# `datetime` --- 日期與時間的基本型別

原始碼：Lib/datetime.py

`datetime` 模組提供操作日期與時間的類別。

While date and time arithmetic is supported, the focus of the implementation is on efficient attribute extraction for output formatting and manipulation.

小訣竅

跳轉至格式碼 (format codes)。

也參考

`calendar` 模組

  與日曆相關的一般函式。

`time` 模組

  Time access and conversions.

`zoneinfo` 模組

  Concrete time zones representing the IANA time zone database.

dateutil 套件

  帶有時區與剖析擴充支援的第三方函式庫。

DateType 套件

  Third-party library that introduces distinct static types to for example, allow static type checkers to differentiate between naive and aware datetimes.

## Aware and naive objects

Date and time objects may be categorized as "aware" or "naive" depending on whether or not they include time zone information.

With sufficient knowledge of applicable algorithmic and political time adjustments, such as time zone and daylight saving time information, an aware object can locate itself relative to other aware objects. An aware object represents a specific moment in time that is not open to interpretation. [1]

A naive object does not contain enough information to unambiguously locate itself relative to other date/time objects. Whether a naive object represents Coordinated Universal Time (UTC), local time, or time in some other time zone is purely up to the program, just like it is up to the program whether a particular number represents metres, miles, or mass. Naive objects are easy to understand and to work with, at the cost of ignoring some aspects of reality.

For applications requiring aware objects, `datetime` and `time` objects have an optional time zone information attribute, `tzinfo`, that can be set to an instance of a subclass of the abstract `tzinfo` class. These `tzinfo` objects capture information about the offset from UTC time, the time zone name, and whether daylight saving time is in effect.

Only one concrete `tzinfo` class, the `timezone` class, is supplied by the `datetime` module. The `timezone` class can represent simple time zones with fixed offsets from UTC, such as UTC itself or North American EST and EDT time zones. Supporting time zones at deeper levels of detail is up to the application. The rules for time adjustment across the world are more political than rational, change frequently, and there is no standard suitable for every application aside from UTC.

## 常數

`datetime` 模組匯出以下常數：

datetime.MINYEAR

  The smallest year number allowed in a `date` or `datetime` object. `MINYEAR` is 1.

datetime.MAXYEAR

  The largest year number allowed in a `date` or `datetime` object. `MAXYEAR` is 9999.

datetime.UTC

  Alias for the UTC time zone singleton `datetime.timezone.utc`.

  在 3.11 版被加入.

## Available types

class datetime.date

  An idealized naive date, assuming the current Gregorian calendar always was, and always will be, in effect. Attributes: `year`, `month`, and `day`.

class datetime.time

  An idealized time, independent of any particular day, assuming that every day has exactly 24*60*60 seconds. (There is no notion of "leap seconds" here.) Attributes: `hour`, `minute`, `second`, `microsecond`, and `tzinfo`.

class datetime.datetime

  A combination of a date and a time. Attributes: `year`, `month`, `day`, `hour`, `minute`, `second`, `microsecond`, and `tzinfo`.

class datetime.timedelta

  表示兩個 `datetime` 或 `date` 實例之間時間的差異，以微秒為解析度。

class datetime.tzinfo

  An abstract base class for time zone information objects. These are used by the `datetime` and `time` classes to provide a customizable notion of time adjustment (for example, to account for time zone and/or daylight saving time).

class datetime.timezone

  A class that implements the `tzinfo` abstract base class as a fixed offset from the UTC.

  在 3.2 版被加入.

Objects of these types are immutable.

Subclass relationships:

### 常見屬性

The `date`, `datetime`, `time`, and `timezone` types share these common features:

- Objects of these types are immutable.

- Objects of these types are hashable, meaning that they can be used as dictionary keys.

- Objects of these types support efficient pickling via the `pickle` module.

### Determining if an object is aware or naive

Objects of the `date` type are always naive.

An object of type `time` or `datetime` may be aware or naive.

A `datetime` object `d` is aware if both of the following hold:

1. `d.tzinfo` 不是 `None`

2. `d.tzinfo.utcoffset(d)` 不會回傳 `None`

否則 `d` 會是 naive 的。

A `time` object `t` is aware if both of the following hold:

1. `t.tzinfo` 不是 `None`

2. `t.tzinfo.utcoffset(None)` 沒有回傳 `None`。

否則 `t` 會是 naive 的。

The distinction between aware and naive doesn't apply to `timedelta` objects.

## `timedelta` 物件

一個 `timedelta` 物件代表著一段持續時間，即兩個 `datetime` 或 `date` 之間的差異。

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

  All arguments are optional and default to 0. Arguments may be integers or floats, and may be positive or negative.

  Only days, seconds and microseconds are stored internally. Arguments are converted to those units:

  - 一毫秒會被轉換為 1000 微秒。

  - 一分鐘會被轉換為 60 秒。

  - 一小時會被轉換為 3600 秒。

  - 一週會被轉換為 7 天。

  and days, seconds and microseconds are then normalized so that the representation is unique, with

  - `0 <= microseconds < 1000000`

  - `0 <= seconds < 3600*24` (the number of seconds in one day)

  - `-999999999 <= days <= 999999999`

  The following example illustrates how any arguments besides days, seconds and microseconds are "merged" and normalized into those three resulting attributes:

      >>> import datetime as dt
      >>> delta = dt.timedelta(
      ...     days=50,
      ...     seconds=27,
      ...     microseconds=10,
      ...     milliseconds=29000,
      ...     minutes=5,
      ...     hours=8,
      ...     weeks=2
      ... )
      >>> # Only days, seconds, and microseconds remain
      >>> delta
      datetime.timedelta(days=64, seconds=29156, microseconds=10)

  小訣竅

  `import datetime as dt` instead of `import datetime` or `from datetime import datetime` to avoid confusion between the module and the class. See How I Import Python’s datetime Module.

  If any argument is a float and there are fractional microseconds, the fractional microseconds left over from all arguments are combined and their sum is rounded to the nearest microsecond using round-half-to-even tiebreaker. If no argument is a float, the conversion and normalization processes are exact (no information is lost).

  If the normalized value of days lies outside the indicated range, `OverflowError` is raised.

  Note that normalization of negative values may be surprising at first. For example:

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

  Since the string representation of `timedelta` objects can be confusing, use the following recipe to produce a more readable format:

      >>> def pretty_timedelta(td):
      ...     if td.days >= 0:
      ...         return str(td)
      ...     return f'-({-td!s})'
      ...
      >>> d = timedelta(hours=-1)
      >>> str(d)  # not human-friendly
      '-1 day, 23:00:00'
      >>> pretty_timedelta(d)
      '-(1:00:00)'

類別屬性：

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

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

Note that, because of normalization, `timedelta.max` is greater than `-timedelta.min`. `-timedelta.max` is not representable as a `timedelta` object.

Instance attributes (read-only):

timedelta.days

  在 -999,999,999 到 999,999,999 （含）之間

timedelta.seconds

  在 0 到 86,399 （含）之間

  警示

  It is a somewhat common bug for code to unintentionally use this attribute when it is actually intended to get a `total_seconds()` value instead:

      >>> import datetime as dt
      >>> duration = dt.timedelta(seconds=11235813)
      >>> duration.days, duration.seconds
      (130, 3813)
      >>> duration.total_seconds()
      11235813.0

timedelta.microseconds

  在 0 到 999,999 （含）之間

Supported operations:

Operation | Result
--- | ---
`t1 = t2 + t3` | Sum of `t2` and `t3`. Afterwards `t1 - t2 == t3` and `t1 - t3 == t2` are true. (1)
`t1 = t2 - t3` | Difference of `t2` and `t3`. Afterwards `t1 == t2 - t3` and `t2 == t1 + t3` are true. (1)(6)
`t1 = t2 * i or t1 = i * t2` | Delta multiplied by an integer. Afterwards `t1 // i == t2` is true, provided `i != 0`.
| In general, `t1 * i == t1 * (i-1) + t1` is true. (1)
`t1 = t2 * f or t1 = f * t2` | Delta multiplied by a float. The result is rounded to the nearest multiple of timedelta.resolution using round-half-to-even.
`f = t2 / t3` | Division (3) of overall duration `t2` by interval unit `t3`. Returns a `float` object.
`t1 = t2 / f or t1 = t2 / i` | Delta divided by a float or an int. The result is rounded to the nearest multiple of timedelta.resolution using round-half-to-even.
`t1 = t2 // i` or `t1 = t2 // t3` | The floor is computed and the remainder (if any) is thrown away. In the second case, an integer is returned. (3)
`t1 = t2 % t3` | The remainder is computed as a `timedelta` object. (3)
`q, r = divmod(t1, t2)` | Computes the quotient and the remainder: `q = t1 // t2` (3) and `r = t1 % t2`. `q` is an integer and `r` is a `timedelta` object.
`+t1` | Returns a `timedelta` object with the same value. (2)
`-t1` | 等價於 `timedelta(-t1.days, -t1.seconds, -t1.microseconds)`，也等價於 `t1 * -1`。 (1)(4)
`abs(t)` | Equivalent to `+t` when `t.days >= 0`, and to `-t` when `t.days < 0`. (2)
`str(t)` | Returns a string in the form `[D day[s], ][H]H:MM:SS[.UUUUUU]`, where D is negative for negative `t`. (5)
`repr(t)` | Returns a string representation of the `timedelta` object as a constructor call with canonical attribute values.

註解：

1. 這是精確的，但可能會溢位。

2. 這是精確的，且不會溢位。

3. Division by zero raises `ZeroDivisionError`.

4. `-timedelta.max` is not representable as a `timedelta` object.

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. The expression `t2 - t3` will always be equal to the expression `t2 + (-t3)` except when t3 is equal to `timedelta.max`; in that case the former will produce a result while the latter will overflow.

In addition to the operations listed above, `timedelta` objects support certain additions and subtractions with `date` and `datetime` objects (see below).

在 3.2 版的變更: 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.

`timedelta` objects support equality and order comparisons.

In Boolean contexts, a `timedelta` object is considered to be true if and only if it isn't equal to `timedelta(0)`.

實例方法：

timedelta.total_seconds()

  Return the total number of seconds contained in the duration. Equivalent to `td / timedelta(seconds=1)`. For interval units other than seconds, use the division form directly (for example, `td / timedelta(microseconds=1)`).

  Note that for very large time intervals (greater than 270 years on most platforms) this method will lose microsecond accuracy.

  在 3.2 版被加入.

### 用法範例：`timedelta`

An additional example of normalization:

    >>> # Components of another_year add up to exactly 365 days
    >>> import datetime as dt
    >>> year = dt.timedelta(days=365)
    >>> another_year = dt.timedelta(weeks=40, days=84, hours=23,
    ...                             minutes=50, seconds=600)
    >>> year == another_year
    True
    >>> year.total_seconds()
    31536000.0

Examples of `timedelta` arithmetic:

    >>> import datetime as dt
    >>> year = dt.timedelta(days=365)
    >>> ten_years = 10 * year
    >>> ten_years
    datetime.timedelta(days=3650)
    >>> ten_years.days // 365
    10
    >>> nine_years = ten_years - year
    >>> nine_years
    datetime.timedelta(days=3285)
    >>> three_years = nine_years // 3
    >>> three_years, three_years.days // 365
    (datetime.timedelta(days=1095), 3)

## `date` 物件

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. [2]

class datetime.date(year, month, day)

  All arguments are required. Arguments must be integers, in the following ranges:

  - `MINYEAR <= year <= MAXYEAR`

  - `1 <= month <= 12`

  - `1 <= day <= 該年該月的天數`

  If an argument outside those ranges is given, `ValueError` is raised.

Other constructors, all class methods:

classmethod date.today()

  回傳目前的本地日期。

  這等同於 `date.fromtimestamp(time.time())`。

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 版的變更: 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.

  在 3.15 版的變更: Accepts any real number as timestamp, not only integer or float.

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 given in any valid ISO 8601 format, with the following exceptions:

  1. Reduced precision dates are not currently supported (`YYYY-MM`, `YYYY`).

  2. Extended date representations are not currently supported (`±YYYYYY-MM-DD`).

  3. Ordinal dates are not currently supported (`YYYY-OOO`).

  範例：

      >>> import datetime as dt
      >>> dt.date.fromisoformat('2019-12-04')
      datetime.date(2019, 12, 4)
      >>> dt.date.fromisoformat('20191204')
      datetime.date(2019, 12, 4)
      >>> dt.date.fromisoformat('2021-W01-1')
      datetime.date(2021, 1, 4)

  在 3.7 版被加入.

  在 3.11 版的變更: Previously, this method only supported the format `YYYY-MM-DD`.

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()`.

  在 3.8 版被加入.

classmethod date.strptime(date_string, format)

  Return a `date` corresponding to date_string, parsed according to format. This is equivalent to:

      date(*(time.strptime(date_string, format)[0:3]))

  `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. See also strftime() 與 strptime() 的行為 and `date.fromisoformat()`.

  備註

  If format specifies a day of month (`%d`) without a year, `ValueError` is raised. This is to avoid a quadrennial leap year bug in code seeking to parse only a month and day as the default year used in absence of one in the format is not a leap year. The workaround is to always include a year in your format. If parsing date_string values that do not have a year, explicitly add a year that is a leap year before parsing:

      >>> import datetime as dt
      >>> date_string = "02/29"
      >>> when = dt.date.strptime(f"{date_string};1984", "%m/%d;%Y")  # 避免閏年錯誤。
      >>> when.strftime("%B %d")
      'February 29'

  在 3.14 版被加入.

類別屬性：

date.min

  The earliest representable date, `date(MINYEAR, 1, 1)`.

date.max

  The latest representable date, `date(MAXYEAR, 12, 31)`.

date.resolution

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

Instance attributes (read-only):

date.year

  Between `MINYEAR` and `MAXYEAR` inclusive.

date.month

  在 1 到 12 （含）之間。

date.day

  Between 1 and the number of days in the given month of the given year.

Supported operations:

Operation | Result
--- | ---
`date2 = date1 + timedelta` | `date2` will be `timedelta.days` days after `date1`. (1)
`date2 = date1 - timedelta` | Computes `date2` such that `date2 + timedelta == date1`. (2)
`timedelta = date1 - date2` | (3)
`date1 == date2` `date1 != date2` | Equality comparison. (4)
`date1 < date2` `date1 > date2` `date1 <= date2` `date1 >= date2` | Order comparison. (5)

註解：

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` 被忽略。

3. This is exact, and cannot overflow. `timedelta.seconds` and `timedelta.microseconds` are 0, and `date2 + timedelta == date1` after.

4. `date` objects are equal if they represent the same date.

   `date` objects that are not also `datetime` instances are never equal to `datetime` objects, even if they represent the same date.

5. date1 is considered less than date2 when date1 precedes date2 in time. In other words, `date1 < date2` if and only if `date1.toordinal() < date2.toordinal()`.

   Order comparison between a `date` object that is not also a `datetime` instance and a `datetime` object raises `TypeError`.

在 3.13 版的變更: Comparison between `datetime` object and an instance of the `date` subclass that is not a `datetime` subclass no longer converts the latter to `date`, ignoring the time part and the time zone. The default behavior can be changed by overriding the special comparison methods in subclasses.

In Boolean contexts, all `date` objects are considered to be true.

實例方法：

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

  Return a new `date` object with the same values, but with specified parameters updated.

  範例：

      >>> import datetime as dt
      >>> d = dt.date(2002, 12, 31)
      >>> d.replace(day=26)
      datetime.date(2002, 12, 26)

  The generic function `copy.replace()` also supports `date` objects.

date.timetuple()

  回傳一個 `time.struct_time`，如同 `time.localtime()` 所回傳。

  The hours, minutes and seconds are 0, and the DST flag is -1.

  `d.timetuple()` 等價於：

      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()

  回傳一個代表星期幾的整數，星期一為 0、星期日為 6。例如 `date(2002, 12, 4).weekday() == 2` 為星期三。也請參考 `isoweekday()`。

date.isoweekday()

  Return the day of the week as an integer, where Monday is 1 and Sunday is 7. For example, `date(2002, 12, 4).isoweekday() == 3`, a Wednesday. See also `weekday()`, `isocalendar()`.

date.isocalendar()

  Return a named tuple object with three components: `year`, `week` and `weekday`.

  The ISO calendar is a widely used variant of the Gregorian calendar. [3]

  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:

      >>> import datetime as dt
      >>> dt.date(2003, 12, 29).isocalendar()
      datetime.IsoCalendarDate(year=2004, week=1, weekday=1)
      >>> dt.date(2004, 1, 4).isocalendar()
      datetime.IsoCalendarDate(year=2004, week=1, weekday=7)

  在 3.9 版的變更: Result changed from a tuple to a named tuple.

date.isoformat()

  回傳一以 ISO 8601 格式 `YYYY-MM-DD` 表示的日期字串：

      >>> import datetime as dt
      >>> dt.date(2002, 12, 4).isoformat()
      '2002-12-04'

date.__str__()

  For a date `d`, `str(d)` is equivalent to `d.isoformat()`.

date.ctime()

  Return a string representing the date:

      >>> import datetime as dt
      >>> dt.date(2002, 12, 4).ctime()
      'Wed Dec  4 00:00:00 2002'

  `d.ctime()` 等價於：

      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. See also strftime() 與 strptime() 的行為 and `date.isoformat()`.

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()`. See also strftime() 與 strptime() 的行為 and `date.isoformat()`.

### 用法範例：`date`

計算一個事件的天數的範例：

    >>> import time
    >>> import datetime as dt
    >>> today = dt.date.today()
    >>> today
    datetime.date(2007, 12, 5)
    >>> today == dt.date.fromtimestamp(time.time())
    True
    >>> my_birthday = dt.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

更多 `date` 的用法範例：

    >>> import datetime as dt
    >>> d = dt.date.fromordinal(730920) # 730920th day after 1. 1. 0001
    >>> d
    datetime.date(2002, 3, 11)

    >>> # Methods related to formatting string output
    >>> d.isoformat()
    '2002-03-11'
    >>> d.strftime("%d/%m/%y")
    '11/03/02'
    >>> d.strftime("%A %d. %B %Y")
    'Monday 11. March 2002'
    >>> d.ctime()
    'Mon Mar 11 00:00:00 2002'
    >>> 'The {1} is {0:%d}, the {2} is {0:%B}.'.format(d, "day", "month")
    'The day is 11, the month is March.'

    >>> # Methods for extracting 'components' under different calendars
    >>> 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 )

    >>> # A date object is immutable; all operations produce a new object
    >>> d.replace(year=2005)
    datetime.date(2005, 3, 11)

## `datetime` 物件

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.

建構函式：

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

  The year, month and day arguments are required. tzinfo may be `None`, or an instance of a `tzinfo` subclass. The remaining arguments must be integers in the following ranges:

  - `MINYEAR <= year <= MAXYEAR`,

  - `1 <= month <= 12`,

  - `1 <= day <= number of days in the given month and year`,

  - `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.

  在 3.6 版的變更: 新增 fold 參數。

Other constructors, all class methods:

classmethod datetime.today()

  回傳目前的本地日期與時間，且 `tzinfo` 為 `None`。

  等價於：

      datetime.fromtimestamp(time.time())

  也請見 `now()`、`fromtimestamp()`。

  This method is functionally equivalent to `now()`, but without a `tz` parameter.

classmethod datetime.now(tz=None)

  Return the current local date and time.

  如果選用的引數 tz 為 `None` 或未指定，則會像是 `today()`，但盡可能提供比透過 `time.time()` 取得的時間戳記更多位數的資訊（例如，這在有提供 C `gettimeofday()` 函式的平台上可能可行）。

  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.

  This function is preferred over `today()` and `utcnow()`.

  備註

  Subsequent calls to `datetime.now()` may return the same instant depending on the precision of the underlying clock.

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()`.

  警告

  Because naive `datetime` objects are treated by many `datetime` methods as local times, it is preferred to use aware datetimes to represent times in UTC. As such, the recommended way to create an object representing the current time in UTC is by calling `datetime.now(timezone.utc)`.

  在 3.12 版之後被棄用: Use `datetime.now()` with `UTC` instead.

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.

  `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. This method is preferred over `utcfromtimestamp()`.

  在 3.3 版的變更: 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 版的變更: `fromtimestamp()` may return instances with `fold` set to 1.

  在 3.15 版的變更: Accepts any real number as timestamp, not only integer or float.

classmethod datetime.utcfromtimestamp(timestamp)

  Return the UTC `datetime` corresponding to the POSIX timestamp, with `tzinfo` `None`. (The resulting object is naive.)

  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.

  警告

  Because naive `datetime` objects are treated by many `datetime` methods as local times, it is preferred to use aware datetimes to represent times in UTC. As such, the recommended way to create an object representing a specific timestamp in UTC is by calling `datetime.fromtimestamp(timestamp, tz=timezone.utc)`.

  在 3.3 版的變更: 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.

  在 3.15 版的變更: Accepts any real number as timestamp, not only integer or float.

  在 3.12 版之後被棄用: Use `datetime.fromtimestamp()` with `UTC` instead.

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=time.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. If the date argument is a `datetime` object, its time components and `tzinfo` attributes are ignored.

  For any `datetime` object `d`, `d == datetime.combine(d.date(), d.time(), d.tzinfo)`.

  在 3.6 版的變更: 新增 tzinfo 引數。

classmethod datetime.fromisoformat(date_string)

  Return a `datetime` corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:

  1. Time zone offsets may have fractional seconds.

  2. The `T` separator may be replaced by any single unicode character.

  3. Fractional hours and minutes are not supported.

  4. Reduced precision dates are not currently supported (`YYYY-MM`, `YYYY`).

  5. Extended date representations are not currently supported (`±YYYYYY-MM-DD`).

  6. Ordinal dates are not currently supported (`YYYY-OOO`).

  範例：

      >>> import datetime as dt
      >>> dt.datetime.fromisoformat('2011-11-04')
      datetime.datetime(2011, 11, 4, 0, 0)
      >>> dt.datetime.fromisoformat('20111104')
      datetime.datetime(2011, 11, 4, 0, 0)
      >>> dt.datetime.fromisoformat('2011-11-04T00:05:23')
      datetime.datetime(2011, 11, 4, 0, 5, 23)
      >>> dt.datetime.fromisoformat('2011-11-04T00:05:23Z')
      datetime.datetime(2011, 11, 4, 0, 5, 23, tzinfo=datetime.timezone.utc)
      >>> dt.datetime.fromisoformat('20111104T000523')
      datetime.datetime(2011, 11, 4, 0, 5, 23)
      >>> dt.datetime.fromisoformat('2011-W01-2T00:05:23.283')
      datetime.datetime(2011, 1, 4, 0, 5, 23, 283000)
      >>> dt.datetime.fromisoformat('2011-11-04 00:05:23.283')
      datetime.datetime(2011, 11, 4, 0, 5, 23, 283000)
      >>> dt.datetime.fromisoformat('2011-11-04 00:05:23.283+00:00')
      datetime.datetime(2011, 11, 4, 0, 5, 23, 283000, tzinfo=datetime.timezone.utc)
      >>> dt.datetime.fromisoformat('2011-11-04T00:05:23+04:00')
      datetime.datetime(2011, 11, 4, 0, 5, 23,
          tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))

  在 3.7 版被加入.

  在 3.11 版的變更: Previously, this method only supported formats that could be emitted by `date.isoformat()` or `datetime.isoformat()`.

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()`.

  在 3.8 版被加入.

classmethod datetime.strptime(date_string, format)

  Return a `datetime` corresponding to date_string, parsed according to format.

  If format does not contain microseconds or time zone information, 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. See also strftime() 與 strptime() 的行為 and `datetime.fromisoformat()`.

  在 3.15 版的變更: If format specifies a day of month (`%d`) without a year, `ValueError` is raised. This is to avoid a quadrennial leap year bug in code seeking to parse only a month and day as the default year used in absence of one in the format is not a leap year. The workaround is to always include a year in your format. If parsing date_string values that do not have a year, explicitly add a year that is a leap year before parsing:

      >>> import datetime as dt
      >>> date_string = "02/29"
      >>> when = dt.datetime.strptime(f"{date_string};1984", "%m/%d;%Y")  # 避免閏年錯誤。
      >>> when.strftime("%B %d")
      'February 29'

類別屬性：

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)`.

Instance attributes (read-only):

datetime.year

  Between `MINYEAR` and `MAXYEAR` inclusive.

datetime.month

  在 1 到 12 （含）之間。

datetime.day

  Between 1 and the number of days in the given month of the given year.

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 values 0 and 1 represent, respectively, the earlier and later of the two moments with the same wall time representation.

  在 3.6 版被加入.

Supported operations:

Operation | Result
--- | ---
`datetime2 = datetime1 + timedelta` | (1)
`datetime2 = datetime1 - timedelta` | (2)
`timedelta = datetime1 - datetime2` | (3)
`datetime1 == datetime2` `datetime1 != datetime2` | Equality comparison. (4)
`datetime1 < datetime2` `datetime1 > datetime2` `datetime1 <= datetime2` `datetime1 >= datetime2` | Order comparison. (5)

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. The result is `(a.replace(tzinfo=None) - a.utcoffset()) - (b.replace(tzinfo=None) - b.utcoffset())` except that the implementation never overflows.

4. `datetime` objects are equal if they represent the same date and time, taking into account the time zone.

   Naive and aware `datetime` objects are never equal.

   If both comparands are aware, and have the same `tzinfo` attribute, the `tzinfo` and `fold` attributes are ignored and the base datetimes are compared. If both comparands are aware and have different `tzinfo` attributes, the comparison acts as comparands were first converted to UTC datetimes except that the implementation never overflows. `datetime` instances in a repeated interval are never equal to `datetime` instances in other time zone.

5. datetime1 is considered less than datetime2 when datetime1 precedes datetime2 in time, taking into account the time zone.

   Order comparison between naive and aware `datetime` objects raises `TypeError`.

   If both comparands are aware, and have the same `tzinfo` attribute, the `tzinfo` and `fold` attributes are ignored and the base datetimes are compared. If both comparands are aware and have different `tzinfo` attributes, the comparison acts as comparands were first converted to UTC datetimes except that the implementation never overflows.

在 3.3 版的變更: Equality comparisons between aware and naive `datetime` instances don't raise `TypeError`.

在 3.13 版的變更: Comparison between `datetime` object and an instance of the `date` subclass that is not a `datetime` subclass no longer converts the latter to `date`, ignoring the time part and the time zone. The default behavior can be changed by overriding the special comparison methods in subclasses.

實例方法：

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 版的變更: 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 版的變更: 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 new `datetime` object with the same attributes, but with specified parameters updated. Note that `tzinfo=None` can be specified to create a naive datetime from an aware datetime with no conversion of date and time data.

  `datetime` objects are also supported by generic function `copy.replace()`.

  在 3.6 版的變更: 新增 fold 參數。

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 time zone.

  If called without arguments (or with `tz=None`) the system local time zone is assumed for the target time zone. 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 time zone 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 `timezone` 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 `timezone` 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 timezone object.
          utc = (self - self.utcoffset()).replace(tzinfo=tz)
          # Convert from UTC to tz's local time.
          return tz.fromutc(utc)

  在 3.3 版的變更: tz now can be omitted.

  在 3.6 版的變更: 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 版的變更: 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 版的變更: 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()

  回傳一個 `time.struct_time`，如同 `time.localtime()` 所回傳。

  `d.timetuple()` 等價於：

      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.

  警告

  Because naive `datetime` objects are treated by many `datetime` methods as local times, it is preferred to use aware datetimes to represent times in UTC; as a result, using `datetime.utctimetuple()` may give misleading results. If you have a naive `datetime` representing UTC, use `datetime.replace(tzinfo=timezone.utc)` to make it aware, at which point you can use `datetime.timetuple()`.

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 platform C functions to perform the conversion. Since `datetime` supports a wider range of values than the platform C functions on many platforms, this method may raise `OverflowError` or `OSError` 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()

  備註

  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 time zone 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)

  在 3.3 版被加入.

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

  在 3.6 版的變更: This method no longer relies on the platform C `mktime()` function to perform conversions.

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 named tuple with three components: `year`, `week` and `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`，如果 `microsecond` 不是 0

  - `YYYY-MM-DDTHH:MM:SS`，如果 `microsecond` 是 0

  如果 `utcoffset()` 没有回傳 `None`，則會附加一个字串，給出 UTC 偏移：

  - `YYYY-MM-DDTHH:MM:SS.ffffff+HH:MM[:SS[.ffffff]]`，如果 `microsecond` 不是 0

  - `YYYY-MM-DDTHH:MM:SS+HH:MM[:SS[.ffffff]]`，如果 `microsecond` 是 0

  範例：

      >>> import datetime as dt
      >>> dt.datetime(2019, 5, 18, 15, 17, 8, 132263).isoformat()
      '2019-05-18T15:17:08.132263'
      >>> dt.datetime(2019, 5, 18, 15, 17, tzinfo=dt.timezone.utc).isoformat()
      '2019-05-18T15:17:00+00:00'

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

      >>> import datetime as dt
      >>> class TZ(dt.tzinfo):
      ...     """A time zone with an arbitrary, constant -06:39 offset."""
      ...     def utcoffset(self, when):
      ...         return dt.timedelta(hours=-6, minutes=-39)
      ...
      >>> dt.datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
      '2002-12-25 00:00:00-06:39'
      >>> dt.datetime(2009, 11, 27, microsecond=100, tzinfo=TZ()).isoformat()
      '2009-11-27T00:00:00.000100-06:39'

  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.

  備註

  Excluded time components are truncated, not rounded.

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

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

  在 3.6 版的變更: 新增 timespec 參數。

datetime.__str__()

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

datetime.ctime()

  Return a string representing the date and time:

      >>> import datetime as dt
      >>> dt.datetime(2002, 12, 4, 20, 30, 40).ctime()
      'Wed Dec  4 20:30:40 2002'

  The output string will not include time zone information, regardless of whether the input is aware or naive.

  `d.ctime()` 等價於：

      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. See also strftime() 與 strptime() 的行為 and `datetime.isoformat()`.

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()`. See also strftime() 與 strptime() 的行為 and `datetime.isoformat()`.

### 用法範例：`datetime`

更多 `datetime` 的用法範例：

    >>> import datetime as dt

    >>> # Using datetime.combine()
    >>> d = dt.date(2005, 7, 14)
    >>> t = dt.time(12, 30)
    >>> dt.datetime.combine(d, t)
    datetime.datetime(2005, 7, 14, 12, 30)

    >>> # Using datetime.now()
    >>> dt.datetime.now()
    datetime.datetime(2007, 12, 6, 16, 29, 43, 79043)   # GMT +1
    >>> dt.datetime.now(dt.timezone.utc)
    datetime.datetime(2007, 12, 6, 15, 29, 43, 79060, tzinfo=datetime.timezone.utc)

    >>> # Using datetime.strptime()
    >>> my_datetime = dt.datetime.strptime("21/11/06 16:30", "%d/%m/%y %H:%M")
    >>> my_datetime
    datetime.datetime(2006, 11, 21, 16, 30)

    >>> # Using datetime.timetuple() to get tuple of all attributes
    >>> tt = my_datetime.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 = my_datetime.isocalendar()
    >>> for it in ic:
    ...     print(it)
    ...
    2006    # ISO year
    47      # ISO week
    2       # ISO weekday

    >>> # Formatting a datetime
    >>> my_datetime.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(my_datetime, "day", "month", "time")
    'The day is 21, the month is November, the time is 04:30PM.'

The example below defines a `tzinfo` subclass capturing time zone information for Kabul, Afghanistan, which used +4 UTC until 1945 and then +4:30 UTC thereafter:

    import datetime as dt

    class KabulTz(dt.tzinfo):
        # Kabul used +4 until 1945, when they moved to +4:30
        UTC_MOVE_DATE = dt.datetime(1944, 12, 31, 20, tzinfo=dt.timezone.utc)

        def utcoffset(self, when):
            if when.year < 1945:
                return dt.timedelta(hours=4)
            elif (1945, 1, 1, 0, 0) <= when.timetuple()[:5] < (1945, 1, 1, 0, 30):
                # An ambiguous ("imaginary") half-hour range representing
                # a 'fold' in time due to the shift from +4 to +4:30.
                # If when falls in the imaginary range, use fold to decide how
                # to resolve. See PEP 495.
                return dt.timedelta(hours=4, minutes=(30 if when.fold else 0))
            else:
                return dt.timedelta(hours=4, minutes=30)

        def fromutc(self, when):
            # Follow same validations as in datetime.tzinfo
            if not isinstance(when, dt.datetime):
                raise TypeError("fromutc() requires a datetime argument")
            if when.tzinfo is not self:
                raise ValueError("when.tzinfo is not self")

            # 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.
            if when.replace(tzinfo=dt.timezone.utc) >= self.UTC_MOVE_DATE:
                return when + dt.timedelta(hours=4, minutes=30)
            else:
                return when + dt.timedelta(hours=4)

        def dst(self, when):
            # Kabul does not observe daylight saving time.
            return dt.timedelta(0)

        def tzname(self, when):
            if when >= self.UTC_MOVE_DATE:
                return "+04:30"
            return "+04"

Usage of `KabulTz` from above:

    >>> tz1 = KabulTz()

    >>> # Datetime before the change
    >>> dt1 = dt.datetime(1900, 11, 21, 16, 30, tzinfo=tz1)
    >>> print(dt1.utcoffset())
    4:00:00

    >>> # Datetime after the change
    >>> dt2 = dt.datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
    >>> print(dt2.utcoffset())
    4:30:00

    >>> # Convert datetime to another time zone
    >>> dt3 = dt2.astimezone(dt.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 == dt3
    True

## `time` 物件

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 must 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`.

類別屬性：

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.

Instance attributes (read-only):

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 values 0 and 1 represent, respectively, the earlier and later of the two moments with the same wall time representation.

  在 3.6 版被加入.

`time` objects support equality and order comparisons, where `a` is considered less than `b` when `a` precedes `b` in time.

Naive and aware `time` objects are never equal. Order comparison between naive and aware `time` objects raises `TypeError`.

If both comparands are aware, and have the same `tzinfo` attribute, the `tzinfo` and `fold` attributes are 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()`).

在 3.3 版的變更: Equality comparisons between aware and naive `time` instances don't raise `TypeError`.

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

在 3.5 版的變更: 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 more information.

其他建構函式：

classmethod time.fromisoformat(time_string)

  Return a `time` corresponding to a time_string in any valid ISO 8601 format, with the following exceptions:

  1. Time zone offsets may have fractional seconds.

  2. The leading `T`, normally required in cases where there may be ambiguity between a date and a time, is not required.

  3. Fractional seconds may have any number of digits (anything beyond 6 will be truncated).

  4. Fractional hours and minutes are not supported.

  範例：

      >>> import datetime as dt
      >>> dt.time.fromisoformat('04:23:01')
      datetime.time(4, 23, 1)
      >>> dt.time.fromisoformat('T04:23:01')
      datetime.time(4, 23, 1)
      >>> dt.time.fromisoformat('T042301')
      datetime.time(4, 23, 1)
      >>> dt.time.fromisoformat('04:23:01.000384')
      datetime.time(4, 23, 1, 384)
      >>> dt.time.fromisoformat('04:23:01,000384')
      datetime.time(4, 23, 1, 384)
      >>> dt.time.fromisoformat('04:23:01+04:00')
      datetime.time(4, 23, 1, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))
      >>> dt.time.fromisoformat('04:23:01Z')
      datetime.time(4, 23, 1, tzinfo=datetime.timezone.utc)
      >>> dt.time.fromisoformat('04:23:01+00:00')
      datetime.time(4, 23, 1, tzinfo=datetime.timezone.utc)

  在 3.7 版被加入.

  在 3.11 版的變更: Previously, this method only supported formats that could be emitted by `time.isoformat()`.

classmethod time.strptime(date_string, format)

  Return a `time` corresponding to date_string, parsed according to format.

  If format does not contain microseconds or timezone information, this is equivalent to:

      time(*(time.strptime(date_string, format)[3:6]))

  `ValueError` is raised if the date_string and format cannot be parsed by `time.strptime()` or if it returns a value which is not a time tuple. See also strftime() 與 strptime() 的行為 and `time.fromisoformat()`.

  在 3.14 版被加入.

實例方法：

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

  Return a new `time` with the same values, but with specified parameters updated. Note that `tzinfo=None` can be specified to create a naive `time` from an aware `time`, without conversion of the time data.

  `time` objects are also supported by generic function `copy.replace()`.

  在 3.6 版的變更: 新增 fold 參數。

time.isoformat(timespec='auto')

  Return a string representing the time in ISO 8601 format, one of:

  - `HH:MM:SS.ffffff`, if `microsecond` is not 0

  - `HH:MM:SS`, if `microsecond` is 0

  - `HH:MM:SS.ffffff+HH:MM[:SS[.ffffff]]`, if `utcoffset()` does not return `None`

  - `HH:MM:SS+HH:MM[:SS[.ffffff]]`, if `microsecond` is 0 and `utcoffset()` does not return `None`

  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.

  備註

  Excluded time components are truncated, not rounded.

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

  範例：

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

  在 3.6 版的變更: 新增 timespec 參數。

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. See also strftime() 與 strptime() 的行為 and `time.isoformat()`.

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()`. See also strftime() 與 strptime() 的行為 and `time.isoformat()`.

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 版的變更: 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 版的變更: 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.

### 用法範例：`time`

Examples of working with a `time` object:

    >>> import datetime as dt
    >>> class TZ1(dt.tzinfo):
    ...     def utcoffset(self, when):
    ...         return dt.timedelta(hours=1)
    ...     def dst(self, when):
    ...         return dt.timedelta(0)
    ...     def tzname(self, when):
    ...         return "+01:00"
    ...     def  __repr__(self):
    ...         return f"{self.__class__.__name__}()"
    ...
    >>> t = dt.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` 物件

class datetime.tzinfo

  This is an abstract base class, meaning that this class should not be instantiated directly. Define a subclass of `tzinfo` to capture information about a particular time zone.

  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.

  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 provides `timezone`, a simple concrete subclass of `tzinfo` which can represent time zones with fixed offset from UTC such as UTC itself or North American EST and EDT.

  Special requirement for pickling: A `tzinfo` subclass must have an `__init__()` method that can be called with no arguments, otherwise 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.

  This represents 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 版的變更: 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:

      import datetime as dt

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

  或是：

      import datetime as dt

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

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

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

  在 3.7 版的變更: 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 time zones.

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:

      import datetime as dt

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

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

    import datetime as dt

    # 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

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

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

    DSTDIFF = DSTOFFSET - STDOFFSET

    class LocalTimezone(dt.tzinfo):

        def fromutc(self, when):
            assert when.tzinfo is self
            stamp = (when - 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 dt.datetime(*args, microsecond=when.microsecond,
                               tzinfo=self, fold=fold)

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

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

        def tzname(self, when):
            return time.tzname[self._isdst(when)]

        def _isdst(self, when):
            tt = (when.year, when.month, when.day,
                  when.hour, when.minute, when.second,
                  when.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(when):
        days_to_go = 6 - when.weekday()
        if days_to_go:
            when += dt.timedelta(days_to_go)
        return when

    # 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
    # https://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 = dt.datetime(1, 3, 8, 2)
    # and ends at 2am (DST time) on the first Sunday of Nov.
    DSTEND_2007 = dt.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 = dt.datetime(1, 4, 1, 2)
    DSTEND_1987_2006 = dt.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 = dt.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 (dt.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(dt.tzinfo):

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

        def __repr__(self):
            return self.reprname

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

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

        def dst(self, when):
            if when is None or when.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 when.tzinfo is self.
                return ZERO
            assert when.tzinfo is self
            start, end = us_dst_range(when.year)
            # Can't compare naive to aware objects, so strip the timezone from
            # when first.
            when = when.replace(tzinfo=None)
            if start + HOUR <= when < end - HOUR:
                # DST is in effect.
                return HOUR
            if end - HOUR <= when < end:
                # Fold (an ambiguous hour): use when.fold to disambiguate.
                return ZERO if when.fold else HOUR
            if start <= when < start + HOUR:
                # Gap (a non-existent hour): reverse the fold rule.
                return HOUR if when.fold else ZERO
            # DST is off.
            return ZERO

        def fromutc(self, when):
            assert when.tzinfo is self
            start, end = us_dst_range(when.year)
            start = start.replace(tzinfo=self)
            end = end.replace(tzinfo=self)
            std_time = when + 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:

    >>> import datetime as dt
    >>> from tzinfo_examples import HOUR, Eastern
    >>> u0 = dt.datetime(2016, 3, 13, 5, tzinfo=dt.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:

    >>> import datetime as dt
    >>> from tzinfo_examples import HOUR, Eastern
    >>> u0 = dt.datetime(2016, 11, 6, 4, tzinfo=dt.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)).

也參考

> `zoneinfo`

>   The `datetime` module has a basic `timezone` class (for handling arbitrary fixed offsets from UTC) and its `timezone.utc` attribute (a UTC `timezone` instance).

>   `zoneinfo` brings the IANA time zone database (also known as the Olson database) to Python, and its usage is recommended.

IANA 時區資料庫

  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` 物件

The `timezone` class is a subclass of `tzinfo`, each instance of which represents a time zone defined by a fixed offset from UTC.

Objects of this class cannot be used to represent time zone 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])

  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.

  在 3.2 版被加入.

  在 3.7 版的變更: 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 版的變更: 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 in the format `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 版的變更: Name generated from `offset=timedelta(0)` is now plain `'UTC'`, not `'UTC+00:00'`.

timezone.dst(dt)

  總是回傳 `None`。

timezone.fromutc(dt)

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

類別屬性：

timezone.utc

  UTC 時區，`timezone(timedelta(0))`。

## `strftime()` 與 `strptime()` 的行為

`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.

Conversely, the `date.strptime()`, `datetime.strptime()` and `time.strptime()` class methods create an object from a string representing the time and a corresponding format string.

The table below provides a high-level comparison of `strftime()` versus `strptime()`:

| `strftime` | `strptime`
--- | --- | ---
用法 | Convert object to a string according to a given format | Parse a string into an object given a corresponding format
Type of method | 實例方法 | 類別方法
Signature | `strftime(format)` | `strptime(date_string, format)`

### `strftime()` 與 `strptime()` 格式碼

These methods accept format codes that can be used to parse and format dates:

    >>> import datetime as dt
    >>> dt.datetime.strptime('31/01/22 23:59:59.999999',
    ...                      '%d/%m/%y %H:%M:%S.%f')
    datetime.datetime(2022, 1, 31, 23, 59, 59, 999999)
    >>> _.strftime('%a %d %b %Y, %I:%M%p')
    'Mon 31 Jan 2022, 11:59PM'

The following is a list of all the format codes that the 2011 C standard requires, and these work on all supported platforms.

Directive | 含義 | 範例 | 註解
--- | --- | --- | ---
`%a` | Weekday as locale's abbreviated name. | Sun, Mon, ..., Sat (en_US); So, Mo, ..., Sa (de_DE) | (1)
`%A` | Weekday as locale's full name. | Sunday, Monday, ..., Saturday (en_US); Sonntag, Montag, ..., Samstag (de_DE) | (1)
`%b` | Month as locale's abbreviated name. | Jan, Feb, ..., Dec (en_US); Jan, Feb, ..., Dez (de_DE) | (1)
`%B` | Month as locale's full name. | January, February, ..., December (en_US); Januar, Februar, ..., Dezember (de_DE) | (1)
`%c` | Locale's appropriate date and time representation. | Tue Aug 16 21:30:00 1988 (en_US); Di 16 Aug 21:30:00 1988 (de_DE) | (1)
`%C` | The year divided by 100 and truncated to an integer as a zero-padded decimal number. | 01, 02, ..., 99 | (0)
`%d` | Day of the month as a zero-padded decimal number. | 01, 02, ..., 31 | (9), (10)
`%D` | Equivalent to `%m/%d/%y`. | 11/28/25 | (9)
`%e` | The day of the month as a space-padded decimal number. | ␣1, ␣2, ..., 31 | (10)
`%F` | Equivalent to `%Y-%m-%d`, the ISO 8601 format. | 2025-10-11, 1001-12-30 |
`%g` | Last 2 digits of ISO 8601 year representing the year that contains the greater part of the ISO week (`%V`). | 00, 01, ..., 99 | (0)
`%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)
`%h` | Equivalent to `%b`. | See `%b`. | (0)
`%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)
`%j` | Day of the year as a zero-padded decimal number. | 001, 002, ..., 366 | (9)
`%m` | 以零填充的並以十進位數字表示的月份。 | 01, 02, ..., 12 | (9)
`%M` | Minute as a zero-padded decimal number. | 00, 01, ..., 59 | (9)
`%n` | The newline character (`'\n'`). For `strptime()`, zero or more whitespace. | `\n` |
`%p` | Locale's equivalent of either AM or PM. | AM, PM (en_US); am, pm (de_DE) | (1), (3)
`%r` | Locale's 12-hour clock time. | 12:00:00 AM | (1), (0)
`%R` | Equivalent to `%H:%M`. | 10:01 |
`%S` | Second as a zero-padded decimal number. | 00, 01, ..., 59 | (4), (9)
`%t` | The tab character (`'\t'`). For `strptime()`, zero or more whitespace. | `\t` |
`%T` | ISO 8601 time format, equivalent to `%H:%M:%S`. | 10:01:59 |
`%u` | ISO 8601 weekday as a decimal number where 1 is Monday. | 1, 2, ..., 7 |
`%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)
`%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)
`%w` | Weekday as a decimal number, where 0 is Sunday and 6 is Saturday. | 0, 1, ..., 6 |
`%W` | Week number of the year (Monday as the first day of the week) as a zero-padded decimal number. All days in a new year preceding the first Monday are considered to be in week 0. | 00, 01, ..., 53 | (7), (9)
`%x` | Locale's appropriate date representation. | 08/16/88 (None); 08/16/1988 (en_US); 16.08.1988 (de_DE) | (1)
`%X` | Locale's appropriate time representation. | 21:30:00 (en_US); 21:30:00 (de_DE) | (1)
`%y` | Year without century as a zero-padded decimal number. | 00, 01, ..., 99 | (9)
`%Y` | Year with century as a decimal number. | 0001, 0002, ..., 2013, 2014, ..., 9998, 9999 | (2)
`%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, GMT | (6)
`%%` | A literal `'%'` character. | % |

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`.

Several additional directives not required by the C11 standard are included for convenience.

Directive | 含義 | 範例 | 註解
--- | --- | --- | ---
`%f` | Microsecond as a decimal number, zero-padded to 6 digits. | 000000, 000001, ..., 999999 | (5)
`%:z` | UTC offset in the form `±HH:MM[:SS[.ffffff]]` (empty string if the object is naive). | (empty), +00:00, -04:00, +10:30, +06:34:15, -03:07:12.345216 | (6)

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. There are also differences between platforms in handling of unsupported format specifiers.

在 3.6 版被加入: 新增 `%G`、`%u` 與 `%V`。

在 3.12 版被加入: `%:z` was added for `strftime()`.

在 3.15 版被加入: `%D`, `%F`, `%n`, `%t`, and `%:z` were added for `strptime()`.

### 技術細節

Broadly speaking, `d.strftime(fmt)` acts like the `time` module's `time.strftime(fmt, d.timetuple())` although not all objects support a `timetuple()` method.

For the `datetime.strptime()` and `date.strptime()` class methods, 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.

備註

Format strings without separators can be ambiguous for parsing. For example, with `%Y%m%d`, the string `2026111` may be parsed either as `2026-11-01` or as `2026-01-11`. Use separators to ensure the input is parsed as intended.

備註

When used to parse partial dates lacking a year, `datetime.strptime()` and `date.strptime()` will raise when encountering February 29 because the default year of 1900 is not a leap year. Always add a default leap year to partial date strings before parsing.

    >>> import datetime as dt
    >>> value = "2/29"
    >>> dt.datetime.strptime(value, "%m/%d")
    Traceback (most recent call last):
    ...
    ValueError: day 29 must be in range 1..28 for month 2 in year 1900
    >>> dt.datetime.strptime(f"1904 {value}", "%Y %m/%d")
    datetime.datetime(1904, 2, 29, 0, 0)

Using `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 time zone offset information, which are supported in `datetime.strptime` but are discarded by `time.strptime`.

對 `time` 物件來說，不應該使用年、月、日的格式碼，因為 `time` 物件並沒有這些值。如果使用這些格式碼，年份會以 1900 代替、月及日會以 1 代替。

對 `date` 物件來說，不應該使用時、分、秒、微秒的格式碼，因為 `date` 物件並沒有這些值。如果使用這些格式碼，這些值都會以 0 代替。

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.

註解：

0. This format code is currently unsupported by `strptime()`.

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 non-ASCII characters.

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 版的變更: In previous versions, `strftime()` method was restricted to years >= 1900.

   在 3.3 版的變更: In version 3.2, `strftime()` method was restricted to 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. Unlike the `time` module, the `datetime` module does not support leap seconds.

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`, `%:z` and `%Z` format codes are replaced by empty strings.

   For an aware object:

   `%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 版的變更: The UTC offset is not restricted to a whole number of minutes.

   在 3.7 版的變更: 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, both `'+010000'` and `'+01:00:00'` will be parsed as an offset of one hour. In addition, providing `'Z'` is identical to `'+00:00'`.

   `%:z`

     When used with `strftime()`, behaves exactly as `%z`, except that a colon separator is added between hours, minutes and seconds.

     When used with `strptime()`, the UTC offset is required to have a colon as a separator between hours, minutes and seconds. For example, `'+01:00:00'` (but not `'+010000'`) will be parsed as an offset of one hour. In addition, providing `'Z'` is identical to `'+00:00'`.

   `%Z`

     In `strftime()`, `%Z` is replaced by an empty string if `tzname()` returns `None`; otherwise `%Z` is replaced by the returned value, which must be a string.

     `strptime()` only accepts certain values for `%Z`:

     1. any value in `time.tzname` for your machine's locale

     2. the hard-coded values `UTC` and `GMT`

     So someone living in Japan may have `JST`, `UTC`, and `GMT` as valid values, but probably not `EST`. It will raise `ValueError` for invalid values.

   在 3.2 版的變更: 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.

10. When parsing a month and day using `strptime()`, always include a year in the format. If the value you need to parse lacks a year, append an explicit dummy leap year. Otherwise your code will raise an exception when it encounters leap day because the default year used by the parser (1900) is not a leap year. Users run into that bug every leap year.

        >>> month_day = "02/29"
        >>> dt.datetime.strptime(f"{month_day};1984", "%m/%d;%Y")  # 沒有閏年問題。
        datetime.datetime(1984, 2, 29, 0, 0)

    在 3.15 版的變更: Using `%d` without a year now raises `ValueError`.

    自從版本 3.15 後不推薦使用，將會自版本 3.17 中移除。: `strptime()` calls using a format string containing `%e` without a year now emit a `DeprecationWarning`.

註解

[1]

也就是說，我們會忽略相對論的效應。

[2]

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.

[3]

See R. H. van Gent's guide to the mathematics of the ISO 8601 calendar for a good explanation.