pickle and weakref

Nagy László nagylzs at freemail.hu
Fri Jan 10 14:57:26 CET 2003

I wonder if there is a standard way to pickle/unpickle weak references.
My idea is the following:

import pickle
import weakref

class A:

a = A()
b = A()
c = A()

a.b = b
a.ref_b = weakref.ref(b)
a.ref_c = weakref.ref(c)

data = pickle.dumps(a)
a = pickle.loads(data)

print a             # <__main__.A instance at 0X???? >
print a.b          # <__main__.A instance at 0X????>
print a.c          # None
print a.ref_b    # <weakref at 0x???? to 'instance' at 0x????>, 
references to pickled instances should be unpickled gracefully
print a.ref_c    # <weakref at ????; dead>, references to other (not 
pickled) instances should be unpickled as a dead reference

I've already written a wrapper class to do this but it is not a general 
solution. My wrapper uses the 'Ownership' concept and
can pickle weak references to instances of a given class only.

This extension should not affect older codes because they don't pickle 
any weak references.
What do you think? Is this a good idea?

  Laci 1.0

More information about the Python-list mailing list