High-precision clock in Python

Question

Is there a way to measure time with high-precision in Python --- more precise than one second   I doubt that there is a cross-platform way of doing that  I m interesting in high precision time on Unix  particularly Solaris running on a Sun SPARC machine   timeit seems to be capable of high-precision time measurement  but rather than measure how long a code snippet takes  I d like to directly access the time values

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I observed that the resolution of time time   is different between Windows 10 Professional and Education versions   On a Windows 10 Professional machine  the resolution is 1 ms   On a Windows 10 Education machine  the resolution is 16 ms   Fortunately  there s a tool that increases Python s time resolution in Windows  https   vvvv org contribution windows-system-timer-tool  With this tool  I was able to achieve 1 ms resolution regardless of Windows version  You will need to be keep it running while executing your Python codes

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def start self       sec arg   10 0     cptr   0     time start   time time       time init   time time       while True          cptr    1         time start   time time           time sleep   time init    sec arg   cptr   - time start               AND YOUR CODE                 t00   threading Thread name  thread request   target self send request  args               t00 start

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David s post was attempting to show what the clock resolution is on Windows  I was confused by his output  so I wrote some code that shows that time time   on my Windows 8 x64 laptop has a resolution of 1 msec     measure the smallest time delta by spinning until the time changes def measure        t0   time time       t1   t0     while t1    t0          t1   time time       return  t0  t1  t1-t0   samples    measure   for i in range 10    for s in samples      print s   Which outputs    1390455900 085  1390455900 086  0 0009999275207519531   1390455900 086  1390455900 087  0 0009999275207519531   1390455900 087  1390455900 088  0 0010001659393310547   1390455900 088  1390455900 089  0 0009999275207519531   1390455900 089  1390455900 09  0 0009999275207519531   1390455900 09  1390455900 091  0 0010001659393310547   1390455900 091  1390455900 092  0 0009999275207519531   1390455900 092  1390455900 093  0 0009999275207519531   1390455900 093  1390455900 094  0 0010001659393310547   1390455900 094  1390455900 095  0 0009999275207519531    And a way to do a 1000 sample average of the delta   reduce  lambda a b a b   measure   2  for i in range 1000    0 0    1000 0   Which output on two consecutive runs   0 001 0 0010009999275207519   So time time   on my Windows 8 x64 has a resolution of 1 msec   A similar run on time clock   returns a resolution of 0 4 microseconds    def measure clock        t0   time clock       t1   time clock       while t1    t0          t1   time clock       return  t0  t1  t1-t0   reduce  lambda a b a b   measure clock   2  for i in range 1000000     1000000 0   Returns   4 3571334791658954e-07   Which is  0 4e-06  An interesting thing about time clock   is that it returns the time since the method was first called  so if you wanted microsecond resolution wall time you could do something like this   class HighPrecisionWallTime        def   init   self            self  wall time 0   time time           self  clock 0   time clock        def sample self            dc   time clock  -self  clock 0         return self  wall time 0   dc    which would probably drift after a while  but you could correct this occasionally  for example dc  gt  3600 would correct it every hour

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Python tries hard to use the most precise time function for your platform to implement time time         Implement floattime   for various platforms     static double floattime void           There are three ways to get the time         1  gettimeofday   -- resolution in microseconds        2  ftime   -- resolution in milliseconds        3  time   -- resolution in seconds       In all cases the return value is a float in seconds        Since on some systems  e g  SCO ODT 3 0  gettimeofday   may       fail  so we fall back on ftime   or time          Note  clock resolution does not imply clock accuracy      ifdef HAVE GETTIMEOFDAY               struct timeval t   ifdef GETTIMEOFDAY NO TZ         if  gettimeofday  amp t     0              return  double t tv sec   t tv usec 0 000001   else     GETTIMEOFDAY NO TZ            if  gettimeofday  amp t   struct timezone   NULL     0              return  double t tv sec   t tv usec 0 000001   endif     GETTIMEOFDAY NO TZ            endif     HAVE GETTIMEOFDAY           if defined HAVE FTIME          struct timeb t          ftime  amp t           return  double t time    double t millitm    double 0 001   else     HAVE FTIME            time t secs          time  amp secs           return  double secs   endif     HAVE FTIME                from http   svn python org view python trunk Modules timemodule c revision 81756 amp view markup

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If Python 3 is an option  you have two choices    time perf counter which always use the most accurate clock on your platform  It does include time spent outside of the process  time process time which returns the CPU time  It does NOT include time spent outside of the process    The difference between the two can be shown with   from time import       process time      perf counter      sleep     print process time    sleep 1  print process time     print perf counter    sleep 1  print perf counter      Which outputs   0 03125 0 03125 2 560001310720671e-07 1 0005455362793145

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time clock   has 13 decimal points on Windows but only two on Linux  time time   has 17 decimals on Linux and 16 on Windows but the actual precision is different   I don t agree with the documentation that time clock   should be used for benchmarking on Unix Linux  It is not precise enough  so what timer to use depends on operating system   On Linux  the time resolution is high in time time      gt  gt  gt  time time    time time    1281384913 4374139  1281384913 4374161    On Windows  however the time function seems to use the last called number    gt  gt  gt  time time  -int time time     time time  -int time time     time time  -time time    0 9570000171661377  0 9570000171661377  0 0    Even if I write the calls on different lines in Windows it still returns the same value so the real precision is lower   So in serious measurements a platform check  import platform  platform system    has to be done in order to determine whether to use time clock   or time time      Tested on Windows 7 and Ubuntu 9 10 with python 2 6 and 3 1

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On the same win10 OS system using  quot two distinct method approaches quot  there appears to be an approximate  quot 500 ns quot  time difference  If you care about nanosecond precision check my code below  The modifications of the code is based on code from user cod3monk3y and Kevin S  OS  python 3 7 3  default  date  time   MSC v 1915 64 bit  AMD64   def measure1 mean       for i in range 1  my range 1           x   time time                    td   x- samples1 i-1  2          if i-1    0              td   0         td   f  td  6f           samples1 append  i  td  x           mean    float td          print  mean          sys stdout flush           time sleep 0 001           mean   mean my range          return mean  def measure2 nr       t0   time time       t1   t0     while t1    t0          t1   time time       td   t1-t0     td   f  td  6f       return  nr  td  t1  t0   samples1     0  0  0   my range   10 mean1      0 0 mean2      0 0  mean1   measure1 mean1   for i in samples1  print  i   print       n n    samples2    measure2 i  for i in range 11    for s in samples2       print f time delta   s  4f  seconds       mean2    float s 1       print  s       mean2   mean2 my range  print    nMean1     f  mean1  6f    print   Mean2     f  mean2  6f     The measure1 results  nr  td  t0  0  0  0   1   0 000000   1562929696 617988   2   0 002000   1562929696 6199884   3   0 001001   1562929696 620989   4   0 001001   1562929696 62199   5   0 001001   1562929696 6229906   6   0 001001   1562929696 6239917   7   0 001001   1562929696 6249924   8   0 001000   1562929696 6259928   9   0 001001   1562929696 6269937   10   0 001001   1562929696 6279945       The measure2 results  nr  td   t1  t0  0   0 000500   1562929696 6294951  1562929696 6289947   1   0 000501   1562929696 6299958  1562929696 6294951   2   0 000500   1562929696 6304958  1562929696 6299958   3   0 000500   1562929696 6309962  1562929696 6304958   4   0 000500   1562929696 6314962  1562929696 6309962   5   0 000500   1562929696 6319966  1562929696 6314962   6   0 000500   1562929696 632497  1562929696 6319966   7   0 000500   1562929696 6329975  1562929696 632497   8   0 000500   1562929696 633498  1562929696 6329975   9   0 000500   1562929696 6339984  1562929696 633498   10   0 000500   1562929696 6344984  1562929696 6339984   End result   Mean1   0 001001      measure1 function  Mean2   0 000550      measure2 function

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Python 3 7 introduces 6 new time functions with nanosecond resolution  for example instead of time time   you can use time time ns   to avoid floating point imprecision issues   import time print time time      1522915698 3436284 print time time ns      1522915698343660458   These 6 functions are described in PEP 564      time clock gettime ns clock id       time clock settime ns clock id  time int       time monotonic ns        time perf counter ns        time process time ns        time time ns        These functions are similar to the version without the  ns suffix  but   return a number of nanoseconds as a Python int

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You can also use time clock   It counts the time used by the process on Unix and time since the first call to it on Windows  It s more precise than time time     It s the usually used function to measure performance   Just call   import time t    time clock    Your code here print  Time in function   time clock   - t    EDITED  Ups  I miss the question as you want to know exactly the time  not the time spent

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The comment left by tiho on Mar 27  14 at 17 21 deserves to be its own answer      In order to avoid platform-specific code  use timeit default timer

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For those stuck on windows  version    server 2012 or win 8 and python 2 7   import ctypes  class FILETIME ctypes Structure        fields       dwLowDateTime   ctypes c uint                     dwHighDateTime   ctypes c uint    def time           Accurate version of time time   for windows  return UTC time in term of seconds since 01 01 1601         file time   FILETIME       ctypes windll kernel32 GetSystemTimePreciseAsFileTime ctypes byref file time       return  file time dwLowDateTime    file time dwHighDateTime  lt  lt  32     1 0e7   GetSystemTimePreciseAsFileTime function

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The standard time time   function provides sub-second precision  though that precision varies by platform  For Linux and Mac precision is  - 1 microsecond or 0 001 milliseconds  Python on Windows uses  - 16 milliseconds precision due to clock implementation problems due to process interrupts  The timeit module can provide higher resolution if you re measuring execution time    gt  gt  gt  import time  gt  gt  gt  time time           return seconds from epoch 1261367718 971009         Python 3 7 introduces new functions to the time module that provide higher resolution    gt  gt  gt  import time  gt  gt  gt  time time ns   1530228533161016309  gt  gt  gt  time time ns      10    9    convert to floating-point seconds 1530228544 0792289

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The original question specifically asked for Unix but multiple answers have touched on Windows  and as a result there is misleading information on windows   The default timer resolution on windows is 15 6ms you can verify here   Using a slightly modified script from cod3monk3y I can show that windows timer resolution is  15milliseconds by default   I m using a tool available here to modify the resolution   Script   import time    measure the smallest time delta by spinning until the time changes def measure        t0   time time       t1   t0     while t1    t0          t1   time time       return t1-t0  samples    measure   for i in range 30    for s in samples      print f time delta   s  4f  seconds          These results were gathered on windows 10 pro 64-bit running python 3 7 64-bit

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Here is a python 3 solution for Windows building upon the answer posted above by CyberSnoopy  using GetSystemTimePreciseAsFileTime   We borrow some code from jfs  Python datetime utcnow   returning incorrect datetime  and get a precise timestamp  Unix time  in microseconds     python3 import ctypes wintypes  def utcnow microseconds        system time   ctypes wintypes FILETIME        system call used by time time        ctypes windll kernel32 GetSystemTimeAsFileTime ctypes byref system time        getting high precision      ctypes windll kernel32 GetSystemTimePreciseAsFileTime ctypes byref system time       large    system time dwHighDateTime  lt  lt  32    system time dwLowDateTime     return large    10 - 11644473600000000  for ii in range 5       print utcnow microseconds   1e-6    References https   docs microsoft com en-us windows win32 sysinfo time-functions https   docs microsoft com en-us windows win32 api sysinfoapi nf-sysinfoapi-getsystemtimepreciseasfiletime https   support microsoft com en-us help 167296 how-to-convert-a-unix-time-t-to-a-win32-filetime-or-systemtime

[python] High-precision clock in Python

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