mirror of
https://gitlab.com/kicad/code/kicad.git
synced 2024-11-24 23:25:02 +00:00
82 lines
3.8 KiB
ReStructuredText
82 lines
3.8 KiB
ReStructuredText
Chrono
|
|
======
|
|
|
|
When including the additional header file :file:`pybind11/chrono.h` conversions
|
|
from C++11 chrono datatypes to python datetime objects are automatically enabled.
|
|
This header also enables conversions of python floats (often from sources such
|
|
as ``time.monotonic()``, ``time.perf_counter()`` and ``time.process_time()``)
|
|
into durations.
|
|
|
|
An overview of clocks in C++11
|
|
------------------------------
|
|
|
|
A point of confusion when using these conversions is the differences between
|
|
clocks provided in C++11. There are three clock types defined by the C++11
|
|
standard and users can define their own if needed. Each of these clocks have
|
|
different properties and when converting to and from python will give different
|
|
results.
|
|
|
|
The first clock defined by the standard is ``std::chrono::system_clock``. This
|
|
clock measures the current date and time. However, this clock changes with to
|
|
updates to the operating system time. For example, if your time is synchronised
|
|
with a time server this clock will change. This makes this clock a poor choice
|
|
for timing purposes but good for measuring the wall time.
|
|
|
|
The second clock defined in the standard is ``std::chrono::steady_clock``.
|
|
This clock ticks at a steady rate and is never adjusted. This makes it excellent
|
|
for timing purposes, however the value in this clock does not correspond to the
|
|
current date and time. Often this clock will be the amount of time your system
|
|
has been on, although it does not have to be. This clock will never be the same
|
|
clock as the system clock as the system clock can change but steady clocks
|
|
cannot.
|
|
|
|
The third clock defined in the standard is ``std::chrono::high_resolution_clock``.
|
|
This clock is the clock that has the highest resolution out of the clocks in the
|
|
system. It is normally a typedef to either the system clock or the steady clock
|
|
but can be its own independent clock. This is important as when using these
|
|
conversions as the types you get in python for this clock might be different
|
|
depending on the system.
|
|
If it is a typedef of the system clock, python will get datetime objects, but if
|
|
it is a different clock they will be timedelta objects.
|
|
|
|
Provided conversions
|
|
--------------------
|
|
|
|
.. rubric:: C++ to Python
|
|
|
|
- ``std::chrono::system_clock::time_point`` → ``datetime.datetime``
|
|
System clock times are converted to python datetime instances. They are
|
|
in the local timezone, but do not have any timezone information attached
|
|
to them (they are naive datetime objects).
|
|
|
|
- ``std::chrono::duration`` → ``datetime.timedelta``
|
|
Durations are converted to timedeltas, any precision in the duration
|
|
greater than microseconds is lost by rounding towards zero.
|
|
|
|
- ``std::chrono::[other_clocks]::time_point`` → ``datetime.timedelta``
|
|
Any clock time that is not the system clock is converted to a time delta.
|
|
This timedelta measures the time from the clocks epoch to now.
|
|
|
|
.. rubric:: Python to C++
|
|
|
|
- ``datetime.datetime`` or ``datetime.date`` or ``datetime.time`` → ``std::chrono::system_clock::time_point``
|
|
Date/time objects are converted into system clock timepoints. Any
|
|
timezone information is ignored and the type is treated as a naive
|
|
object.
|
|
|
|
- ``datetime.timedelta`` → ``std::chrono::duration``
|
|
Time delta are converted into durations with microsecond precision.
|
|
|
|
- ``datetime.timedelta`` → ``std::chrono::[other_clocks]::time_point``
|
|
Time deltas that are converted into clock timepoints are treated as
|
|
the amount of time from the start of the clocks epoch.
|
|
|
|
- ``float`` → ``std::chrono::duration``
|
|
Floats that are passed to C++ as durations be interpreted as a number of
|
|
seconds. These will be converted to the duration using ``duration_cast``
|
|
from the float.
|
|
|
|
- ``float`` → ``std::chrono::[other_clocks]::time_point``
|
|
Floats that are passed to C++ as time points will be interpreted as the
|
|
number of seconds from the start of the clocks epoch.
|