"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.

  Package dateutil
     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 e.g.
     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:

   object
       timedelta
       tzinfo
           timezone
       time
       date
           datetime


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"

Otherwise, "d" is naive.

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"。

Otherwise, "t" is naive.

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:

      >>> from datetime import timedelta
      >>> delta = 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)

   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:

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

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:

        >>> from datetime import timedelta
        >>> duration = 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 //    | The floor is computed and the remainder (if     |
| t3"                              | 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"                            | Equivalent to "timedelta(-t1.days, -t1.seconds, |
|                                  | -t1.microseconds)", and to "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 (e.g. "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
   >>> from datetime import timedelta
   >>> year = timedelta(days=365)
   >>> another_year = timedelta(weeks=40, days=84, hours=23,
   ...                          minutes=50, seconds=600)
   >>> year == another_year
   True
   >>> year.total_seconds()
   31536000.0

Examples of "timedelta" arithmetic:

   >>> from datetime import timedelta
   >>> year = 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 <= number of days in the given month and year"

   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.

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：

      >>> from datetime import date
      >>> date.fromisoformat('2019-12-04')
      datetime.date(2019, 12, 4)
      >>> date.fromisoformat('20191204')
      datetime.date(2019, 12, 4)
      >>> 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.

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 !=      | Equality comparison. (4)                       |
| date2"                          |                                                |
+---------------------------------+------------------------------------------------+
| "date1 < date2" "date1 > date2" | Order comparison. (5)                          |
| "date1 <= date2" "date1 >=      |                                                |
| date2"                          |                                                |
+---------------------------------+------------------------------------------------+

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.

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()".

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：

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

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:

      >>> from datetime import date
      >>> date(2003, 12, 29).isocalendar()
      datetime.IsoCalendarDate(year=2004, week=1, weekday=1)
      >>> 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：

      >>> from datetime import date
      >>> 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:

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

更多 "date" 的用法範例：

   >>> from datetime import date
   >>> d = 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 to 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.

Constructor:

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.

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 3.12 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：

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

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 !=  | Equality comparison. (4)         |
| datetime2"                              |                                  |
+-----------------------------------------+----------------------------------+
| "datetime1 < datetime2" "datetime1 >    | Order comparison. (5)            |
| datetime2" "datetime1 <= datetime2"     |                                  |
| "datetime1 >= datetime2"                |                                  |
+-----------------------------------------+----------------------------------+

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

   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, as
   well as a "datetime" object and a "date" object that is not also a
   "datetime" instance, 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".

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.

   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 the platform C "mktime()" function to perform
   the conversion. Since "datetime" supports wider range of values
   than "mktime()" on many platforms, this method may raise
   "OverflowError" 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()

   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.

   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)

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：

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

      >>> from datetime import tzinfo, timedelta, datetime
      >>> class TZ(tzinfo):
      ...     """A time zone with an arbitrary, constant -06:39 offset."""
      ...     def utcoffset(self, dt):
      ...         return timedelta(hours=-6, minutes=-39)
      ...
      >>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
      '2002-12-25 00:00:00-06:39'
      >>> 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:

      >>> from datetime import datetime
      >>> datetime.now().isoformat(timespec='minutes')
      '2002-12-25T00:00'
      >>> dt = datetime(2015, 1, 1, 12, 30, 59, 0)
      >>> dt.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:

      >>> from datetime import datetime
      >>> 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：

   >>> from datetime import datetime, date, time, timezone

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

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

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

   >>> # Using datetime.timetuple() to get tuple of all attributes
   >>> tt = dt.timetuple()
   >>> for it in tt:
   ...     print(it)
   ...
   2006    # year
   11      # month
   21      # day
   16      # hour
   30      # minute
   0       # second
   1       # weekday (0 = Monday)
   325     # number of days since 1st January
   -1      # dst - method tzinfo.dst() returned None

   >>> # Date in ISO format
   >>> ic = dt.isocalendar()
   >>> for it in ic:
   ...     print(it)
   ...
   2006    # ISO year
   47      # ISO week
   2       # ISO weekday

   >>> # Formatting a datetime
   >>> dt.strftime("%A, %d. %B %Y %I:%M%p")
   'Tuesday, 21. November 2006 04:30PM'
   >>> 'The {1} is {0:%d}, the {2} is {0:%B}, the {3} is {0:%I:%M%p}.'.format(dt, "day", "month", "time")
   'The day is 21, the month is November, the time is 04:30PM.'

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:

   from datetime import timedelta, datetime, tzinfo, timezone

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

       def utcoffset(self, dt):
           if dt.year < 1945:
               return timedelta(hours=4)
           elif (1945, 1, 1, 0, 0) <= dt.timetuple()[:5] < (1945, 1, 1, 0, 30):
               # An ambiguous ("imaginary") half-hour range representing
               # a 'fold' in time due to the shift from +4 to +4:30.
               # If dt falls in the imaginary range, use fold to decide how
               # to resolve. See PEP495.
               return timedelta(hours=4, minutes=(30 if dt.fold else 0))
           else:
               return timedelta(hours=4, minutes=30)

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

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

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

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

Usage of "KabulTz" from above:

   >>> tz1 = KabulTz()

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

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

   >>> # Convert datetime to another time zone
   >>> dt3 = dt2.astimezone(timezone.utc)
   >>> dt3
   datetime.datetime(2006, 6, 14, 8, 30, tzinfo=datetime.timezone.utc)
   >>> dt2
   datetime.datetime(2006, 6, 14, 13, 0, tzinfo=KabulTz())
   >>> dt2 == 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 full details.

Other constructor:

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：

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

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.

   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：

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

   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:

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


"tzinfo" 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:

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

   或是：

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

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

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

   在 3.7 版的變更: 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:

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

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

   from datetime import tzinfo, timedelta, datetime

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

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

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

   DSTDIFF = DSTOFFSET - STDOFFSET

   class LocalTimezone(tzinfo):

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

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

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

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

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

   Local = LocalTimezone()


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

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


   # US DST Rules
   #
   # This is a simplified (i.e., wrong for a few cases) set of rules for US
   # DST start and end times. For a complete and up-to-date set of DST rules
   # and timezone definitions, visit the Olson Database (or try pytz):
   # http://www.twinsun.com/tz/tz-link.htm
   # 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 = datetime(1, 3, 8, 2)
   # and ends at 2am (DST time) on the first Sunday of Nov.
   DSTEND_2007 = datetime(1, 11, 1, 2)
   # From 1987 to 2006, DST used to start at 2am (standard time) on the first
   # Sunday in April and to end at 2am (DST time) on the last
   # Sunday of October, which is the first Sunday on or after Oct 25.
   DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
   DSTEND_1987_2006 = datetime(1, 10, 25, 2)
   # From 1967 to 1986, DST used to start at 2am (standard time) on the last
   # Sunday in April (the one on or after April 24) and to end at 2am (DST time)
   # on the last Sunday of October, which is the first Sunday
   # on or after Oct 25.
   DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
   DSTEND_1967_1986 = DSTEND_1987_2006

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

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


   class USTimeZone(tzinfo):

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

       def __repr__(self):
           return self.reprname

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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=None)

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

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

   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 "datetime.strptime()" class method creates a
"datetime" object from a string representing a date and 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 a "datetime" object given a corresponding format           |
+------------------+----------------------------------------------------------+--------------------------------------------------------------------------------+
| Type of method   | 實例方法                                                 | 類別方法                                                                       |
+------------------+----------------------------------------------------------+--------------------------------------------------------------------------------+
| Method of        | "date"; "datetime"; "time"                               | "datetime"                                                                     |
+------------------+----------------------------------------------------------+--------------------------------------------------------------------------------+
| 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:

   >>> 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 1989 C
standard requires, and these work on all platforms with a standard C
implementation.

+-------------+----------------------------------+--------------------------+---------+
| Directive   | 含義                             | 範例                     | 註解    |
|=============|==================================|==========================|=========|
| "%a"        | Weekday as locale's abbreviated  | Sun, Mon, ..., Sat       | (1)     |
|             | name.                            | (en_US); So, Mo, ..., Sa |         |
|             |                                  | (de_DE)                  |         |
+-------------+----------------------------------+--------------------------+---------+
| "%A"        | Weekday as locale's full name.   | Sunday, Monday, ...,     | (1)     |
|             |                                  | Saturday (en_US);        |         |
|             |                                  | Sonntag, Montag, ...,    |         |
|             |                                  | Samstag (de_DE)          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%w"        | Weekday as a decimal number,     | 0, 1, ..., 6             |         |
|             | where 0 is Sunday and 6 is       |                          |         |
|             | Saturday.                        |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%d"        | Day of the month as a zero-      | 01, 02, ..., 31          | (9)     |
|             | padded decimal number.           |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%b"        | Month as locale's abbreviated    | Jan, Feb, ..., Dec       | (1)     |
|             | name.                            | (en_US); Jan, Feb, ...,  |         |
|             |                                  | Dez (de_DE)              |         |
+-------------+----------------------------------+--------------------------+---------+
| "%B"        | Month as locale's full name.     | January, February, ...,  | (1)     |
|             |                                  | December (en_US);        |         |
|             |                                  | Januar, Februar, ...,    |         |
|             |                                  | Dezember (de_DE)         |         |
+-------------+----------------------------------+--------------------------+---------+
| "%m"        | 以零填充的並以十進位數字表示的月 | 01, 02, ..., 12          | (9)     |
|             | 份。                             |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%y"        | Year without century as a zero-  | 00, 01, ..., 99          | (9)     |
|             | padded decimal number.           |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%Y"        | Year with century as a decimal   | 0001, 0002, ..., 2013,   | (2)     |
|             | number.                          | 2014, ..., 9998, 9999    |         |
+-------------+----------------------------------+--------------------------+---------+
| "%H"        | Hour (24-hour clock) as a zero-  | 00, 01, ..., 23          | (9)     |
|             | padded decimal number.           |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%I"        | Hour (12-hour clock) as a zero-  | 01, 02, ..., 12          | (9)     |
|             | padded decimal number.           |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%p"        | Locale's equivalent of either AM | AM, PM (en_US); am, pm   | (1),    |
|             | or PM.                           | (de_DE)                  | (3)     |
+-------------+----------------------------------+--------------------------+---------+
| "%M"        | Minute as a zero-padded decimal  | 00, 01, ..., 59          | (9)     |
|             | number.                          |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%S"        | Second as a zero-padded decimal  | 00, 01, ..., 59          | (4),    |
|             | number.                          |                          | (9)     |
+-------------+----------------------------------+--------------------------+---------+
| "%f"        | Microsecond as a decimal number, | 000000, 000001, ...,     | (5)     |
|             | zero-padded to 6 digits.         | 999999                   |         |
+-------------+----------------------------------+--------------------------+---------+
| "%z"        | UTC offset in the form           | (empty), +0000, -0400,   | (6)     |
|             | "±HHMM[SS[.ffffff]]" (empty      | +1030, +063415,          |         |
|             | string if the object is naive).  | -030712.345216           |         |
+-------------+----------------------------------+--------------------------+---------+
| "%Z"        | Time zone name (empty string if  | (empty), UTC, GMT        | (6)     |
|             | the object is naive).            |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%j"        | Day of the year as a zero-padded | 001, 002, ..., 366       | (9)     |
|             | decimal number.                  |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%U"        | Week number of the year (Sunday  | 00, 01, ..., 53          | (7),    |
|             | as the first day of the week) as |                          | (9)     |
|             | a zero-padded decimal number.    |                          |         |
|             | All days in a new year preceding |                          |         |
|             | the first Sunday are considered  |                          |         |
|             | to be in week 0.                 |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%W"        | Week number of the year (Monday  | 00, 01, ..., 53          | (7),    |
|             | as the first day of the week) as |                          | (9)     |
|             | a zero-padded decimal number.    |                          |         |
|             | All days in a new year preceding |                          |         |
|             | the first Monday are considered  |                          |         |
|             | to be in week 0.                 |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%c"        | Locale's appropriate date and    | Tue Aug 16 21:30:00 1988 | (1)     |
|             | time representation.             | (en_US); Di 16 Aug       |         |
|             |                                  | 21:30:00 1988 (de_DE)    |         |
+-------------+----------------------------------+--------------------------+---------+
| "%x"        | Locale's appropriate date        | 08/16/88 (None);         | (1)     |
|             | representation.                  | 08/16/1988 (en_US);      |         |
|             |                                  | 16.08.1988 (de_DE)       |         |
+-------------+----------------------------------+--------------------------+---------+
| "%X"        | Locale's appropriate time        | 21:30:00 (en_US);        | (1)     |
|             | representation.                  | 21:30:00 (de_DE)         |         |
+-------------+----------------------------------+--------------------------+---------+
| "%%"        | A literal "'%'" character.       | %                        |         |
+-------------+----------------------------------+--------------------------+---------+

Several additional directives not required by the C89 standard are
included for convenience. These parameters all correspond to ISO 8601
date values.

+-------------+----------------------------------+--------------------------+---------+
| Directive   | 含義                             | 範例                     | 註解    |
|=============|==================================|==========================|=========|
| "%G"        | ISO 8601 year with century       | 0001, 0002, ..., 2013,   | (8)     |
|             | representing the year that       | 2014, ..., 9998, 9999    |         |
|             | contains the greater part of the |                          |         |
|             | ISO week ("%V").                 |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%u"        | ISO 8601 weekday as a decimal    | 1, 2, ..., 7             |         |
|             | number where 1 is Monday.        |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%V"        | ISO 8601 week as a decimal       | 01, 02, ..., 53          | (8),    |
|             | number with Monday as the first  |                          | (9)     |
|             | day of the week. Week 01 is the  |                          |         |
|             | week containing Jan 4.           |                          |         |
+-------------+----------------------------------+--------------------------+---------+
| "%:z"       | UTC offset in the form           | (empty), +00:00, -04:00, | (6)     |
|             | "±HH:MM[:SS[.ffffff]]" (empty    | +10:30, +06:34:15,       |         |
|             | string if the object is naive).  | -03:07:12.345216         |         |
+-------------+----------------------------------+--------------------------+---------+

These may not be available on all platforms when used with the
"strftime()" method. The ISO 8601 year and ISO 8601 week directives
are not interchangeable with the year and week number directives
above. Calling "strptime()" with incomplete or ambiguous ISO 8601
directives will raise a "ValueError".

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: 新增 "%:z"。


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

備註:

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

   >>> from datetime import datetime
   >>> value = "2/29"
   >>> datetime.strptime(value, "%m/%d")
   Traceback (most recent call last):
   ...
   ValueError: day is out of range for month
   >>> 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：

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,
   "'+01:00:00'" will be parsed as an offset of one hour. In addition,
   providing "'Z'" is identical to "'+00:00'".

   "%:z"
      Behaves exactly as "%z", but has a colon separator added between
      hours, minutes and seconds.

   "%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. Parsing dates without a year using "strptime()" will fail on
    representations of February 29 as that date does not exist in the
    default year of 1900.

-[ 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.
