Programming help in python 2.6

'''
    $ # invoke doctest on /tmp/p.py using bash.
    $ ( cd /tmp && python -m doctest p.py )
'''
import re
import sys
import argparse # if you can understand this, it's good to use.

def accept(fyeah,fnay,strings):
    return [s for s in strings if fyeah(s) and not fnay(s)]

def main(keep_pattern,discard_pattern,strings):
    '''
        >>> main(*('a','b','a b ab xa xab xb yzs'.split()))
        ['a', 'xa']
    '''
    y = re.compile(keep_pattern)
    n = re.compile(discard_pattern)
    return accept(y.search,n.search,strings)

if '__main__' == __name__:
    argv = sys.argv
    try:
        retain,discard = argv[1:3]
        file_names = argv[3:]
    except:
        sys.stderr.write('\nUse: %s retain_pattern discard_pattern [files...]\n'%argv[0])
        sys.exit(1)
    retained_names = main(retain,discard,file_names)
    print(str(retained_names))

inf = open('filename','r')
i = 0
for LINE in inf.readlines():
    i += 1  # line number
    LINE # line at line number