def _is_A_list_company_symbol(code: str) -> bool:
    """测试code是否是符合A股代码要求的字符串
    Precondition
    =======================================================================================
    :param code: A股代码

    Post condition
    =======================================================================================
    :return: True or False

    Examples:
    =======================================================================================
    >>> _is_A_list_company_symbol('300072')
    True

    >>> _is_A_list_company_symbol(300072)
    Traceback (most recent call last):
    ...
    AssertionError

    >>> _is_A_list_company_symbol('300072.SZ')
    False

    >>> _is_A_list_company_symbol('700072.SZ')
    False
    """
    assert isinstance(code, str)
    return code.isdigit() \
           and len(code) == 6 \
           and code[:3] in ('000', '002', '300', '600', '601', '603', '608', '688')