Behaviour of classes (tired of writing too much)

[mpn]

How do I catch any reference to an instance of a class, i.e., I want to
run some code as soon as an instance of a class is used in any way.
(and I don't want to define all of __add__, __ge__ etc etc etc etc etc)

The reason for the question is that I want to simplify the Message
Passing Interface (MPI) calls. I find it irritating that I have to
start a non-blocking send/receive and then check that the data has
arrived. Why not automagically check/wait for the data when it is
needed?

The second part that I also need to make that idea work is the ability
to change the instance to the received data, i.e., self=received data,
and then launch the original reference.

So I guess that the code I want to write is:

class MPI_tmp:
# temporary object that changes ITSELF into another object when
called in any way
def __on_any_call__(self):
self=newobject()
self.__run_the_anycall__()

which probably doesn't work :-)

Greatful for any ideas / Magnus

[Brian Quinlan]

mp*@mic.dtu.dk wrote:

How do I catch any reference to an instance of a class, i.e., I want to
run some code as soon as an instance of a class is used in any way.
(and I don't want to define all of __add__, __ge__ etc etc etc etc etc)

What do you mean by "used in any way"? Which of these are considered usage:

>>a = Foo() # obviously
b = a # ?
a.__gt__(5) # apparently
a.__gt__ # ?

Anyway, look into __getattr__

Cheers,
Brian

[Steve Holden]

mp*@mic.dtu.dk wrote:

How do I catch any reference to an instance of a class, i.e., I want to
run some code as soon as an instance of a class is used in any way.
(and I don't want to define all of __add__, __ge__ etc etc etc etc etc)

The reason for the question is that I want to simplify the Message
Passing Interface (MPI) calls. I find it irritating that I have to
start a non-blocking send/receive and then check that the data has
arrived. Why not automagically check/wait for the data when it is
needed?

The second part that I also need to make that idea work is the ability
to change the instance to the received data, i.e., self=received data,
and then launch the original reference.

So I guess that the code I want to write is:

class MPI_tmp:
# temporary object that changes ITSELF into another object when
called in any way
def __on_any_call__(self):
self=newobject()
self.__run_the_anycall__()

which probably doesn't work :-)

Greatful for any ideas / Magnus

Maybe it could make a damned fine cup of coffee as well ;-) ?

That's a pretty tall order, and mutating self isn't as simple as you
think. However you *can* change an instance's __class__ attribute
dynamically, which might be a way to get where you want. Not sure about
the "trapping all accesses" bit, though. __getattr__() could give you
access to undefined attributes.

For new_style classes you can implement __getattribute__() to trap *any*
attribute access. This would be somewhat slow, but might be acceptable
if you were then changing the instance's class to something that
*didn't* implement __getattribute__().

regards
Steve
--
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