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Diffstat (limited to 'Doc/library/time.rst')
| -rw-r--r-- | Doc/library/time.rst | 223 |
1 files changed, 176 insertions, 47 deletions
diff --git a/Doc/library/time.rst b/Doc/library/time.rst index e0c7007e5b..a8c70b33ae 100644 --- a/Doc/library/time.rst +++ b/Doc/library/time.rst @@ -41,25 +41,6 @@ An explanation of some terminology and conventions is in order. 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. - For backward compatibility, years with less than 4 digits are treated - specially by :func:`asctime`, :func:`mktime`, and :func:`strftime` functions - that operate on a 9-tuple or :class:`struct_time` values. If year (the first - value in the 9-tuple) is specified with less than 4 digits, its interpretation - depends on the value of ``accept2dyear`` variable. - - If ``accept2dyear`` is true (default), a backward compatibility behavior is - invoked as follows: - - - for 2-digit year, century is guessed according to POSIX rules for - ``%y`` strptime format. A deprecation warning is issued when century - information is guessed in this way. - - - for 3-digit or negative year, a :exc:`ValueError` exception is raised. - - If ``accept2dyear`` is false (set by the program or as a result of a - non-empty value assigned to ``PYTHONY2K`` environment variable) all year - values are interpreted as given. - .. index:: single: UTC single: Coordinated Universal Time @@ -117,24 +98,6 @@ An explanation of some terminology and conventions is in order. The module defines the following functions and data items: - -.. data:: accept2dyear - - Boolean value indicating whether two-digit year values will be - mapped to 1969--2068 range by :func:`asctime`, :func:`mktime`, and - :func:`strftime` functions. This is true by default, but will be - set to false if the environment variable :envvar:`PYTHONY2K` has - been set to a non-empty string. It may also be modified at run - time. - - .. deprecated:: 3.2 - Mapping of 2-digit year values by :func:`asctime`, - :func:`mktime`, and :func:`strftime` functions to 1969--2068 - range is deprecated. Programs that need to process 2-digit - years should use ``%y`` code available in :func:`strptime` - function or convert 2-digit year values to 4-digit themselves. - - .. data:: altzone The offset of the local DST timezone, in seconds west of UTC, if one is defined. @@ -152,7 +115,8 @@ The module defines the following functions and data items: .. note:: - Unlike the C function of the same name, there is no trailing newline. + Unlike the C function of the same name, :func:`asctime` does not add a + trailing newline. .. function:: clock() @@ -172,6 +136,121 @@ The module defines the following functions and data items: :c:func:`QueryPerformanceCounter`. The resolution is typically better than one microsecond. + .. deprecated:: 3.3 + The behaviour of this function depends on the platform: use + :func:`perf_counter` or :func:`process_time` instead, depending on your + requirements, to have a well defined behaviour. + + +.. function:: clock_getres(clk_id) + + Return the resolution (precision) of the specified clock *clk_id*. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. function:: clock_gettime(clk_id) + + Return the time of the specified clock *clk_id*. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. class:: clock_info + + Clock information object returned by :func:`get_clock_info`. + + .. attribute:: implementation + + The name of the underlying C function used to get the clock value. + + .. attribute:: monotonic + + ``True`` if the clock cannot go backward, ``False`` otherwise. + + .. attribute:: adjusted + + ``True`` if the clock can be adjusted (e.g. by a NTP daemon), ``False`` + otherwise. + + .. attribute:: resolution + + The resolution of the clock in seconds (:class:`float`). + + .. versionadded:: 3.3 + + +.. function:: clock_settime(clk_id, time) + + Set the time of the specified clock *clk_id*. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. data:: 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. + + Availability: Solaris. + + .. versionadded:: 3.3 + + +.. data:: CLOCK_MONOTONIC + + Clock that cannot be set and represents monotonic time since some unspecified + starting point. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. data:: CLOCK_MONOTONIC_RAW + + Similar to :data:`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. + + .. versionadded:: 3.3 + + +.. data:: CLOCK_PROCESS_CPUTIME_ID + + High-resolution per-process timer from the CPU. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. data:: CLOCK_REALTIME + + System-wide real-time clock. Setting this clock requires appropriate + privileges. + + Availability: Unix. + + .. versionadded:: 3.3 + + +.. data:: CLOCK_THREAD_CPUTIME_ID + + Thread-specific CPU-time clock. + + Availability: Unix. + + .. versionadded:: 3.3 + .. function:: ctime([secs]) @@ -186,6 +265,21 @@ The module defines the following functions and data items: Nonzero if a DST timezone is defined. +.. function:: get_clock_info(name) + + Get information on the specified clock as a :class:`clock_info` object. + Supported clock names and the corresponding functions to read their value + are: + + * ``'clock'``: :func:`time.clock` + * ``'monotonic'``: :func:`time.monotonic` + * ``'perf_counter'``: :func:`time.perf_counter` + * ``'process_time'``: :func:`time.process_time` + * ``'time'``: :func:`time.time` + + .. versionadded:: 3.3 + + .. function:: gmtime([secs]) Convert a time expressed in seconds since the epoch to a :class:`struct_time` in @@ -215,6 +309,48 @@ The module defines the following functions and data items: The earliest date for which it can generate a time is platform-dependent. +.. function:: 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, :func:`monotonic` detects + :c:func:`GetTickCount` integer overflow (32 bits, roll-over after 49.7 days). + It increases an internal epoch (reference time by) 2\ :sup:`32` each time + that an overflow is detected. The epoch is stored in the process-local state + and so the value of :func:`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, :func:`monotonic` is system-wide. + + Availability: Windows, Mac OS X, Linux, FreeBSD, OpenBSD, Solaris. + + .. versionadded:: 3.3 + + +.. function:: 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. + + .. versionadded:: 3.3 + + +.. function:: 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. + + .. versionadded:: 3.3 + + .. function:: sleep(secs) Suspend execution for the given number of seconds. The argument may be a @@ -308,7 +444,7 @@ The module defines the following functions and data items: | ``%y`` | Year without century as a decimal number | | | | [00,99]. | | +-----------+------------------------------------------------+-------+ - | ``%Y`` | Year with century as a decimal number. | \(4) | + | ``%Y`` | Year with century as a decimal number. | | | | | | +-----------+------------------------------------------------+-------+ | ``%Z`` | Time zone name (no characters if no time zone | | @@ -332,12 +468,6 @@ The module defines the following functions and data items: When used with the :func:`strptime` function, ``%U`` and ``%W`` are only used in calculations when the day of the week and the year are specified. - (4) - Produces different results depending on the value of - ``time.accept2dyear`` variable. See :ref:`Year 2000 (Y2K) - issues <time-y2kissues>` for details. - - Here is an example, a format for dates compatible with that specified in the :rfc:`2822` Internet email standard. [#]_ :: @@ -418,8 +548,7 @@ The module defines the following functions and data items: +-------+-------------------+---------------------------------+ Note that unlike the C structure, the month value is a range of [1, 12], not - [0, 11]. A year value will be handled as described under :ref:`Year 2000 - (Y2K) issues <time-y2kissues>` above. A ``-1`` argument as the daylight + [0, 11]. A ``-1`` argument as the daylight savings flag, passed to :func:`mktime` will usually result in the correct daylight savings state to be filled in. |