replace deprecated time.clock() by time.process_time()

[aqualogy]

With the release of Python 3.8 the function time.clock() has been removed, after having been deprecated since Python 3.3:
What’s New In Python 3.8

Calls to time.clock() should be replaced by calls to either time.perf_counter() or time.process_time(), depending on requirements.

I searched through the code of grass and replaced all occurences of time.clock() with time.process_time().

[wenzeslaus]

Do we need this to be Python 2 compatible? We won't be backporting it, so perhaps not. But also wrapping this would be easy, so perhaps worth it.

At this point, I don't know how to decide if time.perf_counter() would be more appropriate in some cases.

time.clock()

On Unix, return the current processor time as a floating point number expressed in seconds. The precision, and in fact the very definition of the meaning of “processor time”, depends on that of the C function of the same name.

On Windows, this function returns wall-clock seconds elapsed since the first call to this function, as a floating point number, based on the Win32 function QueryPerformanceCounter(). The resolution is typically better than one microsecond.

Deprecated since version 3.3, will be removed in version 3.8: The behaviour of this function depends on the platform: use perf_counter() or process_time() instead, depending on your requirements, to have a well defined behaviour.

time.perf_counter() → float

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.

New in version 3.3.

time.process_time() → float

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.

New in version 3.3.

[petrasovaa]

Thank you, I replaced this with #244, uses time.perf_counter(), although I am not entirely sure which one is better, it's used e.g. in timeit