python - datetime.strptime() AM PM 规范

Question

>>> datetime.strptime('2017-07-04 12:24:11', "%Y-%m-%d %I:%M:%S")
datetime.datetime(2017, 7, 4, 0, 24, 11)

为什么上面的转换得到一个小时的 0 ？如果我指的是 12 小时格式的下午 12:24:11 呢？

12 小时格式:

2017-07-04 午夜后不久的 12:24:11 将被指定为 12:24:11

和

2017-07-04 中午过后的 12:24:11 也将​​指定为 12:24:11

为什么它会在午夜后不久假设并将其转换为时间？

我希望它会给出警告或错误，因为我的时间字符串不够具体。

Answer 1

该行为一定是设计决定。这是 _strptime function in \Lib\_strptime.py 的相关部分

    elif group_key == 'I':
        hour = int(found_dict['I'])
        ampm = found_dict.get('p', '').lower()
        # If there was no AM/PM indicator, we'll treat this like AM
        if ampm in ('', locale_time.am_pm[0]):
            # We're in AM so the hour is correct unless we're
            # looking at 12 midnight.
            # 12 midnight == 12 AM == hour 0
            if hour == 12:
                hour = 0
        elif ampm == locale_time.am_pm[1]:
            # We're in PM so we need to add 12 to the hour unless
            # we're looking at 12 noon.
            # 12 noon == 12 PM == hour 12
            if hour != 12:

你可以自定义它来做你想做的事..

class foo(datetime.datetime):
    """foo(year, month, day[, hour[, minute[, second[, microsecond[,tzinfo]]]]])

    The year, month and day arguments are required. tzinfo may be None, or an
    instance of a tzinfo subclass. The remaining arguments may be ints.
    """

    @classmethod
    def strptime(cls, datestring, fmt):
        if '%I' in fmt and not any(attr in datestring for attr
                                   in ('AM', 'am', 'PM', 'pm')):
            print('Ambiguous datestring with twelve hour format')
            #raise ValueError('Ambiguous datestring with twelve hour format')
        return super().strptime(datestring, fmt)

---

我想您可以大胆尝试并通过您的修改重现 _strptime 函数，然后适本地分配它以产生更无缝的东西，但我不知道这有多明智。这就是人们所说的猴子补丁吗？