random.SystemRandom().randint() inefficient

Wed Jul 27 14:55:26 EDT 2022

On 27/07/2022 18:24, Cecil Westerhof via Python-list wrote:
> 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.
>You won't know until you time it.