def clean_comment(line):
    """
    Clean up a comment, removing # , #! and starting space,
    and adding missing \n if necessary
    >>> clean_comment("#")
    '\n'
    >>> clean_comment("# This is ...")
    'This is ...\n'
    >>> clean_comment("#! This is ...")
    'This is ...\n'
    """
    if line.startswith("#!"):
        line = line[2:]
    else:
        line = line[1:]
    if line.startswith(" "):
        line = line[1:]
    if not line.endswith('\n'):
        line += '\n'
    return line