[Python-Dev] Type of range object members

[Phillip J. Eby]

At 11:46 PM 8/15/2006 -0700, Neal Norwitz wrote:
>On 8/15/06, "Martin v. Löwis" <martin at v.loewis.de> wrote:
>>
>>That penalty is already paid today. Much code dealing with
>>ints has a type test whether it's an int or a long. If
>>int and long become subtypes of each other or of some abstract
>>type, performance will decrease even more because a subtype
>>test is quite expensive if the object is neither int nor
>>long (it has to traverse the entire base type hierarchy to
>>find out its not inherited from int).
>
>I was playing around with a little patch to avoid that penalty.  It
>doesn't take any additional memory, just a handful of bits we aren't
>using. :-)
>
>For the more common builtin types, it stores whether it's a subclass
>in tp_flags, so there's no function call necessary and it's a constant
>time operation.  It was faster when doing simple stuff.  Haven't
>thought much whether this is really worthwhile or not.

It seems to me that you could drop the FAST_SUBCLASS bit, since none of the 
other bits will be set if it is not a subclass of a builtin.  That would 
free up one flag bit -- perhaps usable for that BaseException flag Guido 
wants.  :)

(Of course, if you can't inherit from both BaseException and one of the 
other builtin types, it can just be another enumeration value within the 
bit mask.)