Instead of bad hacks trying to worm around the inherited

object.__reduce__, do a getattr() on the class so we can explicitly
test for it.  The reduce()-calling code becomes a bit more regular as
a result.

Also add support slots: if an object has slots, the default state is
(dict, slots) where dict is the __dict__ or None, and slots is a dict
mapping slot names to slot values.  We do a best-effort approach to
find slot names, assuming the __slots__ fields of classes aren't
modified after class definition time to misrepresent the actual list
of slots defined by a class.

Lib/pickle.py

@@ -251,10 +251,7 @@ def get(self, i, pack=struct.pack):
 
         return GET + `i` + '\n'
 
-    def save(self, obj,
-             _builtin_type = (int, long, float, complex, str, unicode,
-                              tuple, list, dict),
-             ):
+    def save(self, obj):
         # Check for persistent id (defined by a subclass)
         pid = self.persistent_id(obj)
         if pid:
@@ -285,20 +282,24 @@ def save(self, obj,
 
         # Check copy_reg.dispatch_table
         reduce = dispatch_table.get(t)
-        if reduce:
-            rv = reduce(obj)
-        else:
-            # Check for __reduce__ method
-            reduce = getattr(obj, "__reduce__", None)
-            if not reduce:
-                # Check for instance of subclass of common built-in types
-                if self.proto >= 2 and isinstance(obj, _builtin_type):
-                    assert t not in _builtin_type # Proper subclass
+        if not reduce:
+            # Check for a __reduce__ method.
+            # Subtle: get the unbound method from the class, so that
+            # protocol 2 can override the default __reduce__ that all
+            # classes inherit from object.  This has the added
+            # advantage that the call always has the form reduce(obj)
+            reduce = getattr(t, "__reduce__", None)
+            if self.proto >= 2:
+                # Protocol 2 can do better than the default __reduce__
+                if reduce is object.__reduce__:
+                    reduce = None
+                if not reduce:
                     self.save_newobj(obj)
                     return
+            if not reduce:
                 raise PicklingError("Can't pickle %r object: %r" %
                                     (t.__name__, obj))
-            rv = reduce()
+        rv = reduce(obj)
 
         # Check for string returned by reduce(), meaning "save as global"
         if type(rv) is StringType:
@@ -320,13 +321,6 @@ def save(self, obj,
             raise PicklingError("Tuple returned by %s must have "
                                 "exactly two or three elements" % reduce)
 
-        # XXX Temporary hack XXX
-        # Override the default __reduce__ for new-style class instances
-        if self.proto >= 2:
-            if func is _reconstructor:
-                self.save_newobj(obj)
-                return
-
         # Save the reduce() output and finally memoize the object
         self.save_reduce(func, args, state)
         self.memoize(obj)
@@ -375,10 +369,11 @@ def save_reduce(self, func, args, state=None):
     def save_newobj(self, obj):
         # Save a new-style class instance, using protocol 2.
         # XXX Much of this is still experimental.
+        assert self.proto >= 2          # This only works for protocol 2
         t = type(obj)
         getnewargs = getattr(obj, "__getnewargs__", None)
         if getnewargs:
-            args = getnewargs() # This better not reference obj
+            args = getnewargs()         # This bette not reference obj
         else:
             for cls in int, long, float, complex, str, unicode, tuple:
                 if isinstance(obj, cls):
@@ -409,10 +404,32 @@ def save_newobj(self, obj):
 
         getstate = getattr(obj, "__getstate__", None)
         if getstate:
-            state = getstate()
-        else:
+            try:
+                state = getstate()
+            except TypeError, err:
+                # XXX Catch generic exception caused by __slots__
+                if str(err) != ("a class that defines __slots__ "
+                                "without defining __getstate__ "
+                                "cannot be pickled"):
+                    print repr(str(err))
+                    raise # Not that specific exception
+                getstate = None
+        if not getstate:
             state = getattr(obj, "__dict__", None)
-            # XXX What about __slots__?
+            # If there are slots, the state becomes a tuple of two
+            # items: the first item the regular __dict__ or None, and
+            # the second a dict mapping slot names to slot values
+            names = _slotnames(t)
+            if names:
+                slots = {}
+                nil = []
+                for name in names:
+                    value = getattr(obj, name, nil)
+                    if value is not nil:
+                        slots[name] = value
+                if slots:
+                    state = (state, slots)
+
         if state is not None:
             save(state)
             write(BUILD)
@@ -718,6 +735,24 @@ def save_global(self, obj, name = None):
 
 # Pickling helpers
 
+def _slotnames(cls):
+    """Return a list of slot names for a given class.
+
+    This needs to find slots defined by the class and its bases, so we
+    can't simply return the __slots__ attribute.  We must walk down
+    the Method Resolution Order and concatenate the __slots__ of each
+    class found there.  (This assumes classes don't modify their
+    __slots__ attribute to misrepresent their slots after the class is
+    defined.)
+    """
+    if not hasattr(cls, "__slots__"):
+        return []
+    names = []
+    for c in cls.__mro__:
+        if "__slots__" in c.__dict__:
+            names += list(c.__dict__["__slots__"])
+    return names
+
 def _keep_alive(x, memo):
     """Keeps a reference to the object x in the memo.
 
@@ -1152,22 +1187,29 @@ def load_setitems(self):
 
     def load_build(self):
         stack = self.stack
-        value = stack.pop()
+        state = stack.pop()
         inst = stack[-1]
-        try:
-            setstate = inst.__setstate__
-        except AttributeError:
+        setstate = getattr(inst, "__setstate__", None)
+        if setstate:
+            setstate(state)
+            return
+        slotstate = None
+        if isinstance(state, tuple) and len(state) == 2:
+            state, slotstate = state
+        if state:
             try:
-                inst.__dict__.update(value)
+                inst.__dict__.update(state)
             except RuntimeError:
-                # XXX In restricted execution, the instance's __dict__ is not
-                # accessible.  Use the old way of unpickling the instance
-                # variables.  This is a semantic different when unpickling in
-                # restricted vs. unrestricted modes.
-                for k, v in value.items():
+                # XXX In restricted execution, the instance's __dict__
+                # is not accessible.  Use the old way of unpickling
+                # the instance variables.  This is a semantic
+                # difference when unpickling in restricted
+                # vs. unrestricted modes.
+                for k, v in state.items():
                     setattr(inst, k, v)
-        else:
-            setstate(value)
+        if slotstate:
+            for k, v in slotstate.items():
+                setattr(inst, k, v)
     dispatch[BUILD] = load_build
 
     def load_mark(self):