random.SystemRandom().randint() inefficient
MRAB
python at mrabarnett.plus.com
Wed Jul 27 12:30:48 EDT 2022
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.
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