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Python 3.3 has 3 functions to get time:
 - time.clock()
 - time.steady()
 - time.time()
Antoine Pitrou suggested to deprecated time.clock() in msg120149 (issue #10278).
"The problem is time.clock(), since it does two wildly different things
depending on the OS. I would suggest to deprecate time.clock() at the same time as we add time.wallclock(). For the Unix-specific definition of time.clock(), there is already os.times() (which gives even richer information)."
(time.wallclock was the old name of time.steady)

STINNER Victor wrote:
> 
> New submission from STINNER Victor <victor.stinner@gmail.com>:
> 
> Python 3.3 has 3 functions to get time:
> 
> - time.clock()
> - time.steady()
> - time.time()
> 
> Antoine Pitrou suggested to deprecated time.clock() in msg120149 (issue #10278).
> 
> "The problem is time.clock(), since it does two wildly different things
> depending on the OS. I would suggest to deprecate time.clock() at the same time as we add time.wallclock(). For the Unix-specific definition of time.clock(), there is already os.times() (which gives even richer information)."
> 
> (time.wallclock was the old name of time.steady)
Strong -1 on this idea.
time.clock() has been in use for ages in many many scripts. We don't
want to carelessly break all those.

> time.clock() has been in use for ages in many many scripts.
> We don't want to carelessly break all those.
I don't want to remove the function, just mark it as deprecated to
avoid confusion. It will only be removed from the next major Python.

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@gmail.com> added the comment:
> 
>> time.clock() has been in use for ages in many many scripts.
>> We don't want to carelessly break all those.
> 
> I don't want to remove the function, just mark it as deprecated to
> avoid confusion. It will only be removed from the next major Python.
Why ? There's no other single function providing the same functionality,
so it's not even a candidate for deprecation.
Similar functionality is available via several different functions,
but that's true for a lot functions in th stdlib.

> There's no other single function providing the same functionality
time.clock() is not portable: it is a different clock depending on the OS. To write portable code, you have to use the right function:
 - time.time()
 - time.steady()
 - os.times(), resource.getrusage()
On Windows, time.clock() should be replaced by time.steady(). On UNIX, time.clock() can be replaced with "usage=os.times(); usage[0]+usage[1]" for example.
Which kind of use case is not covered by these functions?

STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@gmail.com> added the comment:
> 
>> There's no other single function providing the same functionality
> 
> time.clock() is not portable: it is a different clock depending on the OS. To write portable code, you have to use the right function:
> 
> - time.time()
> - time.steady()
> - os.times(), resource.getrusage()
time.clock() does exactly what the docs say: you get access to
a CPU timer. It's normal that CPU timers work differently on
different OSes.
> On Windows, time.clock() should be replaced by time.steady().
What for ? time.clock() uses the same timer as time.steady() on Windows,
AFAICT, so all you change is the name of the function.
> On UNIX, time.clock() can be replaced with "usage=os.times(); usage[0]+usage[1]" for example.
And what's the advantage of that over using time.clock() directly ?

I misunderstood the time.clock() function. It counts the CPU time while the process is active, whereas a monotonic clock counts elapsed time even during a sleep. time.clock() and time.monotonic() are different clocks for different purposes.
I wrote the PEP 418 which contains a list of all available OS clocks. It lists monotonic clocks, but also "process time" and "thread time" clocks. And it has a "Deferred API: time.perf_counter()" section.
Something can be done to provide portable functions to get the user and system times. See for example Tools/pybench/systimes.py written by Marc-Andre Lemburg.
Python 3.3 gives access to clock_gettime(CLOCK_PROCESS_CPUTIME_ID) and clock_gettime(CLOCK_THREAD_CPUTIME_ID).

> Something can be done to provide portable functions to get
> the user and system times.
Lib/profile.py tests also various functions to choose the best one in Profile constructor.

New changeset 314c3faea2fb by Victor Stinner in branch 'default':
Close #14309: Deprecate time.clock()
http://hg.python.org/cpython/rev/314c3faea2fb 

The PEP 418 has been accepted: read it to understand why time.clock() is now deprecated.