Re: Two aces up Python's sleeve

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