windows - Python resolution of datetime.now() -

from datetime import datetime import time in range(1000):     curr_time  = datetime.now()     print(curr_time)     time.sleep(0.0001) 

i testing resolution of datetime.now(). since supposes output in microsecond, expected each print different.

however, that.

... 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.212073 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 2015-07-10 22:38:47.213074 ... 

why happen? there way can accurate timestamp down microsecond? don't need microseconds, nice 0.1ms resolution.

=== update ====

i compared using time.perf_counter() , adding starting datetime datetime import datetime, timedelta import time

datetime0 = datetime.now() t0 = time.perf_counter() in range(1000):     print('datetime.now(): ', datetime.now())     print('time.perf_counter(): ', datetime0 + timedelta(0, time.perf_counter()-t0))     print('\n')      time.sleep(0.000001) 

i not sure how 'accurate' is, resolution @ least higher.... doesn't seems matter computer cannot print @ speed high. purpose, need different timestamps distinguish different entries, enough me.

... datetime.now():  2015-07-10 23:24:18.010377 time.perf_counter():  2015-07-10 23:24:18.010352   datetime.now():  2015-07-10 23:24:18.010377 time.perf_counter():  2015-07-10 23:24:18.010545   datetime.now():  2015-07-10 23:24:18.010377 time.perf_counter():  2015-07-10 23:24:18.010745   datetime.now():  2015-07-10 23:24:18.011377 time.perf_counter():  2015-07-10 23:24:18.010961   datetime.now():  2015-07-10 23:24:18.011377 time.perf_counter():  2015-07-10 23:24:18.011155   datetime.now():  2015-07-10 23:24:18.011377 time.perf_counter():  2015-07-10 23:24:18.011369   datetime.now():  2015-07-10 23:24:18.011377 time.perf_counter():  2015-07-10 23:24:18.011596   datetime.now():  2015-07-10 23:24:18.012379 time.perf_counter():  2015-07-10 23:24:18.011829   datetime.now():  2015-07-10 23:24:18.012379 time.perf_counter():  2015-07-10 23:24:18.012026   datetime.now():  2015-07-10 23:24:18.012379 time.perf_counter():  2015-07-10 23:24:18.012232   datetime.now():  2015-07-10 23:24:18.012379 time.perf_counter():  2015-07-10 23:24:18.012424   datetime.now():  2015-07-10 23:24:18.012379 time.perf_counter():  2015-07-10 23:24:18.012619   datetime.now():  2015-07-10 23:24:18.013380 time.perf_counter():  2015-07-10 23:24:18.012844   datetime.now():  2015-07-10 23:24:18.013380 time.perf_counter():  2015-07-10 23:24:18.013044   datetime.now():  2015-07-10 23:24:18.013380 time.perf_counter():  2015-07-10 23:24:18.013242   datetime.now():  2015-07-10 23:24:18.013380 time.perf_counter():  2015-07-10 23:24:18.013437   datetime.now():  2015-07-10 23:24:18.013380 time.perf_counter():  2015-07-10 23:24:18.013638   datetime.now():  2015-07-10 23:24:18.014379 time.perf_counter():  2015-07-10 23:24:18.013903   datetime.now():  2015-07-10 23:24:18.014379 time.perf_counter():  2015-07-10 23:24:18.014125   datetime.now():  2015-07-10 23:24:18.014379 time.perf_counter():  2015-07-10 23:24:18.014328   datetime.now():  2015-07-10 23:24:18.014379 time.perf_counter():  2015-07-10 23:24:18.014526   datetime.now():  2015-07-10 23:24:18.014379 time.perf_counter():  2015-07-10 23:24:18.014721   datetime.now():  2015-07-10 23:24:18.015381 time.perf_counter():  2015-07-10 23:24:18.014919  ... 

this may limitation of time.sleep on system, rather datetime.now()... or possibly both. what os , version , distribution of python running on?

your system may not offer "subsecond precision" mentioned in time.sleep docs:

sleep(...)     sleep(seconds)      delay execution given number of seconds.  argument may     floating point number subsecond precision. 

on linux 3.x on amd64 cpython 2.7, pretty close 0.0001 time steps intended:

2015-07-10 19:58:24.353711 2015-07-10 19:58:24.353879 2015-07-10 19:58:24.354052 2015-07-10 19:58:24.354227 2015-07-10 19:58:24.354401 2015-07-10 19:58:24.354577 2015-07-10 19:58:24.354757 2015-07-10 19:58:24.354938