the stack, allowing it to be retrieved from the memo
      repeatedly if several instances of the same class are created.  This
      can be much more efficient (in both time and space) than repeatedly
      embedding the module and class names in INST opcodes.

      Unlike INST, OBJ takes no arguments from the opcode stream.  Instead
      the class object is taken off the stack, immediately above the
      topmost markobject:

      Stack before: ... markobject classobject stackslice
      Stack after:  ... new_instance_object

      As for INST, the remainder of the stack above the markobject is
      gathered into an argument tuple, and then the logic seems identical,
      except that no __safe_for_unpickling__ check is done (XXX this is
      a bug).  See INST for the gory details.

      NOTE:  In Python 2.3, INST and OBJ are identical except for how they
      get the class object.  That was always the intent; the implementations
      had diverged for accidental reasons.
      