[Python-ideas] Re: frozen dataclasses attribute initialization

[Eric V. Smith]

On 12/12/2019 8:07 AM, Arthur Pastel wrote:

    On Thu, Dec 12, 2019 at 2:03 AM Eric V. Smith <e...@trueblade.com
    <mailto:e...@trueblade.com>> wrote:

        On 12/11/2019 6:36 PM, Arthur Pastel wrote:
        >> Add an extra hidden attribute to every instance just
        >> to track whether you’re inside __post_init__ so
        __setattr__ can check it?
        I don't want to add attributes that weren't defined in the
        class definition.

    Would it be okay if we create an instance attribute before
    calling the __init__ and then we remove it after the __post_init__ ?
    Then we would simply have to check for the attribute existence
    when checking if we raise a FrozenInstanceError.

    That wouldn't work if the class used __slots__.


 Then, in this specific case, would it be possible to add the 
attribute to the __slots__ in the generated class ?

No, __slots__ can't be added or modified after the class exists (which 
is why @dataclass doesn't have an option to add __slots__).

Eric


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