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
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