[Python-bugs-list] [ python-Bugs-494904 ] Cannot pickle a class with a metaclass

[noreply@sourceforge.net]

Bugs item #494904, was opened at 2001-12-18 20:52
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=494904&group_id=5470

Category: Type/class unification
Group: Not a Bug
Status: Open
Resolution: None
Priority: 5
Submitted By: Dan Parisien (mathematician)
Assigned to: Nobody/Anonymous (nobody)
Summary: Cannot pickle a class with a metaclass

Initial Comment:
when pickle retrieves the __reduce__ method of a new 
style class that has a metaclass, instead of 
returning the metaclass's __reduce__ method bound to 
the class, it returns an unbound __reduce__ method of 
that class.

>>> class metaclass(type):
... 	def __reduce__(self):
... 		"""This is metaclass.__reduce__
... 		"""
... 		return type.__reduce__(self)
... 
>>> class newclass(object):
... 	__metaclass__ = metaclass
... 	def __reduce__(self):
... 		"""This is newclass.__reduce__
... 		"""
... 		return object.__reduce__(self)
... 
>>> print newclass.__reduce__.__doc__
This is newclass.__reduce__

when pickle calls object.__reduce__ on newclass, it 
returns an unbound newclass.__reduce__ and not a 
bound metaclass.__reduce__. This has the unfortunate 
side effect of not correctly 'reducing' the class. 
I'm trying to figure out a solution. 



----------------------------------------------------------------------

You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=494904&group_id=5470