python time.time() differences in python 2 vs 3

Question

I am wondering why python 2.7 uses gettimeofday() when running time.time() but yet in python 3.4 it does not?

It appears when running strace that it may be querying /etc/localtime

Is there any problem with the different implementation? The Python 3 time module was overhauled when the various new clock types were added. — Martijn Pieters
– Martijn Pieters, Commented Jul 22, 2016 at 19:17
Yes using the virtual time kernel github.com/littlepretty/VirtualTimeKernel Which relies on GToD — channon
– channon, Commented Jul 22, 2016 at 19:19
Also the docs are misleading suggesting that if available it should use GToD docs.python.org/3.4/library/time.html — channon
– channon, Commented Jul 22, 2016 at 19:23
The documentation is not lying; perhaps you need to build Python directly on your system instead? See the pygettimeofday() function specifically. — Martijn Pieters
– Martijn Pieters, Commented Jul 22, 2016 at 19:45

Martijn Pieters · Accepted Answer · 2016-07-22 19:56:15Z

2

Python 3 will use gettimeofday() when your system has been detected to support this at compile time. However, on POSIX systems it'll only use that if clock_gettime(CLOCK_REALTIME) is not available instead; according to the POSIX 2008 standard the latter is preferred as gettimeofday() is considered obsolete.

At runtime, you can query what Python thought your system could support at compile time by using the time.get_clock_info() function, which returns a namedtuple instance with a implementation field:

implementation: The name of the underlying C function used to get the clock value

On my OSX 10.11 system, for the 'time' clock, that produces gettimeofday():

>>> time.get_clock_info('time').implementation
'gettimeofday()'

You can read through the pygettimeofday() C implementation to see what implementations may be used; on Windows GetSystemTimeAsFileTime() is used for example.

edited Jul 22, 2016 at 19:56

answered Jul 22, 2016 at 19:50

Martijn Pieters

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3 Comments

channon Over a year ago

Thanks for the info. I will try to force it to use GToD as its clocking mechanism.

Martijn Pieters Over a year ago

@channon: not sure why you'd need to as I see VirtualTimeKernel supports clock_gettime().

channon Over a year ago

because the virtual time only effects GToD it is in the code for that function

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