time
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io
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。
datetime
calendar
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 是时间起始点，返回值为 time.gmtime(0) 。在所有平台都是 1970 年 1 月 1 日 00:00:00 (UTC)。
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.
函数 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.
strptime()
%y
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)。
time()
sleep()
gettimeofday()
select()
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。
gmtime()
localtime()
asctime()
mktime()
strftime()
见 struct_time 了解这些对象的描述。
struct_time
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。
tm_gmtoff
tm_zone
struct tm
3.6 版改变： The struct_time 属性 tm_gmtoff and tm_zone 现在可用于所有平台。
使用下列函数在时间表示之间转换：
从
到
使用
struct_time 按 UTC
struct_time 按本地时间
calendar.timegm()
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' . The day field is two characters long and is space padded if the day is a single digit, e.g.: 'Wed Jun 9 04:26:40 1993' .
'Sun Jun 20 23:21:05 1993'
'Wed Jun 9 04:26:40 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。
返回 clk_id of the thread-specific CPU-time clock for the specified thread_id .
使用 threading.get_ident() 或 ident attribute of threading.Thread objects to get a suitable value for thread_id .
threading.get_ident()
ident
threading.Thread
警告
传递无效或过期 thread_id may result in undefined behavior, such as segmentation fault.
可用性 : Unix
见手册页为 pthread_getcpuclockid(3) 了解进一步信息。
Added in version 3.7.
Return the resolution (precision) of the specified clock clk_id 。参考 时钟 ID 常量 for a list of accepted values for clk_id .
可用性 ：Unix。
Added in version 3.3.
Return the time of the specified clock clk_id 。参考 时钟 ID 常量 for a list of accepted values for clk_id .
使用 clock_gettime_ns() 能避免造成精度损失按 float 类型。
clock_gettime_ns()
float
类似于 clock_gettime() 但以纳秒形式返回时间。
clock_gettime()
Set the time of the specified clock clk_id 。目前， CLOCK_REALTIME is the only accepted value for clk_id .
CLOCK_REALTIME
使用 clock_settime_ns() 能避免造成精度损失按 float 类型。
clock_settime_ns()
类似于 clock_settime() 但按纳秒设置时间。
clock_settime()
Convert a time expressed in seconds since the epoch to a string of a form: 'Sun Jun 20 23:21:05 1993' 表示本地时间。日期字段 2 字符长，并以空格填充若日期为单数字，如： 'Wed Jun 9 04:26:40 1993' .
若 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() .
None
ctime(secs)
asctime(localtime(secs))
ctime()
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：
'monotonic' : time.monotonic()
'monotonic'
time.monotonic()
'perf_counter' : time.perf_counter()
'perf_counter'
time.perf_counter()
'process_time' : time.process_time()
'process_time'
time.process_time()
'thread_time' : time.thread_time()
'thread_time'
time.thread_time()
'time' : time.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
True
False
实现 : The name of the underlying C function used to get the clock value. Refer to 时钟 ID 常量 了解可能值。
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 )
Convert a time expressed in seconds since the epoch 到 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.
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。
1
localtime() 可能引发 OverflowError , if the timestamp is outside 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 between 1970 and 2038.
OverflowError
OSError
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.
-1
ValueError
返回单调时钟的值 (以小数秒为单位)，即无法后退的时钟。时钟不受系统时钟更新的影响。返回值参考点未定义，因此仅 2 调用结果之间的差异有效。
使用 monotonic_ns() 能避免造成精度损失按 float 类型。
monotonic_ns()
3.5 版改变： 函数现在始终可用且始终系统范围。
3.10 版改变： 在 macOS，函数现在是系统范围内的。
类似于 monotonic() ，但以纳秒形式返回时间。
monotonic()
返回性能计数器的值 (以小数秒为单位)，即采用最高可用分辨率的时钟来度量短持续时间。它包括休眠期间和系统范围的消耗时间。返回值参考点未定义，因此仅 2 调用结果之间的差异有效。
使用 perf_counter_ns() 能避免造成精度损失按 float 类型。
perf_counter_ns()
3.10 版改变： 在 Windows，函数现在是系统范围内的。
类似于 perf_counter() ，但以纳秒形式返回时间。
perf_counter()
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.
使用 process_time_ns() 能避免造成精度损失按 float 类型。
process_time_ns()
类似于 process_time() 但以纳秒形式返回时间。
process_time()
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.
在 Windows，若 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 为 0， Sleep(0) 被使用。
Sleep(0)
Unix 实现：
使用 clock_nanosleep() 若可用 (分辨率：1 纳秒)；
clock_nanosleep()
或使用 nanosleep() 若可用 (分辨率：1 纳秒)；
nanosleep()
或使用 select() (分辨率：1 微秒)。
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)。
3.11 版改变： 在 Unix， clock_nanosleep() and nanosleep() functions are now used if available. On Windows, a waitable timer is now used.
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
%A
%b
%B
%c
区域设置的适当日期和时间表示。
%d
%f
[000000,999999].
%H
小时 (24 小时时钟) 如十进制数 [00, 23]。
%I
小时 (12 小时时钟) 如十进制数 [01, 12]。
%j
%m
%M
%p
%S
%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.
%w
%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.
%x
%X
不带世纪的年份如十进制数 [00, 99]。
%Y
%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 ]
%%
文字 '%' 字符。
'%'
注意事项：
The %f format directive only applies to strptime() , not to strftime() . However, see also datetime.datetime.strptime() and datetime.datetime.strftime() 在哪里 %f format directive applies to microseconds .
datetime.datetime.strptime()
datetime.datetime.strftime()
当用于 strptime() 函数， %p directive only affects the output hour field if the %I directive is used to parse the hour.
The range really is 0 to 61 ；值 60 is valid in timestamps representing 闰秒 和值 61 is supported for historical reasons.
0
61
60
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.
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。
"%a %b %d %H:%M:%S %Y"
(1900, 1, 1, 0, 0, 0, 0, 1, -1)
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).
tzname
daylight
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.
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:
范围 [0, 61]；见 Note (2) in strftime()
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.
tm_isdst
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。
TypeError
Return the time in seconds since the epoch as a floating point number. The handling of 闰秒 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.
使用 time_ns() 能避免造成精度损失按 float 类型。
time_ns()
类似于 time() but returns time as an integer number of nanoseconds since the epoch .
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.
使用 thread_time_ns() 能避免造成精度损失按 float 类型。
thread_time_ns()
可用性 ：Linux、Unix、Windows。
Unix 系统支持 CLOCK_THREAD_CPUTIME_ID .
CLOCK_THREAD_CPUTIME_ID
类似于 thread_time() 但以纳秒形式返回时间。
thread_time()
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).
TZ
timezone
altzone
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.
tzset()
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
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.
± hh[:mm[:ss]]
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) 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 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' .
/usr/share/zoneinfo
'US/Eastern'
'Australia/Melbourne'
'Egypt'
'Europe/Amsterdam'
>>> os.environ['TZ'] = 'US/Eastern' >>> time.tzset() >>> time.tzname ('EST', 'EDT') >>> os.environ['TZ'] = 'Egypt' >>> time.tzset() >>> time.tzname ('EET', 'EEST')
这些常量被用作参数为 clock_getres() and clock_gettime() .
clock_getres()
等同于 CLOCK_MONOTONIC , except it also includes any time that the system is suspended.
CLOCK_MONOTONIC
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.
settimeofday()
可用性 : Linux >= 2.6.39.
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.
CLOCK_HIGHRES
可用性 : Solaris.
Clock that cannot be set and represents monotonic time since some unspecified starting point.
类似于 CLOCK_MONOTONIC , but provides access to a raw hardware-based time that is not subject to NTP adjustments.
可用性 : Linux >= 2.6.28, macOS >= 10.12.
High-resolution per-process timer from the CPU.
可用性 : FreeBSD, NetBSD >= 7, OpenBSD.
国际原子时间
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.
可用性 ：Linux。
Added in version 3.9.
特定线程的 CPU 时间时钟。
Time whose absolute value is the time the system has been running and not suspended, providing accurate uptime measurement, both absolute and interval.
可用性 : FreeBSD, OpenBSD >= 5.5.
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.
可用性 : macOS >= 10.12.
Added in version 3.8.
The following constant is the only parameter that can be sent to clock_settime() .
System-wide real-time clock. Setting this clock requires appropriate privileges.
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.
Nonzero if a DST timezone is defined. See note below.
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.
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.
For the above Timezone constants ( altzone , daylight , timezone ，和 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.
另请参阅
更面向对象的日期和时间接口。
locale
Internationalization services. The locale setting affects the interpretation of many format specifiers in strftime() and strptime() .
一般日历相关功能。 timegm() is the inverse of gmtime() 来自此模块。
timegm()
脚注
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argparse
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