def blank_line(ascii_file):
    """Returns True if the next line contains only white space; False otherwise (including comments)."""

    file_pos = ascii_file.tell()
    line = ascii_file.readline()
    ascii_file.seek(file_pos)
    if len(line) == 0:
        return True  # end of file
    words = line.split()
    return len(words) == 0