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0 pointsLtWorf24d ago0 comments

They can be used at runtime though. I wrote typedload, to load external data (json/bson/yaml) into python typed objects. In this way you know that if the data doesn't match the expectations you will have an exception at a specific point in the code, and after that it's safe to use the objects, rather than having to manually check at every access.

Now there are several other libraries that do this thing, but at the time (python3.5 and 3.6) it was the only option.

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yunnpp24d ago

That seems to handle deserialization? But would it protect you from assigning a value of the wrong type to the object later on?

maleldil23d ago

That depends on what you're using. If you're using Pydantic, which lets you define a struct-like data type with validation, you can tell it to validate assignments as well [1]. Or you can set the class as frozen and forbid assignment entirely [2].

However, if you mean annotating a local variable with a type, then no, nothing will stop it at runtime. If you use a type checker, though, it will tell you that statically.

The ecosystem also offers other runtime validation options, such as beartype [3]. For example, you can annotate a function such that it always checks the data types of input parameters when called. You can even apply this to a whole module if you want, but I don't think that's commonly done.

[1] https://docs.pydantic.dev/latest/api/config/#pydantic.config...

[2] https://docs.pydantic.dev/latest/api/config/#pydantic.config...

[3] https://beartype.readthedocs.io/en/latest/eli5/

LtWorfOP23d ago

Checking types on all function calls adds a considerable amount of extra work that I personally am not willing to pay, especially since static type checkers exist.

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LtWorfOP24d ago

It must be used in combination with a static checker to be useful.

So you can do like a = typedload.load(json_data, int) and then "a" is considered to be an int and at runtime will be an int.

Of course your static checker should prevent you from doing a + "string" later on because that would fail.

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