Multi Heritage with slots

[Alexandre Badez]

Hye,

I'm developing a little app, and I want to make multi heritage.
My problem is that my both parent do have __slots__ define.

So I've got something like:

class foo(object):
__slots__ = ['a', 'b']
pass

class foo2(object):
__slots__ = ['c', 'd']
pass

class crash(foo, foo2):
pass

If you write only that in a sample file or in python console (as I
did), python refuse to load the module and report something like:

Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: Error when calling the metaclass bases
multiple bases have instance lay-out conflict

Do you know why it append? And how could I make this work?

 

[Eric Brunel]

Hye,

I'm developing a little app, and I want to make multi heritage.
My problem is that my both parent do have __slots__ define.

So I've got something like:

class foo(object):
__slots__ = ['a', 'b']
pass

class foo2(object):
__slots__ = ['c', 'd']
pass

class crash(foo, foo2):
pass

If you write only that in a sample file or in python console (as I
did), python refuse to load the module and report something like:

Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: Error when calling the metaclass bases
multiple bases have instance lay-out conflict

Do you know why it append? And how could I make this work?

See http://mail.python.org/pipermail/python-list/2006-December/418768.html

Basically, the general advice you're likely to get here is: don't use
__slots__, or at least don't use __slots__ with inheritance.

BTW, what are you trying to do? Is it really a memory footprint
optimization, which is the intended use case for __slots__, or are you
just doing Java in Python?

 

[Alexandre Badez]

Seehttp://mail.python.org/pipermail/python-list/2006-December/418768.html

Basically, the general advice you're likely to get here is: don't use
__slots__, or at least don't use __slots__ with inheritance.

BTW, what are you trying to do? Is it really a memory footprint
optimization, which is the intended use case for __slots__, or are you
just doing Java in Python?

Thanks for your answer.
I use __slots__ not for memory optimization nor doing java.
I use __slots__ because my class are used by other lib, and in the
past, some of them misspell some attributes and involved a very
annoying comportment of the global application.
So the objective is only to prevent unwanted dynamism (but not in all
the application, just some class).

PS: I very like your signature

 

[Simon Brunning]

I use __slots__ not for memory optimization nor doing java.
I use __slots__ because my class are used by other lib, and in the
past, some of them misspell some attributes and involved a very
annoying comportment of the global application.
So the objective is only to prevent unwanted dynamism (but not in all
the application, just some class).

Using slots to prevent the creation of new properties is what Eric
*means* by "doing java". You're trying to write Java style code in
Python, and it's not going to be pretty. Slots are not intended for
this purpose, and they aren't very good for it.

--
Cheers,
Simon B.
(e-mail address removed)
http://www.brunningonline.net/simon/blog/
GTalk: simon.brunning | MSN: small_values | Yahoo: smallvalues

 

[Michele Simionato]

Using slots to prevent the creation of new properties is what Eric
*means* by "doing java". You're trying to write Java style code in
Python, and it's not going to be pretty. Slots are not intended for
this purpose, and they aren't very good for it.

Right, and this the way to do what the original poster wants:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/252158

Michele Simionato

 

[Alexandre Badez]

Right, and this the way to do what the original poster wants:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/252158

Michele Simionato

Thanks every body for your remarks.
I still have a lot to learn in python...