Hi! For the record: If the metaclass M of a new class C is dynamically created, for example from the metaclasses of the bases of C, then pickling of C indeed works after registering copy_reg.pickle(M, M.__reduce__).
Remark: I found some comments stating that the current use of metaclasses in Sage is not very scalable. I guess that shall be understood as "things get messy if one puts a new metaclass on top of existing (and different) metaclasses of the base classes". It seems to me that the approach to dynamically create new metaclasses from old would be better scalable. Example: I can easily put my FastHashMetaclass on top of the metaclass that comes with UniqueRepresentation. sage: class Foo(UniqueRepresentation): ....: __metaclass__ = FastHashMetaclass ....: def __init__(self,R): ....: self.R = R ....: def __repr__(self): ....: return "[%s]"%self.R ....: It has a dynamic metaclass, obtained from FastHashMetaclass and ClasscallMetaclass: sage: type(Foo) <class '_home_king_SAGE_work_fast_hash_fast_hash_pyx_1.FastHashAndClasscallMetaclass'> Pickling of the class works (which would, by the way, not work without my metaclass. See below): sage: loads(dumps(Foo)) <class '__main__.Foo'> Object creation and object pickling works as well. Thanks to inheritance from UniqueRepresentation, Foo instances are unique: sage: f = Foo(7) sage: f [7] sage: loads(dumps(f)) is f True Now, we compare with a similar class that doesn't use FastHashMetaclass: sage: class Bar(UniqueRepresentation): ....: def __init__(self,R): ....: self.R = R ....: def __repr__(self): ....: return "[%s]"%self.R ....: sage: b = Bar(8) # Pickling fails: sage: loads(dumps(b)) is b Traceback (most recent call last): ... PicklingError: Can't pickle <class '__main__.Bar'>: attribute lookup __main__.Bar failed And, as the name of the metaclass suggest: The hash is faster when one uses it: sage: %timeit hash(f) 625 loops, best of 3: 478 ns per loop sage: %timeit hash(b) 625 loops, best of 3: 1.06 µs per loop In some cases, the metaclass can be used to speed-up the hash *after* object creation: sage: P.<x> = QQ[] sage: %timeit hash(P) 625 loops, best of 3: 3.17 µs per loop sage: P.__class__ = FastHashMetaclass(P.__class__) sage: %timeit hash(P) 625 loops, best of 3: 453 ns per loop But in other cases, that won't work (for example, overriding the class of x won't work). To me, it seems like a potentially useful programming tool. I guess I will soon open a ticket. Best regards, Simon -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
