Re: [Python-Dev] Concerns about method overriding and subclassing with dataclasses

2018-01-01 Thread Chris Barker 
On Sat, Dec 30, 2017 at 7:27 AM, Stephen J. Turnbull <
[email protected]> wrote:

>   Just use the simple rule that a new
> __repr__ is generated unless provided in the dataclass.
>

are we only talking about __repr__ here ???

I interpretted Guido's proposal as being about all methods -- we _may_ want
something special for __repr__, but I hope not.

But +1 for Guido's proposal, not only because it's easy to explain, but
because it more naturally follows the usual inheritance logic:

The decorator's entire point is to auto-generate boilerplate code for you.
Once it's done that it shouldn't, in the end, behave any differently than
if you hand wrote that code. If you hand wrote the methods that the
decorator creates for you, they would override any base class versions. So
that's what it should do.

And the fact that you can optionally tell it not to in some particular case
keeps full flexibility.

-CHB

> I grant that there may be many reasons why one would be deriving

> dataclasses from dataclasses


Will you get the "right" __repr__ now if you derive a datacalss from a
dataclass? That would be a nice feature.

-CHB

-- 

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R(206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115   (206) 526-6317   main reception

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Re: [Python-Dev] Concerns about method overriding and subclassing with dataclasses

2018-01-01 Thread Ethan Smith 
On Mon, Jan 1, 2018 at 5:03 PM, Chris Barker  wrote:

> On Sat, Dec 30, 2017 at 7:27 AM, Stephen J. Turnbull <
> [email protected]> wrote:
>
>>   Just use the simple rule that a new
>> __repr__ is generated unless provided in the dataclass.
>>
>
> are we only talking about __repr__ here ???
>
> I interpretted Guido's proposal as being about all methods -- we _may_
> want something special for __repr__, but I hope not.
>
> But +1 for Guido's proposal, not only because it's easy to explain, but
> because it more naturally follows the usual inheritance logic:
>
> The decorator's entire point is to auto-generate boilerplate code for you.
> Once it's done that it shouldn't, in the end, behave any differently than
> if you hand wrote that code. If you hand wrote the methods that the
> decorator creates for you, they would override any base class versions. So
> that's what it should do.
>
> And the fact that you can optionally tell it not to in some particular
> case keeps full flexibility.
>
> -CHB
>

I interpreted this to be for all methods as well, which makes sense.
Special casing just __repr__ doesn't make sense to me, but I will wait for
Guido to clarify.

>
> > I grant that there may be many reasons why one would be deriving
>
>> dataclasses from dataclasses
>
>
> Will you get the "right" __repr__ now if you derive a datacalss from a
> dataclass? That would be a nice feature.
>

The __repr__ will be generated by the child dataclass unless the user
overrides it. So I believe this is the "right" __repr__.

~>Ethan Smith

>
> -CHB
>
> --
>
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R(206) 526-6959   voice
> 7600 Sand Point Way NE   (206) 526-6329   fax
> Seattle, WA  98115   (206) 526-6317   main reception
>
> [email protected]
>
> ___
> Python-Dev mailing list
> [email protected]
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> Unsubscribe: https://mail.python.org/mailman/options/python-dev/
> ethan%40ethanhs.me
>
>
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Re: [Python-Dev] Concerns about method overriding and subclassing with dataclasses

2018-01-01 Thread Chris Barker 
On Mon, Jan 1, 2018 at 7:50 PM, Ethan Smith  wrote:

>
> Will you get the "right" __repr__ now if you derive a datacalss from a
>> dataclass? That would be a nice feature.
>>
>
>
> The __repr__ will be generated by the child dataclass unless the user
> overrides it. So I believe this is the "right" __repr__.
>

what I was wondering is if the child will know about all the fields in the
parent -- so it could make a full __repr__.

-CHB




> ~>Ethan Smith
>
>>
>> -CHB
>>
>> --
>>
>> Christopher Barker, Ph.D.
>> Oceanographer
>>
>> Emergency Response Division
>> NOAA/NOS/OR&R(206) 526-6959   voice
>> 7600 Sand Point Way NE
>> 
>>   (206) 526-6329   fax
>> Seattle, WA  98115   (206) 526-6317   main reception
>>
>> [email protected]
>>
>> ___
>> Python-Dev mailing list
>> [email protected]
>> https://mail.python.org/mailman/listinfo/python-dev
>> Unsubscribe: https://mail.python.org/mailman/options/python-dev/ethan%
>> 40ethanhs.me
>>
>>
>


-- 

Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R(206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115   (206) 526-6317   main reception

[email protected]
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Re: [Python-Dev] Concerns about method overriding and subclassing with dataclasses

2018-01-01 Thread Guido van Rossum 
On Mon, Jan 1, 2018 at 8:50 PM, Ethan Smith  wrote:

>
>
> On Mon, Jan 1, 2018 at 5:03 PM, Chris Barker 
> wrote:
>
>> On Sat, Dec 30, 2017 at 7:27 AM, Stephen J. Turnbull <
>> [email protected]> wrote:
>>
>>>   Just use the simple rule that a new
>>> __repr__ is generated unless provided in the dataclass.
>>>
>>
>> are we only talking about __repr__ here ???
>>
>> I interpreted Guido's proposal as being about all methods -- we _may_
>> want something special for __repr__, but I hope not.
>>
> [...]
>>
>
> I interpreted this to be for all methods as well, which makes sense.
> Special casing just __repr__ doesn't make sense to me, but I will wait for
> Guido to clarify.
>

Indeed, I just wrote __repr__ for simplicity. This should apply to all
special methods. (Though there may be some complications for __eq__/__ne__
and for the ordering operators.)

On Mon, Jan 1, 2018 at 9:44 PM, Chris Barker  wrote:

> On Mon, Jan 1, 2018 at 7:50 PM, Ethan Smith  wrote:
>
>>
>> Will you get the "right" __repr__ now if you derive a dataclass from a
>>> dataclass? That would be a nice feature.
>>>
>>
>>
>>
> The __repr__ will be generated by the child dataclass unless the user
>> overrides it. So I believe this is the "right" __repr__.
>>
>
> what I was wondering is if the child will know about all the fields in the
> parent -- so it could make a full __repr__.
>

Yes, there's a class variable (__dataclass_fields__) that identifies the
parent fields. The PEP doesn't mention this or the fact that special
methods (like __repr__ and __init__) can tell whether a base class is a
dataclass. It probably should though. (@Eric)

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