diff --git a/Doc/library/time.rst b/Doc/library/time.rst index 6ef02b74031..ef0e69a5e8c 100644 --- a/Doc/library/time.rst +++ b/Doc/library/time.rst @@ -17,11 +17,23 @@ semantics of these functions varies among platforms. An explanation of some terminology and conventions is in order. +.. _epoch: + .. index:: single: epoch -* The :dfn:`epoch` is the point where the time starts. On January 1st of that - year, at 0 hours, the "time since the epoch" is zero. For Unix, the epoch is - 1970. To find out what the epoch is, look at ``gmtime(0)``. +* The :dfn:`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)``. + +.. _leap seconds: https://en.wikipedia.org/wiki/Leap_second + +.. index:: seconds since the epoch + +* The term :dfn:`seconds since the epoch` refers to the total number + of elapsed seconds since the epoch, typically excluding + `leap seconds`_. Leap seconds are excluded from this total on all + POSIX-compliant platforms. .. index:: single: Year 2038 @@ -467,7 +479,7 @@ The module defines the following functions and data items: (2) The range really is ``0`` to ``61``; value ``60`` is valid in - timestamps representing leap seconds and value ``61`` is supported + timestamps representing `leap seconds`_ and value ``61`` is supported for historical reasons. (3) @@ -572,12 +584,28 @@ The module defines the following functions and data items: .. function:: time() - Return the time in seconds since the epoch as a floating point number. + Return the time in seconds since the epoch_ as a floating point + number. The specific date of the epoch and the handling of + `leap seconds`_ 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. + lower value than a previous call if the system clock has been set back + between the two calls. + + The number returned by :func:`.time` may be converted into a more common + time format (i.e. year, month, day, hour, etc...) in UTC by passing it to + :func:`gmtime` function or in local time by passing it to the + :func:`localtime` function. In both cases a + :class:`struct_time` object is returned, from which the components + of the calendar date may be accessed as attributes. .. data:: timezone