16.3. time — 时间的访问和转换 ¶

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此模块提供各种时间相关函数。对于相关功能，另请参阅 datetime and calendar 模块。

Although this module is always available, not all functions are available on all platforms. Most of the functions defined in this module call platform C library functions with the same name. It may sometimes be helpful to consult the platform documentation, because the semantics of these functions varies among platforms.

按次序解释一些术语和约定。

• The epoch is the point where the time starts, and is platform dependent. For Unix, the epoch is January 1, 1970, 00:00:00 (UTC). To find out what the epoch is on a given platform, look at time.gmtime(0) .

• 术语 从纪元起的秒数 refers to the total number of elapsed seconds since the epoch, typically excluding 闰秒 . Leap seconds are excluded from this total on all POSIX-compliant platforms.

• The functions in this module may not handle dates and times before the epoch or far in the future. The cut-off point in the future is determined by the C library; for 32-bit systems, it is typically in 2038.

• 2000 年 (Y2K) 问题 : Python depends on the platform’s C library, which generally doesn’t have year 2000 issues, since all dates and times are represented internally as seconds since the epoch. Function strptime() can parse 2-digit years when given %y format code. When 2-digit years are parsed, they are converted according to the POSIX and ISO C standards: values 69–99 are mapped to 1969–1999, and values 0–68 are mapped to 2000–2068.

• UTC is Coordinated Universal Time (formerly known as Greenwich Mean Time, or GMT). The acronym UTC is not a mistake but a compromise between English and French.

• DST is Daylight Saving Time, an adjustment of the timezone by (usually) one hour during part of the year. DST rules are magic (determined by local law) and can change from year to year. The C library has a table containing the local rules (often it is read from a system file for flexibility) and is the only source of True Wisdom in this respect.

• The precision of the various real-time functions may be less than suggested by the units in which their value or argument is expressed. E.g. on most Unix systems, the clock “ticks” only 50 or 100 times a second.

• 另一方面，精度对于 time() and sleep() 比它们的 Unix 等价要好：时间以浮点数形式表达， time() 返回最精确可用时间 (使用 Unix gettimeofday() 若可用)，而 sleep() 将接受具有非零小数的时间 (Unix select() 用于实现这，若可用)。

• 时间值如返回通过 gmtime() , localtime() ，和 strptime() ，和接受通过 asctime() , mktime() and strftime() ，是 9 整数序列。返回值的 gmtime() , localtime() ，和 strptime() 还为单个字段提供属性名。

  见 struct_time 了解这些对象的描述。

  3.3 版改变： The struct_time 类型被扩展以提供 tm_gmtoff and tm_zone 属性当平台支持相应 struct tm 成员。

• 使用下列函数在时间表示之间转换：

  从	到	使用
  从纪元起的秒数	struct_time in UTC	gmtime()
  从纪元起的秒数	struct_time in local time	localtime()
  struct_time in UTC	从纪元起的秒数	calendar.timegm()
  struct_time in local time	从纪元起的秒数	mktime()

The module defines the following functions and data items:

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.

time. asctime ( [ t ] ) ¶

转换元组或 struct_time 表示时间如返回通过 gmtime() or localtime() to a string of the following form: 'Sun Jun 20 23:21:05 1993' 。若 t 不提供，当前时间如返回通过 localtime() is used. Locale information is not used by asctime() .

注意

不像同名 C 函数， asctime() 不添加结尾换行符。

time. clock ( ) ¶

On Unix, return the current processor time as a floating point number expressed in seconds. The precision, and in fact the very definition of the meaning of “processor time”, depends on that of the C function of the same name.

On Windows, this function returns wall-clock seconds elapsed since the first call to this function, as a floating point number, based on the Win32 function QueryPerformanceCounter() . The resolution is typically better than one microsecond.

从 3.3 版起弃用： The behaviour of this function depends on the platform: use perf_counter() or process_time() instead, depending on your requirements, to have a well defined behaviour.

time. clock_getres ( clk_id ) ¶

Return the resolution (precision) of the specified clock clk_id .

可用性：Unix。

3.3 版新增。

time. clock_gettime ( clk_id ) ¶

Return the time of the specified clock clk_id .

可用性：Unix。

3.3 版新增。

time. clock_settime ( clk_id , time ) ¶

Set the time of the specified clock clk_id .

可用性：Unix。

3.3 版新增。

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.

可用性：Solaris。

3.3 版新增。

time. CLOCK_MONOTONIC ¶

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

可用性：Unix。

3.3 版新增。

time. CLOCK_MONOTONIC_RAW ¶

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

Availability: Linux 2.6.28 or later.

3.3 版新增。

time. CLOCK_PROCESS_CPUTIME_ID ¶

High-resolution per-process timer from the CPU.

可用性：Unix。

3.3 版新增。

time. CLOCK_REALTIME ¶

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

可用性：Unix。

3.3 版新增。

time. CLOCK_THREAD_CPUTIME_ID ¶

特定线程的 CPU 时间时钟。

可用性：Unix。

3.3 版新增。

time. ctime ( [ secs ] ) ¶

Convert a time expressed in seconds since the epoch to a string representing local time. If secs 不提供或 None ，当前时间若返回通过 time() 被使用。 ctime(secs) 相当于 asctime(localtime(secs)) 。不使用区域设置信息通过 ctime() .

time. daylight ¶

Nonzero if a DST timezone is defined.

time. get_clock_info ( name ) ¶

以名称空间对象形式获取指定时钟有关信息。支持的时钟名称和要读取其值的相应函数是：

• 'clock' : time.clock()
• 'monotonic' : time.monotonic()
• 'perf_counter' : time.perf_counter()
• 'process_time' : time.process_time()
• 'time' : time.time()

结果拥有下列属性：

• adjustable : True if the clock can be changed automatically (e.g. by a NTP daemon) or manually by the system administrator, False 否则
• 实现 : The name of the underlying C function used to get the clock value
• monotonic : True 若时钟无法后退， False 否则
• resolution ：以秒为单位的时钟分辨率 ( float )

3.3 版新增。

time. gmtime ( [ secs ] ) ¶

Convert a time expressed in seconds since the epoch to a struct_time in UTC in which the dst flag is always zero. If secs 不提供或 None ，当前时间若返回通过 time() is used. Fractions of a second are ignored. See above for a description of the struct_time 对象。见 calendar.timegm() for the inverse of this function.

time. localtime ( [ secs ] ) ¶

像 gmtime() 但转换为本地时间。若 secs 不提供或 None ，当前时间若返回通过 time() 的使用。dst 标志被设为 1 当 DST (夏令时) 适用于给定时间时。

time. mktime ( t ) ¶

这是逆函数对于 localtime() 。它的自变量为 struct_time 或完整 9 元组 (由于需要 dst 标志；使用 -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 ( ) ¶

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 consecutive calls is valid.

On Windows versions older than Vista, monotonic() detects GetTickCount() integer overflow (32 bits, roll-over after 49.7 days). It increases an internal epoch (reference time) by 2 ³² each time that an overflow is detected. The epoch is stored in the process-local state and so the value of monotonic() may be different in two Python processes running for more than 49 days. On more recent versions of Windows and on other operating systems, monotonic() is system-wide.

3.3 版新增。

3.5 版改变： 函数现在始终可用。

time. perf_counter ( ) ¶

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 consecutive calls is valid.

3.3 版新增。

time. process_time ( ) ¶

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 consecutive calls is valid.

3.3 版新增。

time. sleep ( secs ) ¶

按给定秒数挂起调用线程的执行。自变量可以是浮点数，以指示更准确休眠时间。实际挂起时间可能小于请求，因为任何捕获信号都会终止 sleep() 之后执行相应信号的捕获例程。此外，挂起时间可能长于任意请求数量，由于其它系统活动的调度。

3.5 版改变： 函数现在休眠至少 secs 即使休眠被信号中断，除信号处理程序引发异常外 (见 PEP 475 了解基本原理)。

time. strftime ( format [ , t ] ) ¶

转换元组或 struct_time 表示时间如返回通过 gmtime() or localtime() 到字符串作为指定通过 format 自变量。若 t 不提供，当前时间如返回通过 localtime() 被使用。 format 必须是字符串。 ValueError 被引发若任何字段在 t 超出允许范围。

0 是时间元组中任何位置的合法自变量；若它非法，通常被强制为正确值。

下列指令可以嵌入 format 字符串。它们被展示时没有可选字段宽度和精度规范，并替换指示字符在 strftime() 结果：

指令	含义	注意事项
%a	区域设置的缩写工作日名称。
%A	区域设置的完整工作日名称。
%b	区域设置的缩写月份名。
%B	区域设置的完整月份名。
%c	Locale’s appropriate date and time 表示。
%d	月份日期如十进制数 [01, 31]。
%H	Hour (24-hour clock) as a decimal number [00,23].
%I	Hour (12-hour clock) as a decimal number [01,12].
%j	年内天数如十进制数 [001, 366]。
%m	月份如十进制数 [01, 12]。
%M	分钟如十进制数 [00, 59]。
%p	区域设置的 AM 或 PM 等价。	(1)
%S	秒如十进制数 [00, 61]。	(2)
%U	Week number of the year (Sunday as the first day 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.	(3)
%w	工作日如十进制数 [0 (星期日）, 6]。
%W	Week number of the year (Monday as the first day 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.	(3)
%x	区域设置的适当日期表示。
%X	区域设置的适当时间表示。
%y	Year without century as a decimal number [00,99].
%Y	带有世纪的年份如十进制数。
%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].
%Z	Time zone name (no characters if no time zone exists).
%%	文字 '%' 字符。

注意事项：

1. 当用于 strptime() 函数， %p directive only affects the output hour field if the %I directive is used to parse the hour.
2. The range really is 0 to 61 ；值 60 is valid in timestamps representing 闰秒 和值 61 is supported for historical reasons.
3. 当用于 strptime() 函数， %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 互联网 Email 标准。 [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) 文档编制。

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 ] ) ¶

根据格式剖析表示时间的字符串。返回值为 struct_time 如返回通过 gmtime() or localtime() .

The format 参数使用相同指令如那些用于 strftime() ；默认为 "%a %b %d %H:%M:%S %Y" which matches the formatting returned by ctime() 。若 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) 。两者 string and format 必须是字符串。

例如：

>>> 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)
						

支持 %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 ¶

时间值序列类型返回通过 gmtime() , localtime() ，和 strptime() 。它是对象具有 命名元组 interface: values can be accessed by index and by attribute name. The following values are present:

索引	属性	值
0	tm_year	(例如，1993)
1	tm_mon	范围 [1, 12]
2	tm_mday	范围 [1, 31]
3	tm_hour	范围 [0, 23]
4	tm_min	范围 [0, 59]
5	tm_sec	范围 [0, 61]；见 (2) in strftime() description
6	tm_wday	range [0, 6]，星期一为 0
7	tm_yday	范围 [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 被引发。

3.3 版改变： tm_gmtoff and tm_zone attributes are available on platforms with C library supporting the corresponding fields in struct tm .

time. time ( ) ¶

Return the time in seconds since the epoch as a floating point number. The specific date of the epoch and the handling of 闰秒 is platform dependent. On Windows and most Unix systems, the epoch is January 1, 1970, 00:00:00 (UTC) and leap seconds are not counted towards the time in seconds since the epoch. This is commonly referred to as Unix time . To find out what the epoch is on a given platform, look at gmtime(0) .

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.

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).

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.

time. tzset ( ) ¶

Resets the time conversion rules used by the library routines. The environment variable TZ specifies how this is done.

可用性：Unix。

注意

Although in many cases, changing the TZ environment variable may affect the output of functions like localtime() 不调用 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 and 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:

Jn

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.

Mm.n.d

The d ‘th day (0 <= d <= 6) or 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 Sunday.

time 拥有相同格式如 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 。例如， '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')
					

另请参阅

模块 datetime

更面向对象的日期和时间接口。

模块 locale

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

模块 calendar

一般日历相关功能。 timegm() 是 inverse of gmtime() 来自此模块。

脚注

[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 .

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