Python: linecache

SOLVED below

hi,

I wrote a small code. I get a strange error that i can't understand.
Here the exemp, if i use:

....
    line = linecache.getline(opts.filename, opts.n)
    print line
    print opts.filename
    print opts.n

I get first an empty line (the file is not empty at all), the file name and the integer correct:

then if without any change except replace

line = linecache.getline(opts.filename, opts.n) 
with
line = linecache.getline('fileinput', 10)

I get the result correct:

Is very strange for me, maybe there's something that i miss in using linecache.
Any idea?
Thanks a lot

D
_________________________________________EDIT

sorry for the useless post i got it,
i have to cast opts.n with int(opts.n)