def is_directives_header(s: str) -> bool:
    """
    Checks whether passed string is a cython header line.
    Ex: '# cython: infer_types=True'
    :param s: str
    :return: bool
    """
    s = s.lstrip()
    if not s[0] == '#':
        return False

    s = s[1:].lstrip()
    return s.startswith('cython:')