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flask-msgspec

msgspec integration for Flask

This project was inspired by the flask-pydantic package created by bauerji and the Litestar framework, however while the validate decorator appears similar to the one found in flask-pydantic there are many differences.

Installation

pip install flask-msgspec

Usage

Consider this simple example:

class BodyStructWithConstraints(msgspec.Struct):
    foo: Annotated[int, msgspec.Meta(gt=0, le=100)]
    bar: Annotated[list[str | int], msgspec.Meta(min_length=1)]


@app.post(rule="/test/<uuid:uuid_value>")
@validate()
def test_handler(
    uuid_value: UUID,
    query1: float,
    body: BodyStructWithConstraints,
    optional_query: str = "default_value",
) -> dict:
    return locals()

Here we have a UUID path parameter, a required query parameter of float type, a body of type BodyStructWithConstraints, and an optional query parameter which is a string, the endpoint will return a dictionary of unknown types.

Currently there is only one reserved keyword; body. This tries to convert either request.data or request.form to the specified type.

Similar to how Litestar works, keywords that are neither path parameters or reserved keywords are considered query parameters.

The return type can be set either:

  • via the return_model keyword in validate decorator, or
  • by annotating the function return type. (return_model keyword takes priority)

Sequences/iterables can also be used for return type, e.g.; list[ResponseModel].

The successful response status code can also be changed in two ways:

  • via setting the status_code keyword in validate decorator, or
  • by using the standard Flask syntax of returning a tuple.

Returning a tuple with a status code will override the value set by the status_code keyword.

As you might have noticed mixing these together most likely will cause issues or just going to be annoying to annotate.
Avoid using the standard Flask tuple return syntax to change the status code if you are also using the function return type to annotate the return model. This will cause issues; first with a static type checker, then with the code handling return values and conversion.
In my opinion the response model should be set via annotating the return type of the function and if the status code needs to be changed use the status_code keyword. Additionally, if you need to set headers, then set both, the return type and status code using the keywords of the validate decorator.

You can use msgspec.Struct, dataclass, and most built-in types natively supported by msgspec.

More examples and others stuff will be added soon:tm:.