debugging fileinput

[Kyoskyu]

I'm using fileinput to go through the lines in a file using something
like:

import fileinput, string
for line in fileinput.input():
	process(strip(line))

However, for some reason, this snippet of code gets to the end of the file
and starts again at the beginning.  I'm at a loss as to how to debug this
problem.  If someone has any ideas or knows the reason, I'd appreciate the
help.  Thanks.