How can I time a code segment for testing performance with Pythons timeit

Question

I ve a python script which works just as it should  but I need to write the execution time  I ve googled that I should use timeit but I can t seem to get it to work   My Python script looks like this   import sys import getopt import timeit import random import os import re import ibm db import time from string import maketrans myfile   open  results update txt    a    for r in range 100       rannumber   random randint 0  100       update    update TABLE set val    i where MyCount  gt    2010  and MyCount  lt   2012  and number    250     rannumber      print rannumber      conn   ibm db pconnect  dsn myDB   usrname   secretPWD    for r in range 5       print  Run  s n    r             ibm db execute query stmt   query stmt   ibm db prepare conn  update   myfile close   ibm db close conn    What I need is the time it takes to execute the query and write it to the file results update txt  The purpose is to test an update statement for my database with different indexes and tuning mechanisms

User · Answer

Here s a simple wrapper for steven s answer  This function doesn t do repeated runs averaging  just saves you from having to repeat the timing code everywhere        function which prints the wall time it takes to execute the given command    def time func func   args     args can take 0 or more    import time   start time   time time     func  args    end time   time time     print  it took this long to run      format end time-start time

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The testing suite doesn t make an attempt at using the imported timeit so it s hard to tell what the intent was  Nonetheless  this is a canonical answer so a complete example of timeit seems in order  elaborating on Martijn s answer  The docs for timeit offer many examples and flags worth checking out  The basic usage on the command line is    python -mtimeit  quot all True for   in range 1000   quot  2000 loops  best of 5  161 usec per loop   python -mtimeit  quot all  True for   in range 1000    quot  2000 loops  best of 5  116 usec per loop  Run with -h to see all options  Python MOTW has a great section on timeit that shows how to run modules via import and multiline code strings from the command line  In script form  I typically use it like this  import argparse import copy import dis import inspect import random import sys import timeit  def test slice L       L     def test copy L       L copy    def test deepcopy L       copy deepcopy L   if   name       quot   main   quot       parser   argparse ArgumentParser       parser add argument  quot --n quot   type int  default 10    5      parser add argument  quot --trials quot   type int  default 100      parser add argument  quot --dis quot   action  quot store true quot       args   parser parse args       n   args n     trials   args trials     namespace   dict L   random sample range n   k n       funcs to test    x for x in locals   values                         if callable x  and x   module        name        print f quot   -    30  nn    n    trials  trials n  -    30  n quot        for func in funcs to test          fname   func   name           fargs    quot    quot  join inspect signature func  parameters          stmt   f quot  fname   fargs   quot          setup   f quot from   main   import  fname  quot          time   timeit timeit stmt  setup  number trials  globals namespace          print inspect getsource globals   get fname             if args dis              dis dis globals   get fname            print f quot time  s    gt   time  n  -    30  n quot    You can pretty easily drop in the functions and arguments you need  Use caution when using impure functions and take care of state  Sample output    python benchmark py --n 10000 ------------------------------ n   10000  100 trials ------------------------------  def test slice L       L     time  s    gt  0 015502399999999972 ------------------------------  def test copy L       L copy    time  s    gt  0 01651419999999998 ------------------------------  def test deepcopy L       copy deepcopy L   time  s    gt  2 136012 ------------------------------

User · Answer

Here is an example of how to time a function using timeit  import timeit  def time this n       return  str i  for i in range n    timeit timeit lambda  time this n 5000   number 1000   This will return the time in seconds it took to execute the time this   function 1000 times

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Focus on one specific thing  Disk I O is slow  so I d take that out of the test if all you are going to tweak is the database query   And if you need to time your database execution  look for database tools instead  like asking for the query plan  and note that performance varies not only with the exact query and what indexes you have  but also with the data load  how much data you have stored    That said  you can simply put your code in a function and run that function with timeit timeit     def function to repeat               duration   timeit timeit function to repeat  number 1000    This would disable the garbage collection  repeatedly call the function to repeat   function  and time the total duration of those calls using timeit default timer    which is the most accurate available clock for your specific platform   You should move setup code out of the repeated function  for example  you should connect to the database first  then time only the queries  Use the setup argument to either import or create those dependencies  and pass them into your function   def function to repeat var1  var2              duration   timeit timeit       function to repeat var1  var2         from   main   import function to repeat  var1  var2        number 1000    would grab the globals function to repeat  var1 and var2 from your script and pass those to the function each repetition

User · Answer

Quite apart from the timing  this code you show is simply incorrect  you execute 100 connections  completely ignoring all but the last one   and then when you do the first execute call you pass it a local variable query stmt which you only initialize after the execute call   First  make your code correct  without worrying about timing yet  i e  a function that makes or receives a connection and performs 100 or 500 or whatever number of updates on that connection  then closes the connection  Once you have your code working correctly is the correct point at which to think about using timeit on it   Specifically  if the function you want to time is a parameter-less one called foobar you can use timeit timeit  2 6 or later -- it s more complicated in 2 5 and before    timeit timeit  foobar     number 1000    You d better specify the number of runs because the default  a million  may be high for your use case  leading to spending a lot of time in this code -

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If you are profiling your code and can use IPython  it has the magic function  timeit     timeit operates on cells   In  2    timeit cos 3 14  10000000 loops  best of 3  160 ns per loop  In  3     timeit         cos 3 14          x   2   3          10000000 loops  best of 3  196 ns per loop

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You can use time time   or time clock   before and after the block you want to time   import time  t0   time time   code block t1   time time    total   t1-t0   This method is not as exact as timeit  it does not average several runs  but it is straightforward    time time    in Windows and Linux  and time clock    in Linux  are not precise enough for fast functions  you get total   0   In this case or if you want to average the time elapsed by several runs  you have to manually call the function multiple times  As I think you already do in you example code and timeit does automatically when you set its number argument   import time  def myfast       code  n   10000 t0   time time   for i in range n   myfast   t1   time time    total n   t1-t0   In Windows  as Corey stated in the comment  time clock   has much higher precision  microsecond instead of second  and is preferred over time time

User · Answer

Another simple timeit example  def your function to test         do some stuff     time to run 100 times   timeit timeit lambda  your function to test  number 100

User · Answer

I see the question has already been answered  but still want to add my 2 cents for the same   I have also faced similar scenario in which I have to test the execution times for several approaches and hence written a small script  which calls timeit on all functions written in it   The script is also available as github gist here   Hope it will help you and others   from random import random import types  def list without comprehension        l          for i in xrange 1000           l append int random   100   100       return l  def list with comprehension          1K random numbers between 0 to 100     l    int random   100   100  for   in xrange 1000       return l     operations on list without comprehension def sort list without comprehension        list without comprehension   sort    def reverse sort list without comprehension        list without comprehension   sort reverse True   def sorted list without comprehension        sorted list without comprehension        operations on list with comprehension def sort list with comprehension        list with comprehension   sort    def reverse sort list with comprehension        list with comprehension   sort reverse True   def sorted list with comprehension        sorted list with comprehension      def main        objs   globals       funcs          f   open  timeit demo sh    w         for objname in objs          if objname     main  and type objs objname      types FunctionType              funcs append objname      funcs sort       for func in funcs          f write    echo  Timing    funcname s  python -m timeit  import timeit demo  timeit demo   funcname s     n n echo  ------------------------------------------------------------        dict                  funcname   func                                       f close    if   name         main         main        from os import system       Works only for  nix platforms     system   bin bash timeit demo sh         un-comment below for windows      system  cmd timeit demo sh

[python] How can I time a code segment for testing performance with Pythons timeit?

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