CODEWITHSUNDEEP
pythonpython-3.x
Kifsif
Kifsif

Reputation: 3843

Benchmark Python programs

I'm new to Python. It is my first interpreted language. I used to study Java so far. So, when Java program runs for the first time, it is execueted slower than for the next times. The reasi is caching. 

import time

def procedure():
    time.sleep(2.5)

# measure process time
t0 = time.clock()
procedure()
print (time.clock() - t0), "seconds process time"

I tried this for several times. The result is always equal. So, am I right that no cashe interferes and that the benchmark is pretty reliable?

Upvotes: 3

Views: 357

Answers (1)

ch3ka
ch3ka

Reputation: 12158

it's OK to do benchmarks like this, the accuracy is good enough for functions which run "long" and pretty constant, like in your example. But there are some pitfalls: for "quick" functions (like the empty one), you run into precision limits. And for functions which vary in execution time (like net i/o, for example), you have to measure multiple times to find min/max/avg runtime. And in addition to that, the clock best used differs on platforms: on windows, time.clock() is preferred, on *nix, time.time().

luckily, there is a module which takes care of all that: timeit:

>>> import time
>>> def procedure():
    pass

>>> def time_this(f):
    t0=time.clock()
    f()
    print((time.clock() - t0), "seconds process time")


>>> time_this(procedure)
1.9555558310457855e-06 seconds process time
>>> time_this(procedure)
1.9555557742023666e-06 seconds process time
>>> time_this(procedure)
1.9555557742023666e-06 seconds process time
>>> import timeit
>>> timeit.Timer(procedure).timeit()
0.09460783423588737
>>> timeit.Timer(procedure).repeat()
[0.09791419021132697, 0.09721947901198291, 0.09598943441130814]

you might want to look at it's source. Or just use it ;)

As for caching: python code compiles to bytecode when first used. This bytecode is cached by default - but this won't affect your benchmark as long as you don't do imports in your function.

Upvotes: 5

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