By using this site, you agree to our updated Privacy Policy and our Terms of Use. Manage your Cookies Settings.
440,551 Members | 1,142 Online
Bytes IT Community
+ Ask a Question
Need help? Post your question and get tips & solutions from a community of 440,551 IT Pros & Developers. It's quick & easy.

Recursion with __setattr__

P: n/a
Operating Ubunutu Linux 5.04 on iMac 333mhz
Python 2.4.1 in IDLE 1.1.1

In trying to create a interactive drawing framework in Python I came across
the idea of binding attributes of one object to attributes of another.

The way it works is when obj1.attr1 is set obj2.attr2 should have it's
__setattr__ method called as well. But it ends up giving me a recursion error.

The attribute synchronization is shown below:


def sync(attr1,obj1,obj2,attr2=None):
"""Synchronize attribute access

name of attribute to synchronize
(optional) attribute name to use when setting second object.
if not attr2: attr2 = attr1
# rename old __setattr__'s
obj1.__old_setattr__ = obj1.__setattr__
obj2.__old_setattr__ = obj2.__setattr__
except AttributeError: pass
# modify mirrored attributes on attribute change
def hook_setattr(inst):
# Hey! Only classes have special methods!
class sethook(inst.__class__):
def __setattr__(self,name,value):
except AttributeError: pass
if name in self.__syncdict__:
entry = self.__syncdict__[name]
for mirror,attr in entry: pass
# recursion error here: setattr(mirror,attr,value)
#sethook.__name__ = inst.__class__.__name__ # magic?
inst.__class__ = sethook
# append synchronization info
except AttributeError:
obj1.__syncdict__ = {attr1: [(obj2,attr2)]}
except AttributeError:
obj2.__syncdict__ = {attr2: [(obj1,attr1)]}
# make the magic work

When I try to call this like sync('attr',obj,obj2) I get a recursion error.
I could understand this happening if I was calling setattr on itself, but
why the other object?

Any help is greatly appreciated. Also, any pointers on efficiency or easier
ways is also welcome. Thanks in

Oct 16 '05 #1
Share this question for a faster answer!
Share on Google+

This discussion thread is closed

Replies have been disabled for this discussion.