys.stdout.write(result)

if __name__=="__main__": 
   main()