typing the untype-able with mypy plugins (advanced) anthony explains

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typing the untype-able with mypy plugins (advanced) anthony explains

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Күн бұрын

today I show an approach to make mypy understand a very dynamic pattern with a plugin!
playlist: • anthony explains
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Пікірлер: 23

@alessio622 2 ай бұрын

Very very interesting topic. I’m using this to implement a plugin for factoryboy type annotations (types-factoryboy). It’d be great to have more videos like this explaining how to write mypy plugins, as there is very little “digested” information available, only “just read what others did” kind of documentation.

@mrswats 2 ай бұрын

It's so funny that a Typing video is full of typos: P

@itachi2011100 2 ай бұрын

wouldn't like it any other way

@sgeisenh 2 ай бұрын

I'd be curious to hear your thoughts on how you expect/hope the type system evolves to _hopefully_ support concepts like proxy objects without the need for a plugin. Type annotations are definitely a big improvement when interacting with an existing codebase, but it still feels like a different language. The model I think of is TypeScript where there's reasonable support for type-level computations. But JS exposes far fewer implementation details, so it seems simpler to implement a type system that captures common forms of "dynamism" in JS. TS definitely has significant deficiencies (e.g. bivariant method arguments) but it seems like there may still be a lot of ideas that python could draw to be able to fully annotate a larger variety of constructs.

@anthonywritescode 2 ай бұрын

python has significantly more magic than js ever would have to deal with (descriptors, meta classes, etc.) such that I don't think the type system will (or even should!) represent every thing you can do. the only reason that I did make the proxy "work" is because it already existed. if the code were written with safety in mind such a pattern would not have been used

@sgeisenh 2 ай бұрын

@@anthonywritescode that makes sense. Type annotations do seem to encourage a safer subset of the language. Thanks for the reply!

@ChristianBrugger 2 ай бұрын

Thanks for that comment and adding that context. Good to know these tools are there, but better to design it, such that this is not needed 😂

@jrheard 2 ай бұрын

Love this, thanks Anthony!

@bswck 2 ай бұрын

there are various approaches for creating sentinels. the one with enum, but also `MISSING = type("_MISSING", (), {})()` or creating a custom class with the class keyword and then reusing a single instance of it is what I tend to use if I don't want `object()`. or even importing MISSING from dataclasses could work, but well. I'm not sure it's a good idea. everything depends whether you need concrete unions or a killer type "object" in a variable (or, more often, a parameter).

@anthonywritescode 2 ай бұрын

the enum approach is the only one I know that works well with mypy and narrowing

@antoniov845 14 күн бұрын

Class LazySingleton

@TheAulto 2 ай бұрын

he is back!

@kidhq 2 ай бұрын

For the singleton field `Lazy._inst`, my first idea would've just been to store `None` and type as `Optional[R]`. Is there a benefit to using the specific `empty` object with the _EmptyType enum instead? Related timestamp: 1:14 for creating empty object, 14:10 for updating with enum type

@anthonywritescode 2 ай бұрын

None, Ellipsis, etc. would have worked for most cases, though Django's implementation uses an explicit empty singleton

@kilianvounckx9904 2 ай бұрын

If, for some reason, your expensive function returns None, you wouldn't be able to store it if you also used is as the singleton field. You would check against None and the function would run always because it would refer to both the actual lazily computed object as the singleton. Using an empty object and the `is` operator takes care of this, because `is` compares by reference/address. This address is guaranteed to be the one of the singleton