# `datetime` --- 基础 日期 和 时间 数据类型

源代码： Lib/datetime.py

`datetime` 模块提供了可以通过多种方式操作日期和时间的类。在支持日期时间数学运算的同时，实现的关注点更着重于如何能够更有效地解析其属性用于格式化输出和数据操作。相关功能可以参阅 `time` 和 `calendar` 模块。

有两种日期和时间的对象：天真型和觉悟型。

觉悟型对象有着用足以支持一些应用层面算法和国家层面时间调整的信息，例如时区和夏令时，来让自己和其他的觉悟型对象区别开来。觉悟型对象是用来表达不对解释器开放的特定时间信息 1。

天真型对象没包含足够多的信息来明确定位与之相关的 "date"对象和"time"对象。天真型对象代表的是 世界标准时间(UTC), 当地时间或者是其它时区的时间完全取决于程序就像一个数字是代表的是米、英里或者质量完全取决于程序。天真型对象以忽略了一些现实情况的为代价使得它容易理解和使用。

对于需要觉悟型对象的应用， `datetime` 对象和 `time` 对象有一个可选的时区信息属性 `tzinfo` ，这个属性可以设置给 `tzinfo` 类的子类实例。这些 `tzinfo` 对象捕获关于相对于世界标准时间（UTC）偏移、时区名字和夏令时是否有效等信息。需要注意的是，只有一个具体的 `tzinfo` 类，即由 `datetime` 模块提供的 `timezone` 类。 `timezone` 类可以代表相对于世界标准时间（UTC）固定偏移的简单时区，比如世界标准时间（UTC）自己或者北美东部时间或者东部夏令时。支持时区的详细程度取决于应用。世界各地的时间调整规则相比理性更加政治性，经常会变更。也没有一个基于世界标准时间（UTC）的标准套件适合用于所有应用。

The `datetime` module exports the following constants:

`datetime.``MINYEAR`

  `date` 或者 `datetime` 对象允许的最小年份。 常量 `MINYEAR` 是 `1` 。

`datetime.``MAXYEAR`

  `date` 或 `datetime` 对象允许最大的年份。常量 `MAXYEAR` 是 `9999` 。

参见

模块 `calendar`

  日历相关函数

模块 `time`

  时间的访问和转换

## 有效的类型

class `datetime.``date`

  理想的天真型日期假设公历是永远有效的。属性 : `year`, `month`, and `day` 。

class `datetime.``time`

  一个理想的时间独立于任何一天，假设每一天一共有24*60*60秒（这里没有"闰秒"的概念）。属性： `hour`, `minute`, `second`, `microsecond`, 和 `tzinfo`。

class `datetime.``datetime`

  日期和时间的结合。属性：`year`, `month`, `day`, `hour`, `minute`, `second`, `microsecond`, and `tzinfo`.

class `datetime.``timedelta`

  表示两个 `date` 对象或者 `time` 对象,或者 `datetime` 对象之间的时间间隔，精确到微秒。

class `datetime.``tzinfo`

  一个描述时区信息的抽象基类。用于给 `datetime` 类和 `time` 类提供自定义的时间调整概念（例如，负责时区或者夏令时）。

class `datetime.``timezone`

  一个实现了 `tzinfo` 抽象基类的子类，用于表示相对于 世界标准时间（UTC）的偏移量。

  3.2 新版功能.

这些类型的对象都是不可变的。

`date` 类型 的对象都是 天真型 的。

An object of type `time` or `datetime` may be naive or aware. A `datetime` object d is aware if `d.tzinfo` is not `None` and `d.tzinfo.utcoffset(d)` does not return `None`. If `d.tzinfo` is `None`, or if `d.tzinfo` is not `None` but `d.tzinfo.utcoffset(d)` returns `None`, d is naive. A `time` object t is aware if `t.tzinfo` is not `None` and `t.tzinfo.utcoffset(None)` does not return `None`. Otherwise, t is naive.

天真型和觉悟型之间的差别不适用于 `timedelta` 对象。

子类关系

    object
        timedelta
        tzinfo
            timezone
        time
        date
            datetime

## `timedelta` 类对象

`timedelta` 对象表示两个 date 或者 time 的时间间隔。

class `datetime.``timedelta`(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)

  所有的参数都是可选的并且默认为 `0`。这些参数可以是整数或者浮点数，也可以是正数或者负数。

  只有 days,*seconds* 和 microseconds 会存储在内部，即python内部以 days,*seconds* 和 microseconds 三个单位作为存储的基本单位。参数单位转换规则如下：

  - 1毫秒会转换成1000微秒。

  - 1分钟会转换成60秒。

  - 1小时会转换成3600秒。

  - 1星期会转换成7天。

  days, seconds, microseconds 本身也是标准化的，以保证表达方式的唯一性，例：

  - `0 <= microseconds < 1000000`

  - `0 <= seconds < 3600*24` (一天的秒数)

  - `-999999999 <= days <= 999999999`

  在有任何浮点型参数或者微秒为小数的情况下，所有小数均会按照前面的换算规则叠加到下一级，并使用round-half-to-even的方法对微秒进行取舍。没有浮点型参数情况下，转换的过程就是精确的（没有信息丢失）。

  如果标准化后的 days 数值超过了指定范围，将会抛出 `OverflowError` 异常。

  需要注意的是，负数被标准化后的结果会让你大吃一惊。例如，

      >>> from datetime import timedelta
      >>> d = timedelta(microseconds=-1)
      >>> (d.days, d.seconds, d.microseconds)
      (-1, 86399, 999999)

类属性：

`timedelta.``min`

  The most negative `timedelta` object, `timedelta(-999999999)`.

`timedelta.``max`

  The most positive `timedelta` object, `timedelta(days=999999999, hours=23, minutes=59, seconds=59, microseconds=999999)`.

`timedelta.``resolution`

  两个不相等的 `timedelta` 类对象最小的间隔为 `timedelta(microseconds=1)`。

需要注意的是，因为标准化的缘故，`timedelta.max` > `-timedelta.min`，`-timedelta.max` 不可以表示一个 `timedelta` 类对象。

实例属性（只读）：

属性 | 值
--- | ---
`days` | -999999999 至 999999999 ，含999999999
`seconds` | 0 至 86399，包含86399
`microseconds` | 0 至 999999，包含999999

支持的运算：

运算 | 结果
--- | ---
`t1 = t2 + t3` | t2 和 t3 的总和。 t1-t2 == t3 和 t1-t3 == t2 的值永远为真。(1)
`t1 = t2 - t3` | t2 减 t3 的差。t1 == t2 - t3 和 t2 == t1 + t3 值为永远为的真. (1)(6)
`t1 = t2 * i or t1 = i * t2` | 乘以一个整数。假如 `i != 0` 则 t1 // i == t2 的值为真。
| In general, t1 * i == t1 * (i-1) + t1 is true. (1)
`t1 = t2 * f or t1 = f * t2` | 乘以一个浮点数，小数结果使用 round-half-to-even 方式进行取舍。
`f = t2 / t3` | Division (3) of overall duration t2 by interval unit t3.返回一个 `float` 对象。
`t1 = t2 / f or t1 = t2 / i` | 除以一个 浮点数或者整数。小数结果采用 round-half-to-even 方法进行取舍。
`t1 = t2 // i` or `t1 = t2 // t3` | 取整除，余数部分(如果有的话)将被丢弃。在第二种情况下，返回一个整数。(3)
`t1 = t2 % t3` | 余数为一个 `timedelta` 对象。(3)
`q, r = divmod(t1, t2)` | 通过 : `q = t1 // t2` (3) and `r = t1 % t2` 计算出商和余数。q是一个整数，r是一个 `timedelta` 对象。
`+t1` | 返回一个相同数值的 `timedelta` 对象。
`-t1` | 等价于 `timedelta`(-t1.days, -t1.seconds, -t1.microseconds), 和 t1* -1. (1)(4)
`abs(t)` | 当 `t.days >= 0``时等于 +\ *t*, 当 ``t.days < 0` 时 -t 。 (2)
`str(t)` | 返回一个形如 `[D day[s], ][H]H:MM:SS[.UUUUUU]` 的字符串，当 `t` 为负数的时候， D 也为负数。 (5)
`repr(t)` | 返回一个 `timedelta` 对象的字符串表示形式，作为附带正规属性值的构造器调用。

注释:

1. 精确但可能会溢出。

2. 精确且不会溢出。

3. 除以0将会抛出异常 `ZeroDivisionError` 。

4. -timedelta.max 不是一个 `timedelta` 类对象。

5. String representations of `timedelta` objects are normalized similarly to their internal representation. This leads to somewhat unusual results for negative timedeltas. For example:

       >>> timedelta(hours=-5)
       datetime.timedelta(days=-1, seconds=68400)
       >>> print(_)
       -1 day, 19:00:00

6. 表达式 `t2 - t3` 通常与 `t2 + (-t3)` 是等价的，除非 t3 等于 `timedelta.max`; 在这种情况下前者会返回结果，而后者则会溢出。

除了上面列举的操作以外 `timedelta` 对象还支持与 `date` 和 `datetime` 对象进行特定的相加和相减运算（见下文）。

在 3.2 版更改: Floor division and true division of a `timedelta` object by another `timedelta` object are now supported, as are remainder operations and the `divmod()` function. True division and multiplication of a `timedelta` object by a `float` object are now supported.

Comparisons of `timedelta` objects are supported with the `timedelta` object representing the smaller duration considered to be the smaller timedelta. In order to stop mixed-type comparisons from falling back to the default comparison by object address, when a `timedelta` object is compared to an object of a different type, `TypeError` is raised unless the comparison is `==` or `!=`. The latter cases return `False` or `True`, respectively.

`timedelta` 对象是 hashable 类型的(可以作为字典关键字), 支持高效获取, 在布尔上下文中， `timedelta` 对象大多数情况下都被视为真，仅在不等于 `timedelta(0)` 时。

实例方法：

`timedelta.``total_seconds`()

  返回时间间隔包含了多少秒。造价于 `td / timedelta(seconds=1)`。对于其它单位可以直接使用除法的形式 (例如 `td / timedelta(microseconds=1)`)。

  需要注意的是，时间间隔较大时，这个方法的结果中的微秒将会失真（大多数平台上大于270年视为一个较大的时间间隔）。

  3.2 新版功能.

用法示例：

    >>> from datetime import timedelta
    >>> year = timedelta(days=365)
    >>> another_year = timedelta(weeks=40, days=84, hours=23,
    ...                          minutes=50, seconds=600)  # adds up to 365 days
    >>> year.total_seconds()
    31536000.0
    >>> year == another_year
    True
    >>> ten_years = 10 * year
    >>> ten_years, ten_years.days // 365
    (datetime.timedelta(days=3650), 10)
    >>> nine_years = ten_years - year
    >>> nine_years, nine_years.days // 365
    (datetime.timedelta(days=3285), 9)
    >>> three_years = nine_years // 3
    >>> three_years, three_years.days // 365
    (datetime.timedelta(days=1095), 3)
    >>> abs(three_years - ten_years) == 2 * three_years + year
    True

## `date` 对象

A `date` object represents a date (year, month and day) in an idealized calendar, the current Gregorian calendar indefinitely extended in both directions. January 1 of year 1 is called day number 1, January 2 of year 1 is called day number 2, and so on. This matches the definition of the "proleptic Gregorian" calendar in Dershowitz and Reingold's book Calendrical Calculations, where it's the base calendar for all computations. See the book for algorithms for converting between proleptic Gregorian ordinals and many other calendar systems.

class `datetime.``date`(year, month, day)

  所有参数都是必选的。参数可以是在下面范围内的整数：

  - `MINYEAR <= year <= MAXYEAR`

  - `1 <= month <= 12`

  - `1 <= 日期 <= 给定年月对应的天数`

  如果参数不在这些范围内，则抛出 `ValueError` 异常。

其它构造器，所有的类方法：

classmethod `date.``today`()

  返回当地的当前日期。与``date.fromtimestamp(time.time())``等价。

classmethod `date.``fromtimestamp`(timestamp)

  Return the local date corresponding to the POSIX timestamp, such as is returned by `time.time()`. This may raise `OverflowError`, if the timestamp is out of the range of values supported by the platform C `localtime()` function, and `OSError` on `localtime()` failure. It's common for this to be restricted to years from 1970 through 2038. Note that on non-POSIX systems that include leap seconds in their notion of a timestamp, leap seconds are ignored by `fromtimestamp()`.

  在 3.3 版更改: Raise `OverflowError` instead of `ValueError` if the timestamp is out of the range of values supported by the platform C `localtime()` function. Raise `OSError` instead of `ValueError` on `localtime()` failure.

classmethod `date.``fromordinal`(ordinal)

  Return the date corresponding to the proleptic Gregorian ordinal, where January 1 of year 1 has ordinal 1. `ValueError` is raised unless `1 <= ordinal <= date.max.toordinal()`. For any date d, `date.fromordinal(d.toordinal()) == d`.

classmethod `date.``fromisoformat`(date_string)

  Return a `date` corresponding to a date_string in the format emitted by `date.isoformat()`. Specifically, this function supports strings in the format(s) `YYYY-MM-DD`.

  警告

  This does not support parsing arbitrary ISO 8601 strings - it is only intended as the inverse operation of `date.isoformat()`.

  3.7 新版功能.

classmethod `date.``fromisocalendar`(year, week, day)

  Return a `date` corresponding to the ISO calendar date specified by year, week and day. This is the inverse of the function `date.isocalendar()`.

  3.8 新版功能.

类属性：

`date.``min`

  最小的日期 `date(MINYEAR, 1, 1)` 。

`date.``max`

  最大的日期 ，`date(MAXYEAR, 12, 31)`。

`date.``resolution`

  两个日期对象的最小间隔，`timedelta(days=1)`。

实例属性（只读）：

`date.``year`

  在 `MINYEAR` 和 `MAXYEAR` 之间，包含边界。

`date.``month`

  1 至 12（含）

`date.``day`

  返回1到指定年月的天数间的数字。

支持的运算：

运算 | 结果
--- | ---
`date2 = date1 + timedelta` | date2 is `timedelta.days` days removed from date1. (1)
`date2 = date1 - timedelta` | Computes date2 such that `date2 + timedelta == date1`. (2)
`timedelta = date1 - date2` | (3)
`date1 < date2` | date1 is considered less than date2 when date1 precedes date2 in time. (4)

注释:

1. date2 is moved forward in time if `timedelta.days > 0`, or backward if `timedelta.days < 0`. Afterward `date2 - date1 == timedelta.days`. `timedelta.seconds` and `timedelta.microseconds` are ignored. `OverflowError` is raised if `date2.year` would be smaller than `MINYEAR` or larger than `MAXYEAR`.

2. `timedelta.seconds` 和 `timedelta.microseconds` 是被忽略的。

3. 精确且不会溢出。timedelta.seconds 和 timedelta.microseconds 均为0， 同时 date2 + timedelta == date1 是成立的。

4. In other words, `date1 < date2` if and only if `date1.toordinal() < date2.toordinal()`. Date comparison raises `TypeError` if the other comparand isn't also a `date` object. However, `NotImplemented` is returned instead if the other comparand has a `timetuple()` attribute. This hook gives other kinds of date objects a chance at implementing mixed-type comparison. If not, when a `date` object is compared to an object of a different type, `TypeError` is raised unless the comparison is `==` or `!=`. The latter cases return `False` or `True`, respectively.

日期可以作为字典的关键字。在布尔上下文中，所有的 `date` 对象都视为真。

实例方法：

`date.``replace`(year=self.year, month=self.month, day=self.day)

  Return a date with the same value, except for those parameters given new values by whichever keyword arguments are specified. For example, if `d == date(2002, 12, 31)`, then `d.replace(day=26) == date(2002, 12, 26)`.

`date.``timetuple`()

  Return a `time.struct_time` such as returned by `time.localtime()`. The hours, minutes and seconds are 0, and the DST flag is -1. `d.timetuple()` is equivalent to `time.struct_time((d.year, d.month, d.day, 0, 0, 0, d.weekday(), yday, -1))`, where `yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1` is the day number within the current year starting with `1` for January 1st.

`date.``toordinal`()

  Return the proleptic Gregorian ordinal of the date, where January 1 of year 1 has ordinal 1. For any `date` object d, `date.fromordinal(d.toordinal()) == d`.

`date.``weekday`()

  返回一个整数代表星期几，星期一为0，星期天为6。例如， `date(2002, 12, 4).weekday() == 2`，表示的是星期三。参阅 `isoweekday()`。

`date.``isoweekday`()

  返回一个整数代表星期几，星期一为1，星期天为7。例如：`date(2002, 12, 4).isoweekday() == 3`,表示星期三。参见 `weekday()`, `isocalendar()`。

`date.``isocalendar`()

  返回一个三元元组，(ISO year, ISO week number, ISO weekday) 。

  ISO日历是一个被广泛使用的公历。可以从 https://www.staff.science.uu.nl/~gent0113/calendar/isocalendar.htm 上查看更完整的说明。

  The ISO year consists of 52 or 53 full weeks, and where a week starts on a Monday and ends on a Sunday. The first week of an ISO year is the first (Gregorian) calendar week of a year containing a Thursday. This is called week number 1, and the ISO year of that Thursday is the same as its Gregorian year.

  For example, 2004 begins on a Thursday, so the first week of ISO year 2004 begins on Monday, 29 Dec 2003 and ends on Sunday, 4 Jan 2004, so that `date(2003, 12, 29).isocalendar() == (2004, 1, 1)` and `date(2004, 1, 4).isocalendar() == (2004, 1, 7)`.

`date.``isoformat`()

  返回一个 ISO 8601 格式的字符串， 'YYYY-MM-DD'。例如 `date(2002, 12, 4).isoformat() == '2002-12-04'`。

`date.``__str__`()

  对于日期对象 d, `str(d)` 等价于 `d.isoformat()` 。

`date.``ctime`()

  Return a string representing the date, for example `date(2002, 12, 4).ctime() == 'Wed Dec 4 00:00:00 2002'`. `d.ctime()` is equivalent to `time.ctime(time.mktime(d.timetuple()))` on platforms where the native C `ctime()` function (which `time.ctime()` invokes, but which `date.ctime()` does not invoke) conforms to the C standard.

`date.``strftime`(format)

  Return a string representing the date, controlled by an explicit format string. Format codes referring to hours, minutes or seconds will see 0 values. For a complete list of formatting directives, see strftime() and strptime() Behavior.

`date.``__format__`(format)

  Same as `date.strftime()`. This makes it possible to specify a format string for a `date` object in formatted string literals and when using `str.format()`. For a complete list of formatting directives, see strftime() and strptime() Behavior.

Example of counting days to an event:

    >>> import time
    >>> from datetime import date
    >>> today = date.today()
    >>> today
    datetime.date(2007, 12, 5)
    >>> today == date.fromtimestamp(time.time())
    True
    >>> my_birthday = date(today.year, 6, 24)
    >>> if my_birthday < today:
    ...     my_birthday = my_birthday.replace(year=today.year + 1)
    >>> my_birthday
    datetime.date(2008, 6, 24)
    >>> time_to_birthday = abs(my_birthday - today)
    >>> time_to_birthday.days
    202

Example of working with `date`:

    >>> from datetime import date
    >>> d = date.fromordinal(730920) # 730920th day after 1. 1. 0001
    >>> d
    datetime.date(2002, 3, 11)
    >>> t = d.timetuple()
    >>> for i in t:
    ...     print(i)
    2002                # year
    3                   # month
    11                  # day
    0
    0
    0
    0                   # weekday (0 = Monday)
    70                  # 70th day in the year
    -1
    >>> ic = d.isocalendar()
    >>> for i in ic:
    ...     print(i)
    2002                # ISO year
    11                  # ISO week number
    1                   # ISO day number ( 1 = Monday )
    >>> d.isoformat()
    '2002-03-11'
    >>> d.strftime("%d/%m/%y")
    '11/03/02'
    >>> d.strftime("%A %d. %B %Y")
    'Monday 11. March 2002'
    >>> 'The {1} is {0:%d}, the {2} is {0:%B}.'.format(d, "day", "month")
    'The day is 11, the month is March.'

## `datetime` 对象

A `datetime` object is a single object containing all the information from a `date` object and a `time` object. Like a `date` object, `datetime` assumes the current Gregorian calendar extended in both directions; like a time object, `datetime` assumes there are exactly 3600*24 seconds in every day.

构造器 ：

class `datetime.``datetime`(year, month, day, hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)

  year, month, day 三个参数是必选的。 tzinfo 可以是 `None`, 或者是是一个 `tzinfo` 子类的实例。其余的参数可以是在以下范围内的整数：

  - `MINYEAR <= year <= MAXYEAR`,

  - `1 <= month <= 12`,

  - `1 <= day <= 指定年月的天数`,

  - `0 <= hour < 24`,

  - `0 <= minute < 60`,

  - `0 <= second < 60`,

  - `0 <= microsecond < 1000000`,

  - `fold in [0, 1]`.

  如果参数不在这些范围内，则抛出 `ValueError` 异常。

  3.6 新版功能: 增加了 `fold` 参数。

其它构造器，所有的类方法：

classmethod `datetime.``today`()

  Return the current local datetime, with `tzinfo` `None`. This is equivalent to `datetime.fromtimestamp(time.time())`. See also `now()`, `fromtimestamp()`.

classmethod `datetime.``now`(tz=None)

  Return the current local date and time. If optional argument tz is `None` or not specified, this is like `today()`, but, if possible, supplies more precision than can be gotten from going through a `time.time()` timestamp (for example, this may be possible on platforms supplying the C `gettimeofday()` function).

  If tz is not `None`, it must be an instance of a `tzinfo` subclass, and the current date and time are converted to tz’s time zone. In this case the result is equivalent to `tz.fromutc(datetime.utcnow().replace(tzinfo=tz))`. See also `today()`, `utcnow()`.

classmethod `datetime.``utcnow`()

  Return the current UTC date and time, with `tzinfo` `None`. This is like `now()`, but returns the current UTC date and time, as a naive `datetime` object. An aware current UTC datetime can be obtained by calling `datetime.now(timezone.utc)`. See also `now()`.

classmethod `datetime.``fromtimestamp`(timestamp, tz=None)

  Return the local date and time corresponding to the POSIX timestamp, such as is returned by `time.time()`. If optional argument tz is `None` or not specified, the timestamp is converted to the platform's local date and time, and the returned `datetime` object is naive.

  If tz is not `None`, it must be an instance of a `tzinfo` subclass, and the timestamp is converted to tz’s time zone. In this case the result is equivalent to `tz.fromutc(datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz))`.

  `fromtimestamp()` may raise `OverflowError`, if the timestamp is out of the range of values supported by the platform C `localtime()` or `gmtime()` functions, and `OSError` on `localtime()` or `gmtime()` failure. It's common for this to be restricted to years in 1970 through 2038. Note that on non-POSIX systems that include leap seconds in their notion of a timestamp, leap seconds are ignored by `fromtimestamp()`, and then it's possible to have two timestamps differing by a second that yield identical `datetime` objects. See also `utcfromtimestamp()`.

  在 3.3 版更改: Raise `OverflowError` instead of `ValueError` if the timestamp is out of the range of values supported by the platform C `localtime()` or `gmtime()` functions. Raise `OSError` instead of `ValueError` on `localtime()` or `gmtime()` failure.

  在 3.6 版更改: `fromtimestamp()` may return instances with `fold` set to 1.

classmethod `datetime.``utcfromtimestamp`(timestamp)

  Return the UTC `datetime` corresponding to the POSIX timestamp, with `tzinfo` `None`. This may raise `OverflowError`, if the timestamp is out of the range of values supported by the platform C `gmtime()` function, and `OSError` on `gmtime()` failure. It's common for this to be restricted to years in 1970 through 2038.

  To get an aware `datetime` object, call `fromtimestamp()`:

      datetime.fromtimestamp(timestamp, timezone.utc)

  On the POSIX compliant platforms, it is equivalent to the following expression:

      datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=timestamp)

  except the latter formula always supports the full years range: between `MINYEAR` and `MAXYEAR` inclusive.

  在 3.3 版更改: Raise `OverflowError` instead of `ValueError` if the timestamp is out of the range of values supported by the platform C `gmtime()` function. Raise `OSError` instead of `ValueError` on `gmtime()` failure.

classmethod `datetime.``fromordinal`(ordinal)

  Return the `datetime` corresponding to the proleptic Gregorian ordinal, where January 1 of year 1 has ordinal 1. `ValueError` is raised unless `1 <= ordinal <= datetime.max.toordinal()`. The hour, minute, second and microsecond of the result are all 0, and `tzinfo` is `None`.

classmethod `datetime.``combine`(date, time, tzinfo=self.tzinfo)

  Return a new `datetime` object whose date components are equal to the given `date` object's, and whose time components are equal to the given `time` object's. If the tzinfo argument is provided, its value is used to set the `tzinfo` attribute of the result, otherwise the `tzinfo` attribute of the time argument is used.

  For any `datetime` object d, `d == datetime.combine(d.date(), d.time(), d.tzinfo)`. If date is a `datetime` object, its time components and `tzinfo` attributes are ignored.

  在 3.6 版更改: Added the tzinfo argument.

classmethod `datetime.``fromisoformat`(date_string)

  Return a `datetime` corresponding to a date_string in one of the formats emitted by `date.isoformat()` and `datetime.isoformat()`. Specifically, this function supports strings in the format(s) `YYYY-MM-DD[*HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]]`, where `*` can match any single character.

  警告

  This does not support parsing arbitrary ISO 8601 strings - it is only intended as the inverse operation of `datetime.isoformat()`.

  3.7 新版功能.

classmethod `datetime.``fromisocalendar`(year, week, day)

  Return a `datetime` corresponding to the ISO calendar date specified by year, week and day. The non-date components of the datetime are populated with their normal default values. This is the inverse of the function `datetime.isocalendar()`.

  3.8 新版功能.

classmethod `datetime.``strptime`(date_string, format)

  Return a `datetime` corresponding to date_string, parsed according to format. This is equivalent to `datetime(*(time.strptime(date_string, format)[0:6]))`. `ValueError` is raised if the date_string and format can't be parsed by `time.strptime()` or if it returns a value which isn't a time tuple. For a complete list of formatting directives, see strftime() and strptime() Behavior.

类属性：

`datetime.``min`

  The earliest representable `datetime`, `datetime(MINYEAR, 1, 1, tzinfo=None)`.

`datetime.``max`

  The latest representable `datetime`, `datetime(MAXYEAR, 12, 31, 23, 59, 59, 999999, tzinfo=None)`.

`datetime.``resolution`

  The smallest possible difference between non-equal `datetime` objects, `timedelta(microseconds=1)`.

实例属性（只读）：

`datetime.``year`

  在 `MINYEAR` 和 `MAXYEAR` 之间，包含边界。

`datetime.``month`

  1 至 12（含）

`datetime.``day`

  返回1到指定年月的天数间的数字。

`datetime.``hour`

  In `range(24)`.

`datetime.``minute`

  In `range(60)`.

`datetime.``second`

  In `range(60)`.

`datetime.``microsecond`

  In `range(1000000)`.

`datetime.``tzinfo`

  The object passed as the tzinfo argument to the `datetime` constructor, or `None` if none was passed.

`datetime.``fold`

  In `[0, 1]`. Used to disambiguate wall times during a repeated interval. (A repeated interval occurs when clocks are rolled back at the end of daylight saving time or when the UTC offset for the current zone is decreased for political reasons.) The value 0 (1) represents the earlier (later) of the two moments with the same wall time representation.

  3.6 新版功能.

支持的运算：

运算 | 结果
--- | ---
`datetime2 = datetime1 + timedelta` | (1)
`datetime2 = datetime1 - timedelta` | (2)
`timedelta = datetime1 - datetime2` | (3)
`datetime1 < datetime2` | Compares `datetime` to `datetime`. (4)

1. datetime2 is a duration of timedelta removed from datetime1, moving forward in time if `timedelta.days` > 0, or backward if `timedelta.days` < 0. The result has the same `tzinfo` attribute as the input datetime, and datetime2 - datetime1 == timedelta after. `OverflowError` is raised if datetime2.year would be smaller than `MINYEAR` or larger than `MAXYEAR`. Note that no time zone adjustments are done even if the input is an aware object.

2. Computes the datetime2 such that datetime2 + timedelta == datetime1. As for addition, the result has the same `tzinfo` attribute as the input datetime, and no time zone adjustments are done even if the input is aware.

3. Subtraction of a `datetime` from a `datetime` is defined only if both operands are naive, or if both are aware. If one is aware and the other is naive, `TypeError` is raised.

   If both are naive, or both are aware and have the same `tzinfo` attribute, the `tzinfo` attributes are ignored, and the result is a `timedelta` object t such that `datetime2 + t == datetime1`. No time zone adjustments are done in this case.

   If both are aware and have different `tzinfo` attributes, `a-b` acts as if a and b were first converted to naive UTC datetimes first. The result is `(a.replace(tzinfo=None) - a.utcoffset()) - (b.replace(tzinfo=None) - b.utcoffset())` except that the implementation never overflows.

4. datetime1 is considered less than datetime2 when datetime1 precedes datetime2 in time.

   If one comparand is naive and the other is aware, `TypeError` is raised if an order comparison is attempted. For equality comparisons, naive instances are never equal to aware instances.

   If both comparands are aware, and have the same `tzinfo` attribute, the common `tzinfo` attribute is ignored and the base datetimes are compared. If both comparands are aware and have different `tzinfo` attributes, the comparands are first adjusted by subtracting their UTC offsets (obtained from `self.utcoffset()`).

   在 3.3 版更改: Equality comparisons between naive and aware `datetime` instances don't raise `TypeError`.

   注解

   In order to stop comparison from falling back to the default scheme of comparing object addresses, datetime comparison normally raises `TypeError` if the other comparand isn't also a `datetime` object. However, `NotImplemented` is returned instead if the other comparand has a `timetuple()` attribute. This hook gives other kinds of date objects a chance at implementing mixed-type comparison. If not, when a `datetime` object is compared to an object of a different type, `TypeError` is raised unless the comparison is `==` or `!=`. The latter cases return `False` or `True`, respectively.

`datetime` objects can be used as dictionary keys. In Boolean contexts, all `datetime` objects are considered to be true.

实例方法：

`datetime.``date`()

  Return `date` object with same year, month and day.

`datetime.``time`()

  Return `time` object with same hour, minute, second, microsecond and fold. `tzinfo` is `None`. See also method `timetz()`.

  在 3.6 版更改: The fold value is copied to the returned `time` object.

`datetime.``timetz`()

  Return `time` object with same hour, minute, second, microsecond, fold, and tzinfo attributes. See also method `time()`.

  在 3.6 版更改: The fold value is copied to the returned `time` object.

`datetime.``replace`(year=self.year, month=self.month, day=self.day, hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, * fold=0)

  Return a datetime with the same attributes, except for those attributes given new values by whichever keyword arguments are specified. Note that `tzinfo=None` can be specified to create a naive datetime from an aware datetime with no conversion of date and time data.

  3.6 新版功能: 增加了 `fold` 参数。

`datetime.``astimezone`(tz=None)

  Return a `datetime` object with new `tzinfo` attribute tz, adjusting the date and time data so the result is the same UTC time as self, but in tz's local time.

  If provided, tz must be an instance of a `tzinfo` subclass, and its `utcoffset()` and `dst()` methods must not return `None`. If self is naive, it is presumed to represent time in the system timezone.

  If called without arguments (or with `tz=None`) the system local timezone is assumed for the target timezone. The `.tzinfo` attribute of the converted datetime instance will be set to an instance of `timezone` with the zone name and offset obtained from the OS.

  If `self.tzinfo` is tz, `self.astimezone(tz)` is equal to self: no adjustment of date or time data is performed. Else the result is local time in the timezone tz, representing the same UTC time as self: after `astz = dt.astimezone(tz)`, `astz - astz.utcoffset()` will have the same date and time data as `dt - dt.utcoffset()`.

  If you merely want to attach a time zone object tz to a datetime dt without adjustment of date and time data, use `dt.replace(tzinfo=tz)`. If you merely want to remove the time zone object from an aware datetime dt without conversion of date and time data, use `dt.replace(tzinfo=None)`.

  Note that the default `tzinfo.fromutc()` method can be overridden in a `tzinfo` subclass to affect the result returned by `astimezone()`. Ignoring error cases, `astimezone()` acts like:

      def astimezone(self, tz):
          if self.tzinfo is tz:
              return self
          # Convert self to UTC, and attach the new time zone object.
          utc = (self - self.utcoffset()).replace(tzinfo=tz)
          # Convert from UTC to tz's local time.
          return tz.fromutc(utc)

  在 3.3 版更改: tz now can be omitted.

  在 3.6 版更改: The `astimezone()` method can now be called on naive instances that are presumed to represent system local time.

`datetime.``utcoffset`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.utcoffset(self)`, and raises an exception if the latter doesn't return `None` or a `timedelta` object with magnitude less than one day.

  在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

`datetime.``dst`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.dst(self)`, and raises an exception if the latter doesn't return `None` or a `timedelta` object with magnitude less than one day.

  在 3.7 版更改: The DST offset is not restricted to a whole number of minutes.

`datetime.``tzname`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.tzname(self)`, raises an exception if the latter doesn't return `None` or a string object,

`datetime.``timetuple`()

  Return a `time.struct_time` such as returned by `time.localtime()`. `d.timetuple()` is equivalent to `time.struct_time((d.year, d.month, d.day, d.hour, d.minute, d.second, d.weekday(), yday, dst))`, where `yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1` is the day number within the current year starting with `1` for January 1st. The `tm_isdst` flag of the result is set according to the `dst()` method: `tzinfo` is `None` or `dst()` returns `None`, `tm_isdst` is set to `-1`; else if `dst()` returns a non-zero value, `tm_isdst` is set to `1`; else `tm_isdst` is set to `0`.

`datetime.``utctimetuple`()

  If `datetime` instance d is naive, this is the same as `d.timetuple()` except that `tm_isdst` is forced to 0 regardless of what `d.dst()` returns. DST is never in effect for a UTC time.

  If d is aware, d is normalized to UTC time, by subtracting `d.utcoffset()`, and a `time.struct_time` for the normalized time is returned. `tm_isdst` is forced to 0. Note that an `OverflowError` may be raised if d.year was `MINYEAR` or `MAXYEAR` and UTC adjustment spills over a year boundary.

`datetime.``toordinal`()

  Return the proleptic Gregorian ordinal of the date. The same as `self.date().toordinal()`.

`datetime.``timestamp`()

  Return POSIX timestamp corresponding to the `datetime` instance. The return value is a `float` similar to that returned by `time.time()`.

  Naive `datetime` instances are assumed to represent local time and this method relies on the platform C `mktime()` function to perform the conversion. Since `datetime` supports wider range of values than `mktime()` on many platforms, this method may raise `OverflowError` for times far in the past or far in the future.

  For aware `datetime` instances, the return value is computed as:

      (dt - datetime(1970, 1, 1, tzinfo=timezone.utc)).total_seconds()

  3.3 新版功能.

  在 3.6 版更改: The `timestamp()` method uses the `fold` attribute to disambiguate the times during a repeated interval.

  注解

  There is no method to obtain the POSIX timestamp directly from a naive `datetime` instance representing UTC time. If your application uses this convention and your system timezone is not set to UTC, you can obtain the POSIX timestamp by supplying `tzinfo=timezone.utc`:

      timestamp = dt.replace(tzinfo=timezone.utc).timestamp()

  or by calculating the timestamp directly:

      timestamp = (dt - datetime(1970, 1, 1)) / timedelta(seconds=1)

`datetime.``weekday`()

  Return the day of the week as an integer, where Monday is 0 and Sunday is 6. The same as `self.date().weekday()`. See also `isoweekday()`.

`datetime.``isoweekday`()

  Return the day of the week as an integer, where Monday is 1 and Sunday is 7. The same as `self.date().isoweekday()`. See also `weekday()`, `isocalendar()`.

`datetime.``isocalendar`()

  Return a 3-tuple, (ISO year, ISO week number, ISO weekday). The same as `self.date().isocalendar()`.

`datetime.``isoformat`(sep='T', timespec='auto')

  Return a string representing the date and time in ISO 8601 format, YYYY-MM-DDTHH:MM:SS.ffffff or, if `microsecond` is 0, YYYY-MM-DDTHH:MM:SS

  If `utcoffset()` does not return `None`, a string is appended, giving the UTC offset: YYYY-MM-DDTHH:MM:SS.ffffff+HH:MM[:SS[.ffffff]] or, if `microsecond` is 0 YYYY-MM-DDTHH:MM:SS+HH:MM[:SS[.ffffff]].

  The optional argument sep (default `'T'`) is a one-character separator, placed between the date and time portions of the result. For example,

      >>> from datetime import tzinfo, timedelta, datetime
      >>> class TZ(tzinfo):
      ...     def utcoffset(self, dt): return timedelta(minutes=-399)
      ...
      >>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
      '2002-12-25 00:00:00-06:39'

  The optional argument timespec specifies the number of additional components of the time to include (the default is `'auto'`). It can be one of the following:

  - `'auto'`: Same as `'seconds'` if `microsecond` is 0, same as `'microseconds'` otherwise.

  - `'hours'`: Include the `hour` in the two-digit HH format.

  - `'minutes'`: Include `hour` and `minute` in HH:MM format.

  - `'seconds'`: Include `hour`, `minute`, and `second` in HH:MM:SS format.

  - `'milliseconds'`: Include full time, but truncate fractional second part to milliseconds. HH:MM:SS.sss format.

  - `'microseconds'`: Include full time in HH:MM:SS.ffffff format.

  注解

  Excluded time components are truncated, not rounded.

  `ValueError` will be raised on an invalid timespec argument.

      >>> from datetime import datetime
      >>> datetime.now().isoformat(timespec='minutes')   # doctest: +SKIP
      '2002-12-25T00:00'
      >>> dt = datetime(2015, 1, 1, 12, 30, 59, 0)
      >>> dt.isoformat(timespec='microseconds')
      '2015-01-01T12:30:59.000000'

  3.6 新版功能: Added the timespec argument.

`datetime.``__str__`()

  For a `datetime` instance d, `str(d)` is equivalent to `d.isoformat(' ')`.

`datetime.``ctime`()

  Return a string representing the date and time, for example `datetime(2002, 12, 4, 20, 30, 40).ctime() == 'Wed Dec 4 20:30:40 2002'`. `d.ctime()` is equivalent to `time.ctime(time.mktime(d.timetuple()))` on platforms where the native C `ctime()` function (which `time.ctime()` invokes, but which `datetime.ctime()` does not invoke) conforms to the C standard.

`datetime.``strftime`(format)

  Return a string representing the date and time, controlled by an explicit format string. For a complete list of formatting directives, see strftime() and strptime() Behavior.

`datetime.``__format__`(format)

  Same as `datetime.strftime()`. This makes it possible to specify a format string for a `datetime` object in formatted string literals and when using `str.format()`. For a complete list of formatting directives, see strftime() and strptime() Behavior.

Examples of working with datetime objects:

    >>> from datetime import datetime, date, time
    >>> # Using datetime.combine()
    >>> d = date(2005, 7, 14)
    >>> t = time(12, 30)
    >>> datetime.combine(d, t)
    datetime.datetime(2005, 7, 14, 12, 30)
    >>> # Using datetime.now() or datetime.utcnow()
    >>> datetime.now()
    datetime.datetime(2007, 12, 6, 16, 29, 43, 79043)   # GMT +1
    >>> datetime.utcnow()
    datetime.datetime(2007, 12, 6, 15, 29, 43, 79060)
    >>> # Using datetime.strptime()
    >>> dt = datetime.strptime("21/11/06 16:30", "%d/%m/%y %H:%M")
    >>> dt
    datetime.datetime(2006, 11, 21, 16, 30)
    >>> # Using datetime.timetuple() to get tuple of all attributes
    >>> tt = dt.timetuple()
    >>> for it in tt:
    ...     print(it)
    ...
    2006    # year
    11      # month
    21      # day
    16      # hour
    30      # minute
    0       # second
    1       # weekday (0 = Monday)
    325     # number of days since 1st January
    -1      # dst - method tzinfo.dst() returned None
    >>> # Date in ISO format
    >>> ic = dt.isocalendar()
    >>> for it in ic:
    ...     print(it)
    ...
    2006    # ISO year
    47      # ISO week
    2       # ISO weekday
    >>> # Formatting datetime
    >>> dt.strftime("%A, %d. %B %Y %I:%M%p")
    'Tuesday, 21. November 2006 04:30PM'
    >>> 'The {1} is {0:%d}, the {2} is {0:%B}, the {3} is {0:%I:%M%p}.'.format(dt, "day", "month", "time")
    'The day is 21, the month is November, the time is 04:30PM.'

Using datetime with tzinfo:

    >>> from datetime import timedelta, datetime, tzinfo, timezone
    >>> class KabulTz(tzinfo):
    ...     # Kabul used +4 until 1945, when they moved to +4:30
    ...     UTC_MOVE_DATE = datetime(1944, 12, 31, 20, tzinfo=timezone.utc)
    ...     def utcoffset(self, dt):
    ...         if dt.year < 1945:
    ...             return timedelta(hours=4)
    ...         elif (1945, 1, 1, 0, 0) <= dt.timetuple()[:5] < (1945, 1, 1, 0, 30):
    ...             # If dt falls in the imaginary range, use fold to decide how
    ...             # to resolve. See PEP495
    ...             return timedelta(hours=4, minutes=(30 if dt.fold else 0))
    ...         else:
    ...             return timedelta(hours=4, minutes=30)
    ...
    ...     def fromutc(self, dt):
    ...         # A custom implementation is required for fromutc as
    ...         # the input to this function is a datetime with utc values
    ...         # but with a tzinfo set to self
    ...         # See datetime.astimezone or fromtimestamp
    ...
    ...         # Follow same validations as in datetime.tzinfo
    ...         if not isinstance(dt, datetime):
    ...             raise TypeError("fromutc() requires a datetime argument")
    ...         if dt.tzinfo is not self:
    ...             raise ValueError("dt.tzinfo is not self")
    ...
    ...         if dt.replace(tzinfo=timezone.utc) >= self.UTC_MOVE_DATE:
    ...             return dt + timedelta(hours=4, minutes=30)
    ...         else:
    ...             return dt + timedelta(hours=4)
    ...
    ...     def dst(self, dt):
    ...         return timedelta(0)
    ...
    ...     def tzname(self, dt):
    ...         if dt >= self.UTC_MOVE_DATE:
    ...             return "+04:30"
    ...         else:
    ...             return "+04"
    ...
    ...     def  __repr__(self):
    ...         return f"{self.__class__.__name__}()"
    ...
    >>> tz1 = KabulTz()
    >>> # Datetime before the change
    >>> dt1 = datetime(1900, 11, 21, 16, 30, tzinfo=tz1)
    >>> print(dt1.utcoffset())
    4:00:00
    >>> # Datetime after the change
    >>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
    >>> print(dt2.utcoffset())
    4:30:00
    >>> # Convert datetime to another time zone
    >>> dt3 = dt2.astimezone(timezone.utc)
    >>> dt3
    datetime.datetime(2006, 6, 14, 8, 30, tzinfo=datetime.timezone.utc)
    >>> dt2
    datetime.datetime(2006, 6, 14, 13, 0, tzinfo=KabulTz())
    >>> dt2.utctimetuple() == dt3.utctimetuple()
    True

## `time` Objects

A time object represents a (local) time of day, independent of any particular day, and subject to adjustment via a `tzinfo` object.

class `datetime.``time`(hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)

  All arguments are optional. tzinfo may be `None`, or an instance of a `tzinfo` subclass. The remaining arguments may be integers, in the following ranges:

  - `0 <= hour < 24`,

  - `0 <= minute < 60`,

  - `0 <= second < 60`,

  - `0 <= microsecond < 1000000`,

  - `fold in [0, 1]`.

  If an argument outside those ranges is given, `ValueError` is raised. All default to `0` except tzinfo, which defaults to `None`.

类属性：

`time.``min`

  The earliest representable `time`, `time(0, 0, 0, 0)`.

`time.``max`

  The latest representable `time`, `time(23, 59, 59, 999999)`.

`time.``resolution`

  The smallest possible difference between non-equal `time` objects, `timedelta(microseconds=1)`, although note that arithmetic on `time` objects is not supported.

实例属性（只读）：

`time.``hour`

  In `range(24)`.

`time.``minute`

  In `range(60)`.

`time.``second`

  In `range(60)`.

`time.``microsecond`

  In `range(1000000)`.

`time.``tzinfo`

  The object passed as the tzinfo argument to the `time` constructor, or `None` if none was passed.

`time.``fold`

  In `[0, 1]`. Used to disambiguate wall times during a repeated interval. (A repeated interval occurs when clocks are rolled back at the end of daylight saving time or when the UTC offset for the current zone is decreased for political reasons.) The value 0 (1) represents the earlier (later) of the two moments with the same wall time representation.

  3.6 新版功能.

支持的运算：

- comparison of `time` to `time`, where a is considered less than b when a precedes b in time. If one comparand is naive and the other is aware, `TypeError` is raised if an order comparison is attempted. For equality comparisons, naive instances are never equal to aware instances.

  If both comparands are aware, and have the same `tzinfo` attribute, the common `tzinfo` attribute is ignored and the base times are compared. If both comparands are aware and have different `tzinfo` attributes, the comparands are first adjusted by subtracting their UTC offsets (obtained from `self.utcoffset()`). In order to stop mixed-type comparisons from falling back to the default comparison by object address, when a `time` object is compared to an object of a different type, `TypeError` is raised unless the comparison is `==` or `!=`. The latter cases return `False` or `True`, respectively.

  在 3.3 版更改: Equality comparisons between naive and aware `time` instances don't raise `TypeError`.

- hash, use as dict key

- efficient pickling

In boolean contexts, a `time` object is always considered to be true.

在 3.5 版更改: Before Python 3.5, a `time` object was considered to be false if it represented midnight in UTC. This behavior was considered obscure and error-prone and has been removed in Python 3.5. See bpo-13936 for full details.

Other constructor:

classmethod `time.``fromisoformat`(time_string)

  Return a `time` corresponding to a time_string in one of the formats emitted by `time.isoformat()`. Specifically, this function supports strings in the format(s) `HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]`.

  警告

  This does not support parsing arbitrary ISO 8601 strings - it is only intended as the inverse operation of `time.isoformat()`.

  3.7 新版功能.

实例方法：

`time.``replace`(hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, * fold=0)

  Return a `time` with the same value, except for those attributes given new values by whichever keyword arguments are specified. Note that `tzinfo=None` can be specified to create a naive `time` from an aware `time`, without conversion of the time data.

  3.6 新版功能: 增加了 `fold` 参数。

`time.``isoformat`(timespec='auto')

  Return a string representing the time in ISO 8601 format, HH:MM:SS.ffffff or, if `microsecond` is 0, HH:MM:SS If `utcoffset()` does not return `None`, a string is appended, giving the UTC offset: HH:MM:SS.ffffff+HH:MM[:SS[.ffffff]] or, if self.microsecond is 0, HH:MM:SS+HH:MM[:SS[.ffffff]].

  The optional argument timespec specifies the number of additional components of the time to include (the default is `'auto'`). It can be one of the following:

  - `'auto'`: Same as `'seconds'` if `microsecond` is 0, same as `'microseconds'` otherwise.

  - `'hours'`: Include the `hour` in the two-digit HH format.

  - `'minutes'`: Include `hour` and `minute` in HH:MM format.

  - `'seconds'`: Include `hour`, `minute`, and `second` in HH:MM:SS format.

  - `'milliseconds'`: Include full time, but truncate fractional second part to milliseconds. HH:MM:SS.sss format.

  - `'microseconds'`: Include full time in HH:MM:SS.ffffff format.

  注解

  Excluded time components are truncated, not rounded.

  `ValueError` will be raised on an invalid timespec argument.

      >>> from datetime import time
      >>> time(hour=12, minute=34, second=56, microsecond=123456).isoformat(timespec='minutes')
      '12:34'
      >>> dt = time(hour=12, minute=34, second=56, microsecond=0)
      >>> dt.isoformat(timespec='microseconds')
      '12:34:56.000000'
      >>> dt.isoformat(timespec='auto')
      '12:34:56'

  3.6 新版功能: Added the timespec argument.

`time.``__str__`()

  For a time t, `str(t)` is equivalent to `t.isoformat()`.

`time.``strftime`(format)

  Return a string representing the time, controlled by an explicit format string. For a complete list of formatting directives, see strftime() and strptime() Behavior.

`time.``__format__`(format)

  Same as `time.strftime()`. This makes it possible to specify a format string for a `time` object in formatted string literals and when using `str.format()`. For a complete list of formatting directives, see strftime() and strptime() Behavior.

`time.``utcoffset`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.utcoffset(None)`, and raises an exception if the latter doesn't return `None` or a `timedelta` object with magnitude less than one day.

  在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

`time.``dst`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.dst(None)`, and raises an exception if the latter doesn't return `None`, or a `timedelta` object with magnitude less than one day.

  在 3.7 版更改: The DST offset is not restricted to a whole number of minutes.

`time.``tzname`()

  If `tzinfo` is `None`, returns `None`, else returns `self.tzinfo.tzname(None)`, or raises an exception if the latter doesn't return `None` or a string object.

示例:

    >>> from datetime import time, tzinfo, timedelta
    >>> class TZ1(tzinfo):
    ...     def utcoffset(self, dt):
    ...         return timedelta(hours=1)
    ...     def dst(self, dt):
    ...         return timedelta(0)
    ...     def tzname(self,dt):
    ...         return "+01:00"
    ...     def  __repr__(self):
    ...         return f"{self.__class__.__name__}()"
    ...
    >>> t = time(12, 10, 30, tzinfo=TZ1())
    >>> t
    datetime.time(12, 10, 30, tzinfo=TZ1())
    >>> t.isoformat()
    '12:10:30+01:00'
    >>> t.dst()
    datetime.timedelta(0)
    >>> t.tzname()
    '+01:00'
    >>> t.strftime("%H:%M:%S %Z")
    '12:10:30 +01:00'
    >>> 'The {} is {:%H:%M}.'.format("time", t)
    'The time is 12:10.'

## `tzinfo` 对象

class `datetime.``tzinfo`

  This is an abstract base class, meaning that this class should not be instantiated directly. You need to derive a concrete subclass, and (at least) supply implementations of the standard `tzinfo` methods needed by the `datetime` methods you use. The `datetime` module supplies a simple concrete subclass of `tzinfo`, `timezone`, which can represent timezones with fixed offset from UTC such as UTC itself or North American EST and EDT.

  An instance of (a concrete subclass of) `tzinfo` can be passed to the constructors for `datetime` and `time` objects. The latter objects view their attributes as being in local time, and the `tzinfo` object supports methods revealing offset of local time from UTC, the name of the time zone, and DST offset, all relative to a date or time object passed to them.

  Special requirement for pickling: A `tzinfo` subclass must have an `__init__()` method that can be called with no arguments, else it can be pickled but possibly not unpickled again. This is a technical requirement that may be relaxed in the future.

  A concrete subclass of `tzinfo` may need to implement the following methods. Exactly which methods are needed depends on the uses made of aware `datetime` objects. If in doubt, simply implement all of them.

`tzinfo.``utcoffset`(dt)

  Return offset of local time from UTC, as a `timedelta` object that is positive east of UTC. If local time is west of UTC, this should be negative. Note that this is intended to be the total offset from UTC; for example, if a `tzinfo` object represents both time zone and DST adjustments, `utcoffset()` should return their sum. If the UTC offset isn't known, return `None`. Else the value returned must be a `timedelta` object strictly between `-timedelta(hours=24)` and `timedelta(hours=24)` (the magnitude of the offset must be less than one day). Most implementations of `utcoffset()` will probably look like one of these two:

      return CONSTANT                 # fixed-offset class
      return CONSTANT + self.dst(dt)  # daylight-aware class

  If `utcoffset()` does not return `None`, `dst()` should not return `None` either.

  The default implementation of `utcoffset()` raises `NotImplementedError`.

  在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

`tzinfo.``dst`(dt)

  Return the daylight saving time (DST) adjustment, as a `timedelta` object or `None` if DST information isn't known. Return `timedelta(0)` if DST is not in effect. If DST is in effect, return the offset as a `timedelta` object (see `utcoffset()` for details). Note that DST offset, if applicable, has already been added to the UTC offset returned by `utcoffset()`, so there's no need to consult `dst()` unless you're interested in obtaining DST info separately. For example, `datetime.timetuple()` calls its `tzinfo` attribute's `dst()` method to determine how the `tm_isdst` flag should be set, and `tzinfo.fromutc()` calls `dst()` to account for DST changes when crossing time zones.

  An instance tz of a `tzinfo` subclass that models both standard and daylight times must be consistent in this sense:

  `tz.utcoffset(dt) - tz.dst(dt)`

  must return the same result for every `datetime` dt with `dt.tzinfo == tz` For sane `tzinfo` subclasses, this expression yields the time zone's "standard offset", which should not depend on the date or the time, but only on geographic location. The implementation of `datetime.astimezone()` relies on this, but cannot detect violations; it's the programmer's responsibility to ensure it. If a `tzinfo` subclass cannot guarantee this, it may be able to override the default implementation of `tzinfo.fromutc()` to work correctly with `astimezone()` regardless.

  Most implementations of `dst()` will probably look like one of these two:

      def dst(self, dt):
          # a fixed-offset class:  doesn't account for DST
          return timedelta(0)

  or

      def dst(self, dt):
          # Code to set dston and dstoff to the time zone's DST
          # transition times based on the input dt.year, and expressed
          # in standard local time.  Then

          if dston <= dt.replace(tzinfo=None) < dstoff:
              return timedelta(hours=1)
          else:
              return timedelta(0)

  The default implementation of `dst()` raises `NotImplementedError`.

  在 3.7 版更改: The DST offset is not restricted to a whole number of minutes.

`tzinfo.``tzname`(dt)

  Return the time zone name corresponding to the `datetime` object dt, as a string. Nothing about string names is defined by the `datetime` module, and there's no requirement that it mean anything in particular. For example, "GMT", "UTC", "-500", "-5:00", "EDT", "US/Eastern", "America/New York" are all valid replies. Return `None` if a string name isn't known. Note that this is a method rather than a fixed string primarily because some `tzinfo` subclasses will wish to return different names depending on the specific value of dt passed, especially if the `tzinfo` class is accounting for daylight time.

  The default implementation of `tzname()` raises `NotImplementedError`.

These methods are called by a `datetime` or `time` object, in response to their methods of the same names. A `datetime` object passes itself as the argument, and a `time` object passes `None` as the argument. A `tzinfo` subclass's methods should therefore be prepared to accept a dt argument of `None`, or of class `datetime`.

When `None` is passed, it's up to the class designer to decide the best response. For example, returning `None` is appropriate if the class wishes to say that time objects don't participate in the `tzinfo` protocols. It may be more useful for `utcoffset(None)` to return the standard UTC offset, as there is no other convention for discovering the standard offset.

When a `datetime` object is passed in response to a `datetime` method, `dt.tzinfo` is the same object as self. `tzinfo` methods can rely on this, unless user code calls `tzinfo` methods directly. The intent is that the `tzinfo` methods interpret dt as being in local time, and not need worry about objects in other timezones.

There is one more `tzinfo` method that a subclass may wish to override:

`tzinfo.``fromutc`(dt)

  This is called from the default `datetime.astimezone()` implementation. When called from that, `dt.tzinfo` is self, and dt's date and time data are to be viewed as expressing a UTC time. The purpose of `fromutc()` is to adjust the date and time data, returning an equivalent datetime in self's local time.

  Most `tzinfo` subclasses should be able to inherit the default `fromutc()` implementation without problems. It's strong enough to handle fixed-offset time zones, and time zones accounting for both standard and daylight time, and the latter even if the DST transition times differ in different years. An example of a time zone the default `fromutc()` implementation may not handle correctly in all cases is one where the standard offset (from UTC) depends on the specific date and time passed, which can happen for political reasons. The default implementations of `astimezone()` and `fromutc()` may not produce the result you want if the result is one of the hours straddling the moment the standard offset changes.

  Skipping code for error cases, the default `fromutc()` implementation acts like:

      def fromutc(self, dt):
          # raise ValueError error if dt.tzinfo is not self
          dtoff = dt.utcoffset()
          dtdst = dt.dst()
          # raise ValueError if dtoff is None or dtdst is None
          delta = dtoff - dtdst  # this is self's standard offset
          if delta:
              dt += delta   # convert to standard local time
              dtdst = dt.dst()
              # raise ValueError if dtdst is None
          if dtdst:
              return dt + dtdst
          else:
              return dt

In the following `tzinfo_examples.py` file there are some examples of `tzinfo` classes:

    from datetime import tzinfo, timedelta, datetime

    ZERO = timedelta(0)
    HOUR = timedelta(hours=1)
    SECOND = timedelta(seconds=1)

    # A class capturing the platform's idea of local time.
    # (May result in wrong values on historical times in
    #  timezones where UTC offset and/or the DST rules had
    #  changed in the past.)
    import time as _time

    STDOFFSET = timedelta(seconds = -_time.timezone)
    if _time.daylight:
        DSTOFFSET = timedelta(seconds = -_time.altzone)
    else:
        DSTOFFSET = STDOFFSET

    DSTDIFF = DSTOFFSET - STDOFFSET

    class LocalTimezone(tzinfo):

        def fromutc(self, dt):
            assert dt.tzinfo is self
            stamp = (dt - datetime(1970, 1, 1, tzinfo=self)) // SECOND
            args = _time.localtime(stamp)[:6]
            dst_diff = DSTDIFF // SECOND
            # Detect fold
            fold = (args == _time.localtime(stamp - dst_diff))
            return datetime(*args, microsecond=dt.microsecond,
                            tzinfo=self, fold=fold)

        def utcoffset(self, dt):
            if self._isdst(dt):
                return DSTOFFSET
            else:
                return STDOFFSET

        def dst(self, dt):
            if self._isdst(dt):
                return DSTDIFF
            else:
                return ZERO

        def tzname(self, dt):
            return _time.tzname[self._isdst(dt)]

        def _isdst(self, dt):
            tt = (dt.year, dt.month, dt.day,
                  dt.hour, dt.minute, dt.second,
                  dt.weekday(), 0, 0)
            stamp = _time.mktime(tt)
            tt = _time.localtime(stamp)
            return tt.tm_isdst > 0

    Local = LocalTimezone()

    # A complete implementation of current DST rules for major US time zones.

    def first_sunday_on_or_after(dt):
        days_to_go = 6 - dt.weekday()
        if days_to_go:
            dt += timedelta(days_to_go)
        return dt

    # US DST Rules
    #
    # This is a simplified (i.e., wrong for a few cases) set of rules for US
    # DST start and end times. For a complete and up-to-date set of DST rules
    # and timezone definitions, visit the Olson Database (or try pytz):
    # http://www.twinsun.com/tz/tz-link.htm
    # http://sourceforge.net/projects/pytz/ (might not be up-to-date)
    #
    # In the US, since 2007, DST starts at 2am (standard time) on the second
    # Sunday in March, which is the first Sunday on or after Mar 8.
    DSTSTART_2007 = datetime(1, 3, 8, 2)
    # and ends at 2am (DST time) on the first Sunday of Nov.
    DSTEND_2007 = datetime(1, 11, 1, 2)
    # From 1987 to 2006, DST used to start at 2am (standard time) on the first
    # Sunday in April and to end at 2am (DST time) on the last
    # Sunday of October, which is the first Sunday on or after Oct 25.
    DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
    DSTEND_1987_2006 = datetime(1, 10, 25, 2)
    # From 1967 to 1986, DST used to start at 2am (standard time) on the last
    # Sunday in April (the one on or after April 24) and to end at 2am (DST time)
    # on the last Sunday of October, which is the first Sunday
    # on or after Oct 25.
    DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
    DSTEND_1967_1986 = DSTEND_1987_2006

    def us_dst_range(year):
        # Find start and end times for US DST. For years before 1967, return
        # start = end for no DST.
        if 2006 < year:
            dststart, dstend = DSTSTART_2007, DSTEND_2007
        elif 1986 < year < 2007:
            dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
        elif 1966 < year < 1987:
            dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
        else:
            return (datetime(year, 1, 1), ) * 2

        start = first_sunday_on_or_after(dststart.replace(year=year))
        end = first_sunday_on_or_after(dstend.replace(year=year))
        return start, end

    class USTimeZone(tzinfo):

        def __init__(self, hours, reprname, stdname, dstname):
            self.stdoffset = timedelta(hours=hours)
            self.reprname = reprname
            self.stdname = stdname
            self.dstname = dstname

        def __repr__(self):
            return self.reprname

        def tzname(self, dt):
            if self.dst(dt):
                return self.dstname
            else:
                return self.stdname

        def utcoffset(self, dt):
            return self.stdoffset + self.dst(dt)

        def dst(self, dt):
            if dt is None or dt.tzinfo is None:
                # An exception may be sensible here, in one or both cases.
                # It depends on how you want to treat them.  The default
                # fromutc() implementation (called by the default astimezone()
                # implementation) passes a datetime with dt.tzinfo is self.
                return ZERO
            assert dt.tzinfo is self
            start, end = us_dst_range(dt.year)
            # Can't compare naive to aware objects, so strip the timezone from
            # dt first.
            dt = dt.replace(tzinfo=None)
            if start + HOUR <= dt < end - HOUR:
                # DST is in effect.
                return HOUR
            if end - HOUR <= dt < end:
                # Fold (an ambiguous hour): use dt.fold to disambiguate.
                return ZERO if dt.fold else HOUR
            if start <= dt < start + HOUR:
                # Gap (a non-existent hour): reverse the fold rule.
                return HOUR if dt.fold else ZERO
            # DST is off.
            return ZERO

        def fromutc(self, dt):
            assert dt.tzinfo is self
            start, end = us_dst_range(dt.year)
            start = start.replace(tzinfo=self)
            end = end.replace(tzinfo=self)
            std_time = dt + self.stdoffset
            dst_time = std_time + HOUR
            if end <= dst_time < end + HOUR:
                # Repeated hour
                return std_time.replace(fold=1)
            if std_time < start or dst_time >= end:
                # Standard time
                return std_time
            if start <= std_time < end - HOUR:
                # Daylight saving time
                return dst_time

    Eastern  = USTimeZone(-5, "Eastern",  "EST", "EDT")
    Central  = USTimeZone(-6, "Central",  "CST", "CDT")
    Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
    Pacific  = USTimeZone(-8, "Pacific",  "PST", "PDT")

Note that there are unavoidable subtleties twice per year in a `tzinfo` subclass accounting for both standard and daylight time, at the DST transition points. For concreteness, consider US Eastern (UTC -0500), where EDT begins the minute after 1:59 (EST) on the second Sunday in March, and ends the minute after 1:59 (EDT) on the first Sunday in November:

      UTC   3:MM  4:MM  5:MM  6:MM  7:MM  8:MM
      EST  22:MM 23:MM  0:MM  1:MM  2:MM  3:MM
      EDT  23:MM  0:MM  1:MM  2:MM  3:MM  4:MM

    start  22:MM 23:MM  0:MM  1:MM  3:MM  4:MM

      end  23:MM  0:MM  1:MM  1:MM  2:MM  3:MM

When DST starts (the "start" line), the local wall clock leaps from 1:59 to 3:00. A wall time of the form 2:MM doesn't really make sense on that day, so `astimezone(Eastern)` won't deliver a result with `hour == 2` on the day DST begins. For example, at the Spring forward transition of 2016, we get

    >>> from datetime import datetime, timezone
    >>> from tzinfo_examples import HOUR, Eastern
    >>> u0 = datetime(2016, 3, 13, 5, tzinfo=timezone.utc)
    >>> for i in range(4):
    ...     u = u0 + i*HOUR
    ...     t = u.astimezone(Eastern)
    ...     print(u.time(), 'UTC =', t.time(), t.tzname())
    ...
    05:00:00 UTC = 00:00:00 EST
    06:00:00 UTC = 01:00:00 EST
    07:00:00 UTC = 03:00:00 EDT
    08:00:00 UTC = 04:00:00 EDT

When DST ends (the "end" line), there's a potentially worse problem: there's an hour that can't be spelled unambiguously in local wall time: the last hour of daylight time. In Eastern, that's times of the form 5:MM UTC on the day daylight time ends. The local wall clock leaps from 1:59 (daylight time) back to 1:00 (standard time) again. Local times of the form 1:MM are ambiguous. `astimezone()` mimics the local clock's behavior by mapping two adjacent UTC hours into the same local hour then. In the Eastern example, UTC times of the form 5:MM and 6:MM both map to 1:MM when converted to Eastern, but earlier times have the `fold` attribute set to 0 and the later times have it set to 1. For example, at the Fall back transition of 2016, we get

    >>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
    >>> for i in range(4):
    ...     u = u0 + i*HOUR
    ...     t = u.astimezone(Eastern)
    ...     print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
    ...
    04:00:00 UTC = 00:00:00 EDT 0
    05:00:00 UTC = 01:00:00 EDT 0
    06:00:00 UTC = 01:00:00 EST 1
    07:00:00 UTC = 02:00:00 EST 0

Note that the `datetime` instances that differ only by the value of the `fold` attribute are considered equal in comparisons.

Applications that can't bear wall-time ambiguities should explicitly check the value of the `fold` attribute or avoid using hybrid `tzinfo` subclasses; there are no ambiguities when using `timezone`, or any other fixed-offset `tzinfo` subclass (such as a class representing only EST (fixed offset -5 hours), or only EDT (fixed offset -4 hours)).

参见

dateutil.tz

  The standard library has `timezone` class for handling arbitrary fixed offsets from UTC and `timezone.utc` as UTC timezone instance.

  dateutil.tz library brings the IANA timezone database (also known as the Olson database) to Python and its usage is recommended.

IANA timezone database

  The Time Zone Database (often called tz, tzdata or zoneinfo) contains code and data that represent the history of local time for many representative locations around the globe. It is updated periodically to reflect changes made by political bodies to time zone boundaries, UTC offsets, and daylight-saving rules.

## `timezone` Objects

The `timezone` class is a subclass of `tzinfo`, each instance of which represents a timezone defined by a fixed offset from UTC. Note that objects of this class cannot be used to represent timezone information in the locations where different offsets are used in different days of the year or where historical changes have been made to civil time.

class `datetime.``timezone`(offset, name=None)

  The offset argument must be specified as a `timedelta` object representing the difference between the local time and UTC. It must be strictly between `-timedelta(hours=24)` and `timedelta(hours=24)`, otherwise `ValueError` is raised.

  The name argument is optional. If specified it must be a string that will be used as the value returned by the `datetime.tzname()` method.

  3.2 新版功能.

  在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

`timezone.``utcoffset`(dt)

  Return the fixed value specified when the `timezone` instance is constructed. The dt argument is ignored. The return value is a `timedelta` instance equal to the difference between the local time and UTC.

  在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

`timezone.``tzname`(dt)

  Return the fixed value specified when the `timezone` instance is constructed. If name is not provided in the constructor, the name returned by `tzname(dt)` is generated from the value of the `offset` as follows. If offset is `timedelta(0)`, the name is "UTC", otherwise it is a string 'UTC±HH:MM', where ± is the sign of `offset`, HH and MM are two digits of `offset.hours` and `offset.minutes` respectively.

  在 3.6 版更改: Name generated from `offset=timedelta(0)` is now plain 'UTC', not 'UTC+00:00'.

`timezone.``dst`(dt)

  Always returns `None`.

`timezone.``fromutc`(dt)

  Return `dt + offset`. The dt argument must be an aware `datetime` instance, with `tzinfo` set to `self`.

类属性：

`timezone.``utc`

  The UTC timezone, `timezone(timedelta(0))`.

## `strftime()` and `strptime()` Behavior

`date`, `datetime`, and `time` objects all support a `strftime(format)` method, to create a string representing the time under the control of an explicit format string. Broadly speaking, `d.strftime(fmt)` acts like the `time` module's `time.strftime(fmt, d.timetuple())` although not all objects support a `timetuple()` method.

Conversely, the `datetime.strptime()` class method creates a `datetime` object from a string representing a date and time and a corresponding format string. `datetime.strptime(date_string, format)` is equivalent to `datetime(*(time.strptime(date_string, format)[0:6]))`, except when the format includes sub-second components or timezone offset information, which are supported in `datetime.strptime` but are discarded by `time.strptime`.

For `time` objects, the format codes for year, month, and day should not be used, as time objects have no such values. If they're used anyway, `1900` is substituted for the year, and `1` for the month and day.

For `date` objects, the format codes for hours, minutes, seconds, and microseconds should not be used, as `date` objects have no such values. If they're used anyway, `0` is substituted for them.

For the `datetime.strptime()` class method, the default value is `1900-01-01T00:00:00.000`: any components not specified in the format string will be pulled from the default value. 2

The full set of format codes supported varies across platforms, because Python calls the platform C library's `strftime()` function, and platform variations are common. To see the full set of format codes supported on your platform, consult the strftime(3) documentation.

For the same reason, handling of format strings containing Unicode code points that can't be represented in the charset of the current locale is also platform-dependent. On some platforms such code points are preserved intact in the output, while on others `strftime` may raise `UnicodeError` or return an empty string instead.

The following is a list of all the format codes that the C standard (1989 version) requires, and these work on all platforms with a standard C implementation. Note that the 1999 version of the C standard added additional format codes.

指令 | 意义 | 示例 | 注释
--- | --- | --- | ---
`%a` | 当地工作日的缩写。 | Sun, Mon, ..., Sat (美国); So, Mo, ..., Sa (德国) | (1)
`%A` | 当地工作日的全名。 | Sunday, Monday, ..., Saturday (美国); Sonntag, Montag, ..., Samstag (德国) | (1)
`%w` | 以十进制数显示的工作日，其中0表示星期日，6表示星期六。 | 0, 1, ..., 6 |
`%d` | 补零后，以十进制数显示的月份中的一天。 | 01, 02, ..., 31 | (9)
`%b` | 当地月份的缩写。 | Jan, Feb, ..., Dec (美国); Jan, Feb, ..., Dez (德国) | (1)
`%B` | 当地月份的全名。 | January, February, ..., December (美国); Januar, Februar, ..., Dezember (德国) | (1)
`%m` | 补零后，以十进制数显示的月份。 | 01, 02, ..., 12 | (9)
`%y` | 补零后，以十进制数表示的，不带世纪的年份。 | 00, 01, ..., 99 | (9)
`%Y` | 十进制数表示的带世纪的年份。 | 0001, 0002, ..., 2013, 2014, ..., 9998, 9999 | (2)
`%H` | Hour (24-hour clock) as a zero-padded decimal number. | 00, 01, ..., 23 | (9)
`%I` | Hour (12-hour clock) as a zero-padded decimal number. | 01, 02, ..., 12 | (9)
`%p` | 本地化的 AM 或 PM 。 | AM, PM (美国); am, pm (德国) | (1), (3)
`%M` | 补零后，以十进制数显示的分钟。 | 00, 01, ..., 59 | (9)
`%S` | 补零后，以十进制数显示的秒。 | 00, 01, ..., 59 | (4), (9)
`%f` | Microsecond as a decimal number, zero-padded on the left. | 000000, 000001, ..., 999999 | (5)
`%z` | UTC offset in the form ±HHMM[SS[.ffffff]] (empty string if the object is naive). | (empty), +0000, -0400, +1030, +063415, -030712.345216 | (6)
`%Z` | Time zone name (empty string if the object is naive). | (empty), UTC, EST, CST |
`%j` | Day of the year as a zero-padded decimal number. | 001, 002, ..., 366 | (9)
`%U` | Week number of the year (Sunday as the first day of the week) as a zero padded decimal number. All days in a new year preceding the first Sunday are considered to be in week 0. | 00, 01, ..., 53 | (7), (9)
`%W` | Week number of the year (Monday as the first day of the week) as a decimal number. All days in a new year preceding the first Monday are considered to be in week 0. | 00, 01, ..., 53 | (7), (9)
`%c` | 本地化的适当日期和时间表示。 | Tue Aug 16 21:30:00 1988 (美国); Di 16 Aug 21:30:00 1988 (德国) | (1)
`%x` | 本地化的适当日期表示。 | 08/16/88 (None); 08/16/1988 (en_US); 16.08.1988 (de_DE) | (1)
`%X` | 本地化的适当时间表示。 | 21:30:00 (en_US); 21:30:00 (de_DE) | (1)
`%%` | 字面的 `'%'` 字符。 | % |

Several additional directives not required by the C89 standard are included for convenience. These parameters all correspond to ISO 8601 date values. These may not be available on all platforms when used with the `strftime()` method. The ISO 8601 year and ISO 8601 week directives are not interchangeable with the year and week number directives above. Calling `strptime()` with incomplete or ambiguous ISO 8601 directives will raise a `ValueError`.

指令 | 意义 | 示例 | 注释
--- | --- | --- | ---
`%G` | ISO 8601 year with century representing the year that contains the greater part of the ISO week (`%V`). | 0001, 0002, ..., 2013, 2014, ..., 9998, 9999 | (8)
`%u` | ISO 8601 weekday as a decimal number where 1 is Monday. | 1, 2, ..., 7 |
`%V` | ISO 8601 week as a decimal number with Monday as the first day of the week. Week 01 is the week containing Jan 4. | 01, 02, ..., 53 | (8), (9)

3.6 新版功能: 增加了 `%G`, `%u` 和 `%V`。

注释:

1. Because the format depends on the current locale, care should be taken when making assumptions about the output value. Field orderings will vary (for example, "month/day/year" versus "day/month/year"), and the output may contain Unicode characters encoded using the locale's default encoding (for example, if the current locale is `ja_JP`, the default encoding could be any one of `eucJP`, `SJIS`, or `utf-8`; use `locale.getlocale()` to determine the current locale's encoding).

2. The `strptime()` method can parse years in the full [1, 9999] range, but years < 1000 must be zero-filled to 4-digit width.

   在 3.2 版更改: In previous versions, `strftime()` method was restricted to years >= 1900.

   在 3.3 版更改: 在版本3.2中，`strftime()` 方法只限于 years >= 1000。

3. When used with the `strptime()` method, the `%p` directive only affects the output hour field if the `%I` directive is used to parse the hour.

4. 与 `time` 模块不同的是， `datetime` 模块不支持闰秒。

5. When used with the `strptime()` method, the `%f` directive accepts from one to six digits and zero pads on the right. `%f` is an extension to the set of format characters in the C standard (but implemented separately in datetime objects, and therefore always available).

6. For a naive object, the `%z` and `%Z` format codes are replaced by empty strings.

   对于一个觉悟型对象而言：

   `%z`

     `utcoffset()` is transformed into a string of the form ±HHMM[SS[.ffffff]], where HH is a 2-digit string giving the number of UTC offset hours, MM is a 2-digit string giving the number of UTC offset minutes, SS is a 2-digit string giving the number of UTC offset seconds and ffffff is a 6-digit string giving the number of UTC offset microseconds. The ffffff part is omitted when the offset is a whole number of seconds and both the ffffff and the SS part is omitted when the offset is a whole number of minutes. For example, if `utcoffset()` returns `timedelta(hours=-3, minutes=-30)`, `%z` is replaced with the string `'-0330'`.

   在 3.7 版更改: The UTC offset is not restricted to a whole number of minutes.

   在 3.7 版更改: When the `%z` directive is provided to the `strptime()` method, the UTC offsets can have a colon as a separator between hours, minutes and seconds. For example, `'+01:00:00'` will be parsed as an offset of one hour. In addition, providing `'Z'` is identical to `'+00:00'`.

   `%Z`

     If `tzname()` returns `None`, `%Z` is replaced by an empty string. Otherwise `%Z` is replaced by the returned value, which must be a string.

   在 3.2 版更改: When the `%z` directive is provided to the `strptime()` method, an aware `datetime` object will be produced. The `tzinfo` of the result will be set to a `timezone` instance.

7. When used with the `strptime()` method, `%U` and `%W` are only used in calculations when the day of the week and the calendar year (`%Y`) are specified.

8. Similar to `%U` and `%W`, `%V` is only used in calculations when the day of the week and the ISO year (`%G`) are specified in a `strptime()` format string. Also note that `%G` and `%Y` are not interchangeable.

9. When used with the `strptime()` method, the leading zero is optional for formats `%d`, `%m`, `%H`, `%I`, `%M`, `%S`, `%J`, `%U`, `%W`, and `%V`. Format `%y` does require a leading zero.

脚注

1

  If, that is, we ignore the effects of Relativity

2

  Passing `datetime.strptime('Feb 29', '%b %d')` will fail since `1900` is not a leap year.