Help: Convert rust error enums to python errors

[Shadow53]

I've been through the docs and guide a few times and I'm stuck figuring out how to go about this.

I have a library that should be usable in both Rust and Python, where Python support is feature-gated. The Rust library defines a bunch of error types as enums using thiserror, e.g.

#[derive(Debug, Error)]
pub enum SomeError {
    #[error("display impl: {0}")]
    VariantOne(#[source] AnotherError),
    #[error(...)]
    VariantTwo(usize),
    #[error(...)]
    VariantThree(#[source] AnotherError),
    #[error(...)]
    VariantFour(#[from] YetAnotherError),
}

What I'm struggling to wrap my head around is the best way to transform this error type into a Python exception.

1. pyclass fails because it is an enum and not a struct.
2. create_exception! creates a new type and does not modify an existing one.
3. impl_exception_boilerplate! seems closest, but conflicts with the implementation of std::error::Error from thiserror. If I modify the code to remove the use of thiserror (i.e. impl things myself), I get a new error that SomeError does not impl PyTypeInfo, which I am not comfortable trying to implement on my own.

Is there something I'm missing, or is this something that just isn't every doable in the current state of PyO3?

[davidhewitt]

If you want to use builtin Python exception types and be able to return Result<_, SomeError> from #[pymethods], impl From<SomeError> for PyErr might suit what you need?

If you want a custom exception type I would probably recommend #[pyclass(extends=PyException)] to make a separate error classe which the From impl would target.

[Shadow53]

I'm going with the second option for now.

After further searching, it looks like this is a (partial?) duplicate of #417, so I'll close this in favor of that.