[Python-Dev] Type of range object members

["Martin v. Löwis"]

Neal Norwitz schrieb:
> 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. :-)

There are common schemes that allow constant-time issubclass tests,
although they do require more memory:

1. give each base class a small unique number, starting with 1
   (0 means no number has been assigned). Give each class a bitmap
   of all base classes, plus a field for the maximum-numbered
   base class. Then,

   def issubclass(C, B):
     return B.classnum and (B.classnum < C.maxbasenum) and\
            bit_set(C.basenums, B.classnum)

   Supports multiple inheritance, space requirement linear
   with the number of classes that are used as base classes.
   Numbering should recycle class numbers when a class is
   gced.

2. restrict optimization to single-inheritance. Give each class
   a "depth" (distance from object, 0 for object and
   multiply-inherited classes). Also give each class an array
   of bases, ordered by depth. Then,

   def issubclass(C, B):
     if not C.depth: return expensive_issubclass(C, B)
     return B.depth < C.depth and (C.bases[B.depth] is B)

   Space requirement is linear with the depth of the class
   (but I think tp_mro could be used, if the formula is
    changed to (C.bases[C.depth-B.depth] is B))

Regards,
Martin