random.SystemRandom().randint() inefficient

[Cecil Westerhof]

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