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[Python-Dev] Is static typing still optional?

On 01/29/2018 12:57 AM, Eric V. Smith wrote:
> On 1/29/2018 3:42 AM, Ethan Furman wrote:
>> On 01/28/2018 07:45 AM, Eric V. Smith wrote:

>>> I think the hashing logic explained in https://bugs.python.org/issue32513#msg310830 is correct. It uses hash=None as the
>>> default, so that frozen=True objects are hashable
>> In a class, `__hash__ = None` means the instances are not hashable... but in a dataclass decorator, `hash=None` means
>> they are?
> It means "don't add a __hash__ attribute, and rely on the base class value". But maybe it should mean "is not hashable".
> But in that case, how would we specify the "don't add __hash__" case?

I thought `hash=False` means don't add a __hash__ method..

> Note that "repr=False" means "don't add a __repr__", not "is not repr-able". And "init=False" means "don't add a
> __init__", not "is not init-able".

Yeah, like that.

I get that the default for all (or at least most) of the boring stuff should be "just do it", but I don't think None is 
the proper place-holder for that.  Why not make an `_default = object()` sentinel and use that for the default?  At 
least for __hash__.  Then we have:

hash=False  ->  don't add one

hash=None  -> add `__hash__ = None`  (is not hashable)

hash=True  -> add one (the default...

Okay, after writing that down, why don't we have the default value for anything automatically added be True?  With True 
meaning the dataclass should have a custom whatever, and if the programmer did not provide one the decorator will -- it 
can even be a self-check: if the parameters in the decorator are at odds with the actual class contents (hash=None, but 
the class has a __hash__ method) then an exception could be raised.