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From: dn <PythonList@DancesWithMice.info>
Newsgroups: comp.lang.python
Subject: Re: Two aces up Python's sleeve
Date: Fri, 8 Nov 2024 13:07:48 +1300
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On 8/11/24 11:15, Greg Ewing via Python-list wrote:
> On 8/11/24 3:04 am, Mild Shock wrote:
>> This only works for small integers. I guess
>> this is because tagged pointers are used
>> nowadays ?
> 
> No, it's because integers in a certain small range are cached. Not sure 
> what the actual range is nowadays, it used to be something like -5 to 
> 256 I think.
> 
> BTW you have to be careful testing this, because the compiler sometimes 
> does constant folding, so you need to be sure it's actually computing 
> the numbers at run time.

Haven't seen the OP. Is the Newsgroup link forwarding to the email-list 
correctly?


Integer interning is indeed valid for -5 <= i <= 256
("it works on my machine"! see below)

 >>> a = 0; b = 0; c = 0; d = 0
 >>> while a is b:
....     print( a, b, end=" ", )
....     print( c, d, ) if c is d else print()
....     a += 1; b += 1; c -= 1; d -= 1
....
0 0 0 0
1 1 -1 -1
2 2 -2 -2
3 3 -3 -3
4 4 -4 -4
5 5 -5 -5
6 6
7 7
8 8
9 9
....
254 254
255 255
256 256
 >>>

Be aware that this is implementation-dependent and not guaranteed to 
hold forever.

  dn  ~  python
Python 3.12.7 (main, Oct  1 2024, 00:00:00) [GCC 13.3.1 20240913 (Red 
Hat 13.3.1-3)] on linux
Type "help", "copyright", "credits" or "license" for more information.


See also https://docs.python.org/3/library/sys.html#sys.intern

Thus could decide what is interned for yourself:

a_string = sys.intern( str( 1000 ) )

-- 
Regards,
=dn