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

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

I've a python script which works just as it should but I need to write the time for the execution. 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 >= '2010' and MyCount < '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 it the time it takes the execution of the query and written to the file "results_update.txt". The purpose is to test an update statement for my database with different indexes and tuning mechanisms.

Answer by joaquin for How can I time a code segment for testing performance with Pythons timeit?

you can use time.time ot 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 straighforward.

time.time() (in windows and linux) and time.clock(in linux) have not enough resolution 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 must be prefered to time.time().

Answer by Alex Martelli for How can I time a code segment for testing performance with Pythons timeit?

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;-).

Answer by munk for How can I time a code segment for testing performance with Pythons timeit?

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  

Answer by Abhijit Mamarde for How can I time a code segment for testing performance with Pythons timeit?

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 available as github gist here.

Hope it will help you and others.

Answer by Martijn Pieters for How can I time a code segment for testing performance with Pythons timeit?

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.

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