[python] How to iterate over the file in python

Just use for x in f: ..., this gives you line after line, is much shorter and readable (partly because it automatically stops when the file ends) and also saves you the rstrip call because the trailing newline is already stipped.

The error is caused by the exit condition, which can never be true: Even if the file is exhausted, readline will return an empty string, not None. Also note that you could still run into trouble with empty lines, e.g. at the end of the file. Adding if line.strip() == "": continue makes the code ignore blank lines, which is propably a good thing anyway.