Add a magical feature to save_reduce so that __reduce__ can cause
NEWOBJ to be generated.
diff --git a/Lib/pickle.py b/Lib/pickle.py
index 5106ec9..bb840c9 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -365,9 +365,46 @@
save = self.save
write = self.write
- save(func)
- save(args)
- write(REDUCE)
+ # Protocol 2 special case: if func's name is __newobj__, use NEWOBJ
+ if self.proto >= 2 and getattr(func, "__name__", "") == "__newobj__":
+ # A __reduce__ implementation can direct protocol 2 to
+ # use the more efficient NEWOBJ opcode, while still
+ # allowing protocol 0 and 1 to work normally. For this to
+ # work, the function returned by __reduce__ should be
+ # called __newobj__, and its first argument should be a
+ # new-style class. The implementation for __newobj__
+ # should be as follows, although pickle has no way to
+ # verify this:
+ #
+ # def __newobj__(cls, *args):
+ # return cls.__new__(cls, *args)
+ #
+ # Protocols 0 and 1 will pickle a reference to __newobj__,
+ # while protocol 2 (and above) will pickle a reference to
+ # cls, the remaining args tuple, and the NEWOBJ code,
+ # which calls cls.__new__(cls, *args) at unpickling time
+ # (see load_newobj below). If __reduce__ returns a
+ # three-tuple, the state from the third tuple item will be
+ # pickled regardless of the protocol, calling __setstate__
+ # at unpickling time (see load_build below).
+ #
+ # Note that no standard __newobj__ implementation exists;
+ # you have to provide your own. This is to enforce
+ # compatibility with Python 2.2 (pickles written using
+ # protocol 0 or 1 in Python 2.3 should be unpicklable by
+ # Python 2.2).
+ cls = args[0]
+ if not hasattr(cls, "__new__"):
+ raise PicklingError(
+ "args[0] from __newobj__ args has no __new__")
+ args = args[1:]
+ save(cls)
+ save(args)
+ write(NEWOBJ)
+ else:
+ save(func)
+ save(args)
+ write(REDUCE)
if state is not None:
save(state)
@@ -375,7 +412,6 @@
def save_newobj(self, obj):
# Save a new-style class instance, using protocol 2.
- # XXX This is still experimental.
assert self.proto >= 2 # This only works for protocol 2
t = type(obj)
getnewargs = getattr(obj, "__getnewargs__", None)