Thanks to my latest change on time.perf_counter(), all Python 3.7 clocks now use nanoseconds as integer internally. It became possible to propose again my old idea of getting time as nanoseconds at Python level and so I wrote a new PEP 564 "Add new time functions with nanosecond resolution". While the PEP was discussed, I also deprecated time.clock() and removed os.stat_float_times().

Old clock


Since I wrote the PEP 418 "Add monotonic time, performance counter, and process time functions" in 2012, I dislike time.clock(). This clock is not portable: on Windows it mesures wall-clock, whereas it measures CPU time on Unix. Extract of time.clock() documentation:

Deprecated since version 3.3: 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.

My PEP 418 deprecated time.clock() in the documentation. In bpo-31803, I modified time.clock() and time.get_clock_info('clock') to also emit a DeprecationWarning warning. I replaced time.clock() with time.perf_counter() in tests and demos. I also removed hasattr(time, 'monotonic') in test_time since time.monotonic() is always available since Python 3.5.


The os.stat_float_times() function was introduced in Python 2.3 to get file modification times with sub-second resolution (commit f607bdaa), the default was still to get time as seconds (integer). The function was introduced to get a smooth transition to time as floating point number, to keep the backward compatibility with Python 2.2.

os.stat() was modified to return time as float by default in Python 2.5 (commit fe33d0ba). Python 2.5 was released 11 years ago, I consider that people had enough time to migrate their code to float time :-) I modified os.stat_float_times() in Python 3.1 to emit a DeprecationWarning warning (commit 034d0aa2 of bpo-14711).

Finally, I removed os.stat_float_times() in Python 3.7: bpo-31827.

Serhiy Storchaka proposed to also remove last three items from os.stat_result. For example, stat_result[stat.ST_MTIME] could be replaced with stat_result.st_time. But I tried to remove these items and it broke the logging module, so I decided to leave it unchanged.

PEP 564: time.time_ns()

Six years ago (2012), I wrote the PEP 410 "Use decimal.Decimal type for timestamps" which proposes a large and complex change in all Python functions returning time to support nanosecond resolution using the decimal.Decimal type. The PEP was rejected for different reasons.

Since all clock now use nanoseconds internally in Python 3.7, I proposed a new PEP 564 "Add new time functions with nanosecond resolution". Abstract:

Add six new "nanosecond" variants of existing functions to the time module: clock_gettime_ns(), clock_settime_ns(), monotonic_ns(), perf_counter_ns(), process_time_ns() and time_ns(). While similar to the existing functions without the _ns suffix, they provide nanosecond resolution: they return a number of nanoseconds as a Python int.

The time.time_ns() resolution is 3 times better than the time.time() resolution on Linux and Windows.

People were now convinced by the need for nanosecond resolution, so I added an "Issues caused by precision loss" section with 2 examples:

  • Example 1: measure time delta in long-running process
  • Example 2: compare times with different resolution

As for my previous PEP 410, many people proposed many alternatives recorded in the PEP: sub-nanosecond resolution, modifying time.time() result type, different types, different API, a new module, etc.

Hopefully for me, Guido van Rossum quickly approved my PEP for Python 3.7!

Implementaton of the PEP 564

I implemented my PEP 564 in bpo-31784 with the commit c29b585f. I added 6 new time functions:

  • time.clock_gettime_ns()
  • time.clock_settime_ns()
  • time.monotonic_ns()
  • time.perf_counter_ns()
  • time.process_time_ns()
  • time.time_ns()


$ python3.7
Python 3.7.0b2+ (heads/3.7:31e2b76f7b, Mar  6 2018, 15:31:29)
[GCC 7.2.1 20170915 (Red Hat 7.2.1-2)] on linux
>>> import time
>>> time.time()
>>> time.time_ns()

I also added tests on os.times() in test_os, previously the function wasn't tested at all!


I added 6 new functions to get time with a nanosecond resolution like time.time_ns() with my approved PEP 564. I also modified time.clock() to emit a DeprecationWarning and I removed the legacy os.stat_float_times() function.