How to use timeit module


Question

I understand the concept of what timeit does but I am not sure how to implement it in my code.

How can I compare two functions, say insertion_sort and tim_sort, with timeit?

1
311
7/1/2016 12:22:13 PM

Accepted Answer

The way timeit works is to run setup code once and then make repeated calls to a series of statements. So, if you want to test sorting, some care is required so that one pass at an in-place sort doesn't affect the next pass with already sorted data (that, of course, would make the Timsort really shine because it performs best when the data already partially ordered).

Here is an example of how to set up a test for sorting:

>>> import timeit

>>> setup = '''
import random

random.seed('slartibartfast')
s = [random.random() for i in range(1000)]
timsort = list.sort
'''

>>> print min(timeit.Timer('a=s[:]; timsort(a)', setup=setup).repeat(7, 1000))
0.334147930145

Note that the series of statements makes a fresh copy of the unsorted data on every pass.

Also, note the timing technique of running the measurement suite seven times and keeping only the best time -- this can really help reduce measurement distortions due to other processes running on your system.

Those are my tips for using timeit correctly. Hope this helps :-)

250
2/22/2015 7:55:57 PM

If you want to use timeit in an interactive Python session, there are two convenient options:

  1. Use the IPython shell. It features the convenient %timeit special function:

    In [1]: def f(x):
       ...:     return x*x
       ...: 
    
    In [2]: %timeit for x in range(100): f(x)
    100000 loops, best of 3: 20.3 us per loop
    
  2. In a standard Python interpreter, you can access functions and other names you defined earlier during the interactive session by importing them from __main__ in the setup statement:

    >>> def f(x):
    ...     return x * x 
    ... 
    >>> import timeit
    >>> timeit.repeat("for x in range(100): f(x)", "from __main__ import f",
                      number=100000)
    [2.0640320777893066, 2.0876040458679199, 2.0520210266113281]
    

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon