[Python-Dev] collections.abc for data and non-data descriptors

[Roberto Martínez]

Oh, I understand. Maybe is not worth the effort anyway.

Thank you

El mar., 17 ene. 2017 a las 19:40, Guido van Rossum (<guido at python.org>)
escribió:

But you can never get people to use the new ABCs consistently.

Anyway, I'm not -1, I'm just -0 -- I don't think it'll make any difference
and you're better off just checking for __set__ (if it only has __set__ but
not __get__, do you care what it is?).

On Tue, Jan 17, 2017 at 10:18 AM, Roberto Martínez <
robertomartinezp at gmail.com> wrote:

Well, for me having to check both __get__ and __str__ for a data descriptor
feels inelegant.

After read the documentation of collections.abc again "This module provides
abstract base classes that can be used to test whether a class provides a
particular interface; for example, whether it is hashable or whether it is
a mapping." I ask: what is the criteria to decide which interfaces are
worth implemented as an ABC in the standard library?

To my understanding, any well defined python protocol should have a proper
ABC.

El mar., 17 ene. 2017 a las 18:55, Guido van Rossum (<guido at python.org>)
escribió:

For this use case I see nothing wrong with hasattr(myobj, '__set__').

On Tue, Jan 17, 2017 at 9:41 AM, Roberto Martínez <
robertomartinezp at gmail.com> wrote:

I need to check if some objects obey the descriptor protocol in the
construction of a metaclass. I expect to be able to write something like:

if isinstance(myobj, abc.DataDescriptor):
   # do something

The other idea crossing my mind is something like:

if all(hasattr(myobj, attr) for attr in ('__get__', '__set__')):
    # do something


El mar., 17 ene. 2017 a las 18:07, Guido van Rossum (<guido at python.org>)
escribió:

Well, these are an example of the purest duck typing. Just implement
__get__ and/or __set__ (and __delete__) and you're good.

What's the situation where you miss them?

--Guido

On Tue, Jan 17, 2017 at 8:51 AM, Roberto Martínez <
robertomartinezp at gmail.com> wrote:

Hi,

I miss abstract base classes in collections.abc implementing the descriptor
protocol. Any reason why they do not exist?

What do you think of adding NonDataDescriptor and DataDescriptor ABCs?

Best regards,
Roberto

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-- 
--Guido van Rossum (python.org/~guido)




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--Guido van Rossum (python.org/~guido)




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--Guido van Rossum (python.org/~guido)
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