"Barry A. Warsaw" wrote:
>
> I've just uploaded PEP 231, which describes a new hook in the instance
> access mechanism, called __findattr__() after a similar mechanism that
> exists in Jython (but is not exposed at the Python layer).
Ok, as I announced already, here some thoughts on __findattr__,
system state, and how it could work.
Looking at your patch, I realize that you are blocking __findattr__
for your whole instance, until this call ends.
This is not what you want to do, I guess. This has an effect of
affecting the whole system state when threads are involved.
Also you cannot use __findattr__ on any other attribute during
this call.
You want most probably do this:
__findattr__ should not be invoked again for this instance,
with this attribute name, for this "thread", until you are done.
The correct way to find out whether __findattr__ is active or
not would be to look upwards the frame chain and inspect it.
Moshe also asked about continuations: I think this would resolve
quite fine. However we jump around, the current chain of frames
dictates the semantics of __findattr__. It even applies to
Guido's tamed coroutines, given that an explicit switch were
allowed in the context of __findattr__.
In a sense, we get some kind of dynamic context here, since
we need to do a lookup for something in the dynamic call chain.
I guess this would be quite messy to implement, and inefficient.
Isn't there a way to accomplish the desired effect without
modifying the instance? In the context of __findattr__, *we*
know that we don't want to get a recursive call.
Let's assume __getattr__ and __setattr__ had yet another
optional parameter: infindattr, defaulting to 0.
We would than have to pass a positive value in this context,
which would object.c tell to not try to invoke __findattr__
again.
With explicit passing of state, no problems with threads
can occour. Readability might improve as well.
cheers - chris
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