random.SystemRandom().randint() inefficient
Cecil Westerhof
Cecil at decebal.nl
Wed Jul 27 13:24:14 EDT 2022
MRAB <python at mrabarnett.plus.com> writes:
> On 27/07/2022 16:43, Cecil Westerhof via Python-list wrote:
>> "Michael F. Stemper" <michael.stemper at gmail.com> writes:
>>
>>> 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
>>> >>>
>> Yes, I try to select a random element, but it has also to be removed,
>> because an element should not be used more as once.
>> This is the code I use:
>> # index = randbelow(len(to_try))
>> index = randrange(len(to_try))
>> found = permutation[to_try.pop(index)]
>>
>
> When you pop an element from the last, the elements after it need to be
> moved down, which takes time.
>
> Try shuffling the list and then popping the now randomly-ordered
> elements off the end.
Would shuffling not be a lot more expensive? Especially because I do
not eat the whole list.
--
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof
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