#---------- randline.py----------#
#!/usr/bin/python
"""Iterate over random lines in a file (req Python 2.2+)
From command-line use: % randline.py <fname> <numlines>
"""
import sys
from os import stat, linesep
from stat import ST_SIZE
from random import randrange
MAX_LINE_LEN = 4096

#-- Iterable class
class randline(object):
    __slots__ = ('_fp','_size','_limit')
    def __init__(self, fname, limit=sys.maxint):
        self._size = stat(fname)[ST_SIZE]
        self._fp = open(fname,'rb')
        self._limit = limit
    def __iter__(self):
        return self
    def next(self):
        if self._limit <= 0:
            raise StopIteration
        self._limit -= 1
        pos = randrange(self._size)
        priorlen = min(pos, MAX_LINE_LEN)   # maybe near start
        self._fp.seek(pos-priorlen)
        # Add extra linesep at beg/end in case pos at beg/end
        prior = linesep + self._fp.read(priorlen)
        post = self._fp.read(MAX_LINE_LEN) + linesep
        begln = prior.rfind(linesep) + len(linesep)
        endln = post.find(linesep)
        return prior[begln:]+post[:endln]

#-- Use as command-line tool
if __name__=='__main__':
    fname, numlines = sys.argv[1], int(sys.argv[2])
    for line in randline(fname, numlines):
        print line