"Maximum recursion depth exceeded"...why?

[Thomas Allen]

I must not be understanding something. This is a simple recursive
function that prints all HTML files in argv[1] as its scans the
directory's contents. Why do I get a RuntimeError for recursion depth
exceeded?

#!/usr/bin/env python

import os, sys

def main():
    absToRel(sys.argv[1], sys.argv[2])

def absToRel(dir, root):
    for filename in os.listdir(dir):
        if os.path.isdir(filename):
            absToRel(filename, root)
        else:
            if(filename.endswith("html") or filename.endswith("htm")):
                print filename

if __name__ == "__main__":
    main()