[Python-Dev] Possible low-hanging optimization

[David Abrahams]

In Boost.Python, extension class instance dictionaries are created
only on-demand.  It's an obvious win for lots of wrapped C++ class
instances, which will never have Python attributes tacked on.  This
also seems like a potential big win for some kinds of Python
instances, like those which use __slots__ but may also have a
dictionary (IIRC that is a possible configuration).  The code to do
this in Boost.Python is small and "just works" transparently, so I
thought there might be some interest here for the Python core:

I've "C-ified" the code here, sort of on-the-fly, just to give an
idea, but it's so simple that any errors can't obscure the intent
/too/ much ;-)

      static PyObject* instance_get_dict(PyObject* op, void*)
      {
          bpl_instance* inst = (bpl_instance*)op;
          if (inst->dict == 0)
              inst->dict = PyDict_New();
          Py_XINCREF(inst->dict);
          return inst->dict;
      }
    
      static int instance_set_dict(PyObject* op, PyObject* dict, void*)
      {
          (bpl_instance)* inst = (bpl_instance*)op;
          Py_XDECREF(inst->dict);
          Py_XINCREF(dict);
          inst->dict = dict
          return 0;
      }

  static PyGetSetDef instance_getsets[] = { /* used as tp_getset */
      {"__dict__",  instance_get_dict,  instance_set_dict, NULL},
      {0}
  };

Useful?

-Dave

-- 
                       David Abrahams
   dave@boost-consulting.com * http://www.boost-consulting.com
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