"time" --- 時間存取與轉換
*************************

======================================================================

這個模組提供了各種與時間相關的函式。若要查看相關功能，請參閱
"datetime" 和 "calendar" 模組。

雖然這個模組隨時可用，但並非所有函式在所有平台上都可用。這個模組中定義
的大多數函式都會呼叫 C 語言平台的函式庫中具有相同名稱的函式。由於這些
函式的語義因平台而異，所以偶爾查閱平台文件可能會有所幫助。

以下是對一些術語和慣例的說明。

* *epoch* 是起始的時間點，即 "time.gmtime(0)" 的回傳值。在所有平台上，
  它是 1970 年 1 月 1 日，00:00:00（UTC）。

* 術語 *seconds since the epoch（紀元秒數）* 是指從 epoch（紀元）開始
  經過的總秒數，通常不包括 leap seconds。在所有符合 POSIX 標準的平台上
  ，leap seconds （閏秒）都不計入這個總數。

* 這個模組中的函式可能無法處理 epoch 之前或遙遠未來的日期和時間。未來
  的臨界點由 C 函式庫決定；對於 32 位元系統來說通常是在 2038 年。

* 函式 "strptime()" 在給定 "%y" 格式程式碼時可以解析兩位數的年份。當剖
  析兩位數的年份時，它們會根據 POSIX 和 ISO C 標準進行轉換：69--99 的
  值對映到 1969--1999，0--68 的值對映到 2000--2068。

* UTC 是 Coordinated Universal Time --- 世界協調時間（原稱為格林威治標
  準時間，或 GMT）。縮寫 UTC 並不是寫錯，而是英文和法文之間折衷的結果
  。

* DST 是 Daylight Saving Time（日光節約時間），一年中的某些時段（通常
  ）將會時區調整一小時。DST 的規則是根據當地法律決定的，且可能每年不同
  。C 函式庫有一個包含當地規則的表（通常會為了靈活性而從系統文件中讀取
  ），在這方面是唯一的真正依據。

* 各種即時 (real-time) 函式的精確度可能低於其值或引數所表示的單位所建
  議的精確度。例如，在大多數 Unix 系統上，時鐘每秒只「跳」50 次或 100
  次。

* On the other hand, the precision of "time()" and "sleep()" is better
  than their Unix equivalents: times are expressed as floating-point
  numbers, "time()" returns the most accurate time available (using
  Unix "gettimeofday()" where available), and "sleep()" will accept a
  time with a nonzero fraction (Unix "select()" is used to implement
  this, where available).

* 由 "gmtime()"、"localtime()" 和 "strptime()" 回傳，並由 "asctime()"
  、"mktime()" 和 "strftime()" 接受的時間值，是一個 9 個整數的序列。
  "gmtime()"、"localtime()" 和 "strptime()" 的回傳值也為各個欄位提供屬
  性名稱。

  關於這些物件的敘述請見 "struct_time"。

  在 3.3 版的變更: 當平台支援對應的 "struct tm" 成員時，"struct_time"
  型別被擴展以提供 "tm_gmtoff" 和 "tm_zone" 屬性。

  在 3.6 版的變更: "struct_time" 的屬性 "tm_gmtoff" 和 "tm_zone" 現在
  在所有平台上都可用。

* 使用以下函式在時間表示之間進行轉換：

  +---------------------------+---------------------------+---------------------------+
  | 轉換來源                  | 轉換目標                  | 使用                      |
  |===========================|===========================|===========================|
  | 紀元秒數                  | 世界協調時間的            | "gmtime()"                |
  |                           | "struct_time"             |                           |
  +---------------------------+---------------------------+---------------------------+
  | 紀元秒數                  | 本地時間的 "struct_time"  | "localtime()"             |
  +---------------------------+---------------------------+---------------------------+
  | 世界協調時間的            | 紀元秒數                  | "calendar.timegm()"       |
  | "struct_time"             |                           |                           |
  +---------------------------+---------------------------+---------------------------+
  | 本地時間的 "struct_time"  | 紀元秒數                  | "mktime()"                |
  +---------------------------+---------------------------+---------------------------+


函式
====

time.asctime([t])

   將由 "gmtime()" 或 "localtime()" 回傳的元組或 "struct_time" 表示的
   時間轉換為以下格式的字串："'Sun Jun 20 23:21:05 1993'"。日期欄位為
   兩個字元長，如果日期是個位數，則用空格填充，例如："'Wed Jun  9
   04:26:40 1993'"。

   如果沒有提供 *t*，則使用由 "localtime()" 回傳的當前時間。
   "asctime()" 不使用區域資訊。

   備註:

     與同名的 C 函式不同，"asctime()" 不會添加結尾的換行字元。

time.pthread_getcpuclockid(thread_id)

   為指定的 *thread_id* 回傳執行緒專用 CPU-time 時鐘的 *clk_id*。

   使用 "threading.get_ident()" 或 "threading.Thread" 物件的 "ident"
   屬性來獲取適用於 *thread_id* 的值。

   警告:

     傳遞無效或過期的 *thread_id* 可能會導致未定義的行為，例如分段錯誤
     (segmentation fault)。

   適用：Unix

   若需更多資訊，請參閱 *pthread_getcpuclockid(3)* 的說明文件。

   在 3.7 版被加入.

time.clock_getres(clk_id)

   回傳指定時鐘 *clk_id* 的解析度（精確度）。有關 *clk_id* 可接受的值
   的串列，請參閱 Clock ID Constants。

   適用：Unix。

   在 3.3 版被加入.

time.clock_gettime(clk_id) -> float

   回傳指定時鐘 *clk_id* 的時間。有關 *clk_id* 可接受的值的串列，請參
   閱 Clock ID Constants。

   使用 "clock_gettime_ns()" 以避免 "float" 型別造成的精確度損失。

   適用：Unix。

   在 3.3 版被加入.

time.clock_gettime_ns(clk_id) -> int

   類似於 "clock_gettime()"，但回傳以奈秒 (nanoseconds) 為單位的時間。

   適用：Unix。

   在 3.7 版被加入.

time.clock_settime(clk_id, time: float)

   設定指定時鐘 *clk_id* 的時間。目前，"CLOCK_REALTIME" 是 *clk_id* 唯
   一可以接受的值。

   使用 "clock_settime_ns()" 以避免 "float" 型別造成的精確度損失。

   適用：Unix。

   在 3.3 版被加入.

time.clock_settime_ns(clk_id, time: int)

   類似於 "clock_settime()"，但設定以奈秒為單位的時間。

   適用：Unix。

   在 3.7 版被加入.

time.ctime([secs])

   將自 epoch 起以秒表示的時間轉換為表示當地時間且符合以下格式的字串：
   "'Sun Jun 20 23:21:05 1993'"。日期欄位為兩個字元長，如果日期是個位
   數，則用空格填充，例如："'Wed Jun  9 04:26:40 1993'"。

   如果未提供 *secs* 或其為 "None"，則使用由 "time()" 回傳的當前時間。
   "ctime(secs)" 等同於 "asctime(localtime(secs))"。"ctime()" 不使用區
   域資訊。

time.get_clock_info(name)

   獲取指定時鐘的資訊作為命名空間物件。支援的時鐘名稱及讀取他們的值的
   對應函式如下：

   * "'monotonic'"："time.monotonic()"

   * "'perf_counter'"："time.perf_counter()"

   * "'process_time'"："time.process_time()"

   * "'thread_time'"："time.thread_time()"

   * "'time'"："time.time()"

   其結果具有以下屬性：

   * *adjustable*: 如果時鐘可以自動（例如，透過 NTP 常駐程式）或由系統
     管理員手動更改，則為 "True"，否則為 "False"

   * *implementation*: 用於獲取時鐘的值的底層 C 函式名稱。有關可能的值
     ，請參閱 Clock ID Constants。

   * *monotonic*: 如果時鐘不能倒轉，則為 "True"，否則為 "False"

   * *resolution*: 以秒 ("float") 為單位的時鐘的解析度

   在 3.3 版被加入.

time.gmtime([secs])

   將自 epoch 起以秒表示的時間轉換為 UTC 中的 "struct_time"，其中 dst
   旗標始終為零。如果未提供 *secs* 或其為 "None"，則使用由 "time()" 回
   傳的當前時間。忽略秒的分數部分。關於 "struct_time" 物件的描述，請參
   閱上文。此函式的反運算請參閱 "calendar.timegm()"。

time.localtime([secs])

   類似於 "gmtime()"，但轉換為當地時間。如果未提供 *secs* 或其為
   "None"，則使用由 "time()" 回傳的當前時間。當 DST 適用於給定時間時，
   dst 旗標會被設定為 "1"。

   如果時間戳超出 C 平台的 "localtime()" 或 "gmtime()" 函式支援的範圍
   ，"localtime()" 可能會引發 "OverflowError"；在 "localtime()" 或
   "gmtime()" 失敗時，會引發 "OSError"。通常會把年份限制在 1970 年到
   2038 年之間。

time.mktime(t)

   This is the inverse function of "localtime()".  Its argument is the
   "struct_time" or full 9-tuple (since the dst flag is needed; use
   "-1" as the dst flag if it is unknown) which expresses the time in
   *local* time, not UTC.  It returns a floating-point number, for
   compatibility with "time()". If the input value cannot be
   represented as a valid time, either "OverflowError" or "ValueError"
   will be raised (which depends on whether the invalid value is
   caught by Python or the underlying C libraries). The earliest date
   for which it can generate a time is platform-dependent.

time.monotonic() -> float

   Return the value (in fractional seconds) of a monotonic clock, i.e.
   a clock that cannot go backwards.  The clock is not affected by
   system clock updates. The reference point of the returned value is
   undefined, so that only the difference between the results of two
   calls is valid.

   Use "monotonic_ns()" to avoid the precision loss caused by the
   "float" type.

   在 3.3 版被加入.

   在 3.5 版的變更: The function is now always available and always
   system-wide.

   在 3.10 版的變更: On macOS, the function is now system-wide.

time.monotonic_ns() -> int

   Similar to "monotonic()", but return time as nanoseconds.

   在 3.7 版被加入.

time.perf_counter() -> float

   Return the value (in fractional seconds) of a performance counter,
   i.e. a clock with the highest available resolution to measure a
   short duration.  It does include time elapsed during sleep and is
   system-wide.  The reference point of the returned value is
   undefined, so that only the difference between the results of two
   calls is valid.

   Use "perf_counter_ns()" to avoid the precision loss caused by the
   "float" type.

   在 3.3 版被加入.

   在 3.10 版的變更: On Windows, the function is now system-wide.

time.perf_counter_ns() -> int

   Similar to "perf_counter()", but return time as nanoseconds.

   在 3.7 版被加入.

time.process_time() -> float

   Return the value (in fractional seconds) of the sum of the system
   and user CPU time of the current process.  It does not include time
   elapsed during sleep.  It is process-wide by definition.  The
   reference point of the returned value is undefined, so that only
   the difference between the results of two calls is valid.

   Use "process_time_ns()" to avoid the precision loss caused by the
   "float" type.

   在 3.3 版被加入.

time.process_time_ns() -> int

   Similar to "process_time()" but return time as nanoseconds.

   在 3.7 版被加入.

time.sleep(secs)

   Suspend execution of the calling thread for the given number of
   seconds. The argument may be a floating-point number to indicate a
   more precise sleep time.

   If the sleep is interrupted by a signal and no exception is raised
   by the signal handler, the sleep is restarted with a recomputed
   timeout.

   The suspension time may be longer than requested by an arbitrary
   amount, because of the scheduling of other activity in the system.

   On Windows, if *secs* is zero, the thread relinquishes the
   remainder of its time slice to any other thread that is ready to
   run. If there are no other threads ready to run, the function
   returns immediately, and the thread continues execution.  On
   Windows 8.1 and newer the implementation uses a high-resolution
   timer which provides resolution of 100 nanoseconds. If *secs* is
   zero, "Sleep(0)" is used.

   Unix implementation:

   * Use "clock_nanosleep()" if available (resolution: 1 nanosecond);

   * Or use "nanosleep()" if available (resolution: 1 nanosecond);

   * Or use "select()" (resolution: 1 microsecond).

   在 3.5 版的變更: The function now sleeps at least *secs* even if
   the sleep is interrupted by a signal, except if the signal handler
   raises an exception (see **PEP 475** for the rationale).

   在 3.11 版的變更: On Unix, the "clock_nanosleep()" and
   "nanosleep()" functions are now used if available. On Windows, a
   waitable timer is now used.

time.strftime(format[, t])

   Convert a tuple or "struct_time" representing a time as returned by
   "gmtime()" or "localtime()" to a string as specified by the
   *format* argument.  If *t* is not provided, the current time as
   returned by "localtime()" is used.  *format* must be a string.
   "ValueError" is raised if any field in *t* is outside of the
   allowed range.

   0 is a legal argument for any position in the time tuple; if it is
   normally illegal the value is forced to a correct one.

   The following directives can be embedded in the *format* string.
   They are shown without the optional field width and precision
   specification, and are replaced by the indicated characters in the
   "strftime()" result:

   +-------------+--------------------------------------------------+---------+
   | Directive   | Meaning                                          | 註解    |
   |=============|==================================================|=========|
   | "%a"        | Locale's abbreviated weekday name.               |         |
   +-------------+--------------------------------------------------+---------+
   | "%A"        | Locale's full weekday name.                      |         |
   +-------------+--------------------------------------------------+---------+
   | "%b"        | Locale's abbreviated month name.                 |         |
   +-------------+--------------------------------------------------+---------+
   | "%B"        | Locale's full month name.                        |         |
   +-------------+--------------------------------------------------+---------+
   | "%c"        | Locale's appropriate date and time               |         |
   |             | representation.                                  |         |
   +-------------+--------------------------------------------------+---------+
   | "%d"        | Day of the month as a decimal number [01,31].    |         |
   +-------------+--------------------------------------------------+---------+
   | "%f"        | Microseconds as a decimal number                 | (1)     |
   |             | [000000,999999].                                 |         |
   +-------------+--------------------------------------------------+---------+
   | "%H"        | Hour (24-hour clock) as a decimal number         |         |
   |             | [00,23].                                         |         |
   +-------------+--------------------------------------------------+---------+
   | "%I"        | Hour (12-hour clock) as a decimal number         |         |
   |             | [01,12].                                         |         |
   +-------------+--------------------------------------------------+---------+
   | "%j"        | Day of the year as a decimal number [001,366].   |         |
   +-------------+--------------------------------------------------+---------+
   | "%m"        | Month as a decimal number [01,12].               |         |
   +-------------+--------------------------------------------------+---------+
   | "%M"        | Minute as a decimal number [00,59].              |         |
   +-------------+--------------------------------------------------+---------+
   | "%p"        | Locale's equivalent of either AM or PM.          | (2)     |
   +-------------+--------------------------------------------------+---------+
   | "%S"        | Second as a decimal number [00,61].              | (3)     |
   +-------------+--------------------------------------------------+---------+
   | "%U"        | Week number of the year (Sunday as the first day | (4)     |
   |             | of the week) as a decimal number [00,53]. All    |         |
   |             | days in a new year preceding the first Sunday    |         |
   |             | are considered to be in week 0.                  |         |
   +-------------+--------------------------------------------------+---------+
   | "%w"        | Weekday as a decimal number [0(Sunday),6].       |         |
   +-------------+--------------------------------------------------+---------+
   | "%W"        | Week number of the year (Monday as the first day | (4)     |
   |             | of the week) as a decimal number [00,53]. All    |         |
   |             | days in a new year preceding the first Monday    |         |
   |             | are considered to be in week 0.                  |         |
   +-------------+--------------------------------------------------+---------+
   | "%x"        | Locale's appropriate date representation.        |         |
   +-------------+--------------------------------------------------+---------+
   | "%X"        | Locale's appropriate time representation.        |         |
   +-------------+--------------------------------------------------+---------+
   | "%y"        | Year without century as a decimal number         |         |
   |             | [00,99].                                         |         |
   +-------------+--------------------------------------------------+---------+
   | "%Y"        | Year with century as a decimal number.           |         |
   +-------------+--------------------------------------------------+---------+
   | "%z"        | Time zone offset indicating a positive or        |         |
   |             | negative time difference from UTC/GMT of the     |         |
   |             | form +HHMM or -HHMM, where H represents decimal  |         |
   |             | hour digits and M represents decimal minute      |         |
   |             | digits [-23:59, +23:59]. [1]                     |         |
   +-------------+--------------------------------------------------+---------+
   | "%Z"        | Time zone name (no characters if no time zone    |         |
   |             | exists). Deprecated. [1]                         |         |
   +-------------+--------------------------------------------------+---------+
   | "%%"        | A literal "'%'" character.                       |         |
   +-------------+--------------------------------------------------+---------+

   註解：

   1. The "%f" format directive only applies to "strptime()", not to
      "strftime()". However, see also "datetime.datetime.strptime()"
      and "datetime.datetime.strftime()" where the "%f" format
      directive applies to microseconds.

   2. When used with the "strptime()" function, the "%p" directive
      only affects the output hour field if the "%I" directive is used
      to parse the hour.

   3. The range really is "0" to "61"; value "60" is valid in
      timestamps representing leap seconds and value "61" is supported
      for historical reasons.

   4. When used with the "strptime()" function, "%U" and "%W" are only
      used in calculations when the day of the week and the year are
      specified.

   Here is an example, a format for dates compatible with that
   specified  in the **RFC 2822** Internet email standard.  [1]

      >>> from time import gmtime, strftime
      >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
      'Thu, 28 Jun 2001 14:17:15 +0000'

   Additional directives may be supported on certain platforms, but
   only the ones listed here have a meaning standardized by ANSI C.
   To see the full set of format codes supported on your platform,
   consult the *strftime(3)* documentation.

   On some platforms, an optional field width and precision
   specification can immediately follow the initial "'%'" of a
   directive in the following order; this is also not portable. The
   field width is normally 2 except for "%j" where it is 3.

time.strptime(string[, format])

   Parse a string representing a time according to a format.  The
   return value is a "struct_time" as returned by "gmtime()" or
   "localtime()".

   The *format* parameter uses the same directives as those used by
   "strftime()"; it defaults to ""%a %b %d %H:%M:%S %Y"" which matches
   the formatting returned by "ctime()". If *string* cannot be parsed
   according to *format*, or if it has excess data after parsing,
   "ValueError" is raised. The default values used to fill in any
   missing data when more accurate values cannot be inferred are
   "(1900, 1, 1, 0, 0, 0, 0, 1, -1)". Both *string* and *format* must
   be strings.

   For example:

   >>> import time
   >>> time.strptime("30 Nov 00", "%d %b %y")   
   time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
                    tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)

   Support for the "%Z" directive is based on the values contained in
   "tzname" and whether "daylight" is true.  Because of this, it is
   platform-specific except for recognizing UTC and GMT which are
   always known (and are considered to be non-daylight savings
   timezones).

   Only the directives specified in the documentation are supported.
   Because "strftime()" is implemented per platform it can sometimes
   offer more directives than those listed.  But "strptime()" is
   independent of any platform and thus does not necessarily support
   all directives available that are not documented as supported.

class time.struct_time

   The type of the time value sequence returned by "gmtime()",
   "localtime()", and "strptime()".  It is an object with a *named
   tuple* interface: values can be accessed by index and by attribute
   name.  The following values are present:

   +-----------------------------------+-----------------------------------+-----------------------------------+
   | Index                             | 屬性                              | Values                            |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 0                                 | tm_year                           | （例如 1993）                     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 1                                 | tm_mon                            | range [1, 12]                     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 2                                 | tm_mday                           | range [1, 31]                     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 3                                 | tm_hour                           | range [0, 23]                     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 4                                 | tm_min                            | range [0, 59]                     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 5                                 | tm_sec                            | range [0, 61]; see Note (2) in    |
   |                                   |                                   | "strftime()"                      |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 6                                 | tm_wday                           | range [0, 6]; Monday is 0         |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 7                                 | tm_yday                           | range [1, 366]                    |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | 8                                 | tm_isdst                          | 0, 1 or -1; see below             |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | N/A                               | tm_zone                           | abbreviation of timezone name     |
   +-----------------------------------+-----------------------------------+-----------------------------------+
   | N/A                               | tm_gmtoff                         | offset east of UTC in seconds     |
   +-----------------------------------+-----------------------------------+-----------------------------------+

   Note that unlike the C structure, the month value is a range of [1,
   12], not [0, 11].

   In calls to "mktime()", "tm_isdst" may be set to 1 when daylight
   savings time is in effect, and 0 when it is not.  A value of -1
   indicates that this is not known, and will usually result in the
   correct state being filled in.

   When a tuple with an incorrect length is passed to a function
   expecting a "struct_time", or having elements of the wrong type, a
   "TypeError" is raised.

time.time() -> float

   Return the time in seconds since the epoch as a floating-point
   number. The handling of leap seconds is platform dependent. On
   Windows and most Unix systems, the leap seconds are not counted
   towards the time in seconds since the epoch. This is commonly
   referred to as Unix time.

   Note that even though the time is always returned as a floating-
   point number, not all systems provide time with a better precision
   than 1 second. While this function normally returns non-decreasing
   values, it can return a lower value than a previous call if the
   system clock has been set back between the two calls.

   The number returned by "time()" may be converted into a more common
   time format (i.e. year, month, day, hour, etc...) in UTC by passing
   it to "gmtime()" function or in local time by passing it to the
   "localtime()" function. In both cases a "struct_time" object is
   returned, from which the components of the calendar date may be
   accessed as attributes.

   Use "time_ns()" to avoid the precision loss caused by the "float"
   type.

time.time_ns() -> int

   Similar to "time()" but returns time as an integer number of
   nanoseconds since the epoch.

   在 3.7 版被加入.

time.thread_time() -> float

   Return the value (in fractional seconds) of the sum of the system
   and user CPU time of the current thread.  It does not include time
   elapsed during sleep.  It is thread-specific by definition.  The
   reference point of the returned value is undefined, so that only
   the difference between the results of two calls in the same thread
   is valid.

   Use "thread_time_ns()" to avoid the precision loss caused by the
   "float" type.

   適用：Linux、Unix、Windows。

   Unix systems supporting "CLOCK_THREAD_CPUTIME_ID".

   在 3.7 版被加入.

time.thread_time_ns() -> int

   Similar to "thread_time()" but return time as nanoseconds.

   在 3.7 版被加入.

time.tzset()

   Reset the time conversion rules used by the library routines. The
   environment variable "TZ" specifies how this is done. It will also
   set the variables "tzname" (from the "TZ" environment variable),
   "timezone" (non-DST seconds West of UTC), "altzone" (DST seconds
   west of UTC) and "daylight" (to 0 if this timezone does not have
   any daylight saving time rules, or to nonzero if there is a time,
   past, present or future when daylight saving time applies).

   適用：Unix。

   備註:

     Although in many cases, changing the "TZ" environment variable
     may affect the output of functions like "localtime()" without
     calling "tzset()", this behavior should not be relied on.The "TZ"
     environment variable should contain no whitespace.

   The standard format of the "TZ" environment variable is (whitespace
   added for clarity):

      std offset [dst [offset [,start[/time], end[/time]]]]

   Where the components are:

   "std" 和 "dst"
      Three or more alphanumerics giving the timezone abbreviations.
      These will be propagated into time.tzname

   "offset"
      The offset has the form: "± hh[:mm[:ss]]". This indicates the
      value added the local time to arrive at UTC.  If preceded by a
      '-', the timezone is east of the Prime Meridian; otherwise, it
      is west. If no offset follows dst, summer time is assumed to be
      one hour ahead of standard time.

   "start[/time], end[/time]"
      Indicates when to change to and back from DST. The format of the
      start and end dates are one of the following:

      "J*n*"
         The Julian day *n* (1 <= *n* <= 365). Leap days are not
         counted, so in all years February 28 is day 59 and March 1 is
         day 60.

      "*n*"
         The zero-based Julian day (0 <= *n* <= 365). Leap days are
         counted, and it is possible to refer to February 29.

      "M*m*.*n*.*d*"
         The *d*'th day (0 <= *d* <= 6) of week *n* of month *m* of
         the year (1 <= *n* <= 5, 1 <= *m* <= 12, where week 5 means
         "the last *d* day in month *m*" which may occur in either the
         fourth or the fifth week). Week 1 is the first week in which
         the *d*'th day occurs. Day zero is a Sunday.

      "time" has the same format as "offset" except that no leading
      sign ('-' or '+') is allowed. The default, if time is not given,
      is 02:00:00.

      >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
      >>> time.tzset()
      >>> time.strftime('%X %x %Z')
      '02:07:36 05/08/03 EDT'
      >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
      >>> time.tzset()
      >>> time.strftime('%X %x %Z')
      '16:08:12 05/08/03 AEST'

   On many Unix systems (including *BSD, Linux, Solaris, and Darwin),
   it is more convenient to use the system's zoneinfo (*tzfile(5)*)
   database to specify the timezone rules. To do this, set the  "TZ"
   environment variable to the path of the required timezone
   datafile, relative to the root of the systems 'zoneinfo' timezone
   database, usually located at "/usr/share/zoneinfo". For example,
   "'US/Eastern'", "'Australia/Melbourne'", "'Egypt'" or
   "'Europe/Amsterdam'".

      >>> os.environ['TZ'] = 'US/Eastern'
      >>> time.tzset()
      >>> time.tzname
      ('EST', 'EDT')
      >>> os.environ['TZ'] = 'Egypt'
      >>> time.tzset()
      >>> time.tzname
      ('EET', 'EEST')


Clock ID Constants
==================

These constants are used as parameters for "clock_getres()" and
"clock_gettime()".

time.CLOCK_BOOTTIME

   Identical to "CLOCK_MONOTONIC", except it also includes any time
   that the system is suspended.

   This allows applications to get a suspend-aware monotonic  clock
   without having to deal with the complications of "CLOCK_REALTIME",
   which may have  discontinuities if the time is changed using
   "settimeofday()" or similar.

   適用：Linux 2.6.39 以上。

   在 3.7 版被加入.

time.CLOCK_HIGHRES

   The Solaris OS has a "CLOCK_HIGHRES" timer that attempts to use an
   optimal hardware source, and may give close to nanosecond
   resolution. "CLOCK_HIGHRES" is the nonadjustable, high-resolution
   clock.

   適用：Solaris。

   在 3.3 版被加入.

time.CLOCK_MONOTONIC

   Clock that cannot be set and represents monotonic time since some
   unspecified starting point.

   適用：Unix。

   在 3.3 版被加入.

time.CLOCK_MONOTONIC_RAW

   Similar to "CLOCK_MONOTONIC", but provides access to a raw
   hardware-based time that is not subject to NTP adjustments.

   適用：Linux 2.6.28 以上、macOS 10.12 以上。

   在 3.3 版被加入.

time.CLOCK_PROCESS_CPUTIME_ID

   High-resolution per-process timer from the CPU.

   適用：Unix。

   在 3.3 版被加入.

time.CLOCK_PROF

   High-resolution per-process timer from the CPU.

   適用：FreeBSD、NetBSD 7 以上、OpenBSD。

   在 3.7 版被加入.

time.CLOCK_TAI

   International Atomic Time

   The system must have a current leap second table in order for this
   to give the correct answer.  PTP or NTP software can maintain a
   leap second table.

   適用：Linux。

   在 3.9 版被加入.

time.CLOCK_THREAD_CPUTIME_ID

   Thread-specific CPU-time clock.

   適用：Unix。

   在 3.3 版被加入.

time.CLOCK_UPTIME

   Time whose absolute value is the time the system has been running
   and not suspended, providing accurate uptime measurement, both
   absolute and interval.

   適用：FreeBSD、OpenBSD 5.5 以上。

   在 3.7 版被加入.

time.CLOCK_UPTIME_RAW

   Clock that increments monotonically, tracking the time since an
   arbitrary point, unaffected by frequency or time adjustments and
   not incremented while the system is asleep.

   適用：macOS 10.12 以上。

   在 3.8 版被加入.

The following constant is the only parameter that can be sent to
"clock_settime()".

time.CLOCK_REALTIME

   System-wide real-time clock.  Setting this clock requires
   appropriate privileges.

   適用：Unix。

   在 3.3 版被加入.


Timezone Constants
==================

time.altzone

   The offset of the local DST timezone, in seconds west of UTC, if
   one is defined. This is negative if the local DST timezone is east
   of UTC (as in Western Europe, including the UK).  Only use this if
   "daylight" is nonzero.  See note below.

time.daylight

   Nonzero if a DST timezone is defined.  See note below.

time.timezone

   The offset of the local (non-DST) timezone, in seconds west of UTC
   (negative in most of Western Europe, positive in the US, zero in
   the UK).  See note below.

time.tzname

   A tuple of two strings: the first is the name of the local non-DST
   timezone, the second is the name of the local DST timezone.  If no
   DST timezone is defined, the second string should not be used.  See
   note below.

備註:

  For the above Timezone constants ("altzone", "daylight", "timezone",
  and "tzname"), the value is determined by the timezone rules in
  effect at module load time or the last time "tzset()" is called and
  may be incorrect for times in the past.  It is recommended to use
  the "tm_gmtoff" and "tm_zone" results from "localtime()" to obtain
  timezone information.

也參考:

  "datetime" 模組
     More object-oriented interface to dates and times.

  "locale" 模組
     Internationalization services.  The locale setting affects the
     interpretation of many format specifiers in "strftime()" and
     "strptime()".

  "calendar" 模組
     General calendar-related functions.   "timegm()" is the inverse
     of "gmtime()" from this module.

-[ 註解 ]-

[1] The use of "%Z" is now deprecated, but the "%z" escape that
    expands to the preferred hour/minute offset is not supported by
    all ANSI C libraries. Also, a strict reading of the original 1982
    **RFC 822** standard calls for a two-digit year ("%y" rather than
    "%Y"), but practice moved to 4-digit years long before the year
    2000.  After that, **RFC 822** became obsolete and the 4-digit
    year has been first recommended by **RFC 1123** and then mandated
    by **RFC 2822**.
