On 26/07/2022 16.47, Cecil Westerhof wrote:
Chris Angelico <ros...@gmail.com> writes:
On Wed, 27 Jul 2022 at 06:06, Cecil Westerhof via Python-list
<python-list@python.org> wrote:
Chris Angelico <ros...@gmail.com> writes:
On Wed, 27 Jul 2022 at 01:06, Cecil Westerhof via Python-list
<python-list@python.org> wrote:
I need to get a random integer. At first I tried it with:
from secrets import randbelow
index = randbelow(len(to_try))
This works perfectly, but it took some time. So I thought I try:
from random import SystemRandom
index = SystemRandom().randint(0, len(to_try) - 1)
A first indication is that the second version would take about two
times as much time as the first. Is there a reason for this, or should
this not be happening?
You're setting up a brand new SystemRandom instance just for a single
random number. For a fairer comparison, set up the instance, then
generate far more than just a single number, and see how that goes.
Thanks. I thought I did something wrong and I did.
I will try to implement like you said and look what the result will
be. (And share it.)
Thanks! Don't feel bad; performance testing is *hard*, getting
meaningful results takes a lot of of fiddling with parameters, and
getting interesting AND meaningful results can sometimes seem about
impossible.
(As I understand it both do more, or less the same and should have
comparable performance.)
In normal production work? Yes (the SystemRandom object doesn't have
any significant state - a seeded RNG could have a lot more overhead
here). But for performance testing? The work of instantiating the
class could be completely irrelevant, or it could be dominating your
results. It's hard to say, hence the suggestion to try it without
reinstantiating.
It had a very big influence. Original it took about three times more
time to run my program. (The program was still running when I posted
the original post and the difference was higher as I anticipated.)
Removing that did cut about 45% of the execution time of the program.
(So the initiation is quit expensive.)
But it still takes about 50% more time. So I am still a bit
flabbergasted.
The new code:
from random import SystemRandom
system_random = SystemRandom()
index = system_random.randint(0, len(to_try) - 1)
This is orthogonal to your question, but might be of some use to you:
The combination of using len(to_try) as an argument to randint() and
saving the output to a variable named "index" suggests that you might
be setting up to select a random element from to_try, as in:
something = to_try[index]
If that is the case, you might want to consider using random.choice() instead:
>>> from random import choice
>>> to_try = [2,3,5,7,11,13,"seventeen",19]
>>> choice(to_try)
2
>>> choice(to_try)
'seventeen'
>>> choice(to_try)
13
>>> choice(to_try)
5
>>>
--
Michael F. Stemper
This sentence no verb.
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