Re: [ZODB-Dev] PersistentMapping

2005-11-17 Thread Jeremy Hylton 
On 11/17/05, Thomas Lotze [EMAIL PROTECTED] wrote:
 Hi,

 I just noticed two things about persistent.PersistentMapping:

 - It inherits from UserDict.UserDict. Is there any reason not to inherit
   from dict directly, given that this has been possible since Python 2.3
   IIRC?

It has been possible to inherit from dictionary since Python 2.2, but
it is not possible for a persistent object and it would not do what
you expect even if it were possible.  A persistent object has a custom
C layout and so does dict, so it is not possible to have them both as
base classes.  (TypeError: multiple bases have instance lay-out
conflict.  (I don't know why there is a hypen in lay-out.))  If it
were possible, it wouldn't work anyway.  If you inherit from dict and
override its builtin methods, like __setitem__, your overridden method
will be ignored by C code using methods like PyDict_SetItem().

 - Not all methods of the mapping interface are handled. In particular,
   there's no reason not to handle pop() as popitems() is handled.
   Unhandled methods that change the content of the dict lead to especially
   nasty bugs as they seem to work OK during a transaction while their
   effect is not permanent.

On the other hand, I think that this omission is just an oversight. 
It would probably be a good idea to change PersistentDict/Mapping to
use the DictMixin instead of UserDict.

Jeremy
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Re: [ZODB-Dev] PersistentMapping glitches

2005-08-23 Thread Victor Safronovich 
Hello Tim Peters,

Monday, August 22, 2005, 8:44:08 PM, you wrote:

 from BTrees.OOBTree import OOBTree 
 b = OOBTree()
 b.update(pm)
TP Traceback (most recent call last):
TP   File stdin, line 1, in ?
TP   File C:\python23\lib\UserDict.py, line 19, in __getitem__
TP def __getitem__(self, key): return self.data[key]
TP KeyError: 0

Some  workaround for me(the Collector 1873 poster) was to use data attribute of
the UserDict instances.
 from ZODB.PersistentMapping import PersistentMapping
 from BTrees.OOBTree import OOBTree
 r = OOBTree()
 r.update( PersistentMapping({1:1}).data)
 dict(r)
{1: 1}

i am using isinstance(obj, UserDict) condition now.

-- 
Best regards,
 Victor Safronovich
 NauMen.NauDoc.SoftwareDeveloper  http://www.naumen.ru

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