Returns generator that contains filenames
       from root directory and ends with suffix

def files_with_exts(root='.', suffix=''):
    """Returns generator that contains filenames
       from root directory and ends with suffix
    """
    return (os.path.join(rootdir, filename)
            for rootdir, dirnames, filenames in os.walk(root)
            for filename in filenames
            if filename.endswith(suffix))