add conversion support for either::Either

Cargo.toml

@@ -37,6 +37,7 @@ futures-util = "0.3"
 # crate integrations that can be added using the eponymous features
 anyhow = { version = "1.0", optional = true }
 chrono = { version = "0.4.25", default-features = false, optional = true }
+either = { version = "1.9", optional = true }
 eyre = { version = ">= 0.4, < 0.7", optional = true }
 hashbrown = { version = ">= 0.9, < 0.15", optional = true }
 indexmap = { version = ">= 1.6, < 3", optional = true }
@@ -111,6 +112,7 @@ full = [
     "smallvec",
     "serde",
     "indexmap",
+    "either",
     "eyre",
     "anyhow",
     "experimental-inspect",
@@ -129,7 +131,7 @@ members = [
 
 [package.metadata.docs.rs]
 no-default-features = true
-features = ["macros", "num-bigint", "num-complex", "hashbrown", "serde", "multiple-pymethods", "indexmap", "eyre", "chrono", "rust_decimal"]
+features = ["macros", "num-bigint", "num-complex", "hashbrown", "serde", "multiple-pymethods", "indexmap", "eyre", "either", "chrono", "rust_decimal"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [workspace.lints.clippy]

guide/src/features.md

@@ -109,6 +109,10 @@ Adds a dependency on [chrono](https://docs.rs/chrono). Enables a conversion from
 - [NaiveTime](https://docs.rs/chrono/latest/chrono/naive/struct.NaiveTime.html) -> [`PyTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyTime.html)
 - [DateTime](https://docs.rs/chrono/latest/chrono/struct.DateTime.html) -> [`PyDateTime`]({{#PYO3_DOCS_URL}}/pyo3/types/struct.PyDateTime.html)
 
+### `either`
+
+Adds a dependency on [either](https://docs.rs/either). Enables a conversions into [either](https://docs.rs/either)’s [`Either`](https://docs.rs/either/latest/either/struct.Report.html) type.
+
 ### `eyre`
 
 Adds a dependency on [eyre](https://docs.rs/eyre). Enables a conversion from [eyre](https://docs.rs/eyre)’s [`Report`](https://docs.rs/eyre/latest/eyre/struct.Report.html) type to [`PyErr`]({{#PYO3_DOCS_URL}}/pyo3/struct.PyErr.html), for easy error handling.

newsfragments/3456.added.md

@@ -0,0 +1 @@
+Add optional conversion support for `either::Either<L, R>` sum type (under "either" feature).

src/conversions/either.rs

@@ -0,0 +1,146 @@
+#![cfg(feature = "either")]
+
+//! Conversion to/from
+//! [either](https://docs.rs/either/ "A library for easy idiomatic error handling and reporting in Rust applications")’s
+//! [`Either`] type to a union of two Python types.
+//!
+//! Use of a generic sum type like [either] is common when you want to either accept one of two possible
+//! types as an argument or return one of two possible types from a function, without having to define
+//! a helper type manually yourself.
+//!
+//! # Setup
+//!
+//! To use this feature, add this to your **`Cargo.toml`**:
+//!
+//! ```toml
+//! [dependencies]
+//! ## change * to the version you want to use, ideally the latest.
+//! either = "*"
+#![doc = concat!("pyo3 = { version = \"", env!("CARGO_PKG_VERSION"),  "\", features = [\"either\"] }")]
+//! ```
+//!
+//! Note that you must use compatible versions of either and PyO3.
+//! The required either version may vary based on the version of PyO3.
+//!
+//! # Example: Convert a `int | str` to `Either<i32, String>`.
+//!
+//! ```rust
+//! use either::Either;
+//! use pyo3::{Python, ToPyObject};
+//!
+//! fn main() {
+//!     pyo3::prepare_freethreaded_python();
+//!     Python::with_gil(|py| {
+//!         // Create a string and an int in Python.
+//!         let py_str = "crab".to_object(py);
+//!         let py_int = 42.to_object(py);
+//!         // Now convert it to an Either<i32, String>.
+//!         let either_str: Either<i32, String> = py_str.extract(py).unwrap();
+//!         let either_int: Either<i32, String> = py_int.extract(py).unwrap();
+//!     });
+//! }
+//! ```
+//!
+//! [either](https://docs.rs/either/ "A library for easy idiomatic error handling and reporting in Rust applications")’s
+
+use crate::{
+    exceptions::PyTypeError, inspect::types::TypeInfo, FromPyObject, IntoPy, PyAny, PyObject,
+    PyResult, Python, ToPyObject,
+};
+use either::Either;
+
+#[cfg_attr(docsrs, doc(cfg(feature = "either")))]
+impl<L, R> IntoPy<PyObject> for Either<L, R>
+where
+    L: IntoPy<PyObject>,
+    R: IntoPy<PyObject>,
+{
+    #[inline]
+    fn into_py(self, py: Python<'_>) -> PyObject {
+        match self {
+            Either::Left(l) => l.into_py(py),
+            Either::Right(r) => r.into_py(py),
+        }
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "either")))]
+impl<L, R> ToPyObject for Either<L, R>
+where
+    L: ToPyObject,
+    R: ToPyObject,
+{
+    #[inline]
+    fn to_object(&self, py: Python<'_>) -> PyObject {
+        match self {
+            Either::Left(l) => l.to_object(py),
+            Either::Right(r) => r.to_object(py),
+        }
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "either")))]
+impl<'source, L, R> FromPyObject<'source> for Either<L, R>
+where
+    L: FromPyObject<'source>,
+    R: FromPyObject<'source>,
+{
+    #[inline]
+    fn extract(obj: &'source PyAny) -> PyResult<Self> {
+        if let Ok(l) = obj.extract::<L>() {
+            Ok(Either::Left(l))
+        } else if let Ok(r) = obj.extract::<R>() {
+            Ok(Either::Right(r))
+        } else {
+            let err_msg = format!("failed to convert the value to '{}'", Self::type_input());
+            Err(PyTypeError::new_err(err_msg))
+        }
+    }
+
+    fn type_input() -> TypeInfo {
+        TypeInfo::union_of(&[L::type_input(), R::type_input()])
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::exceptions::PyTypeError;
+    use crate::{Python, ToPyObject};
+
+    use either::Either;
+
+    #[test]
+    fn test_either_conversion() {
+        type E = Either<i32, String>;
+        type E1 = Either<i32, f32>;
+        type E2 = Either<f32, i32>;
+
+        Python::with_gil(|py| {
+            let l = E::Left(42);
+            let obj_l = l.to_object(py);
+            assert_eq!(obj_l.extract::<i32>(py).unwrap(), 42);
+            assert_eq!(obj_l.extract::<E>(py).unwrap(), l);
+
+            let r = E::Right("foo".to_owned());
+            let obj_r = r.to_object(py);
+            assert_eq!(obj_r.extract::<&str>(py).unwrap(), "foo");
+            assert_eq!(obj_r.extract::<E>(py).unwrap(), r);
+
+            let obj_s = "foo".to_object(py);
+            let err = obj_s.extract::<E1>(py).unwrap_err();
+            assert!(err.is_instance_of::<PyTypeError>(py));
+            assert_eq!(
+                err.to_string(),
+                "TypeError: failed to convert the value to 'Union[int, float]'"
+            );
+
+            let obj_i = 42.to_object(py);
+            assert_eq!(obj_i.extract::<E1>(py).unwrap(), E1::Left(42));
+            assert_eq!(obj_i.extract::<E2>(py).unwrap(), E2::Left(42.0));
+
+            let obj_f = 42.0.to_object(py);
+            assert_eq!(obj_f.extract::<E1>(py).unwrap(), E1::Right(42.0));
+            assert_eq!(obj_f.extract::<E2>(py).unwrap(), E2::Left(42.0));
+        });
+    }
+}

src/conversions/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod anyhow;
 pub mod chrono;
+pub mod either;
 pub mod eyre;
 pub mod hashbrown;
 pub mod indexmap;

src/lib.rs

@@ -82,6 +82,7 @@
 //! The following features enable interactions with other crates in the Rust ecosystem:
 //! - [`anyhow`]: Enables a conversion from [anyhow]’s [`Error`][anyhow_error] type to [`PyErr`].
 //! - [`chrono`]: Enables a conversion from [chrono]'s structures to the equivalent Python ones.
+//! - [`either`]: Enables conversions between Python objects and [either]'s [`Either`] type.
 //! - [`eyre`]: Enables a conversion from [eyre]’s [`Report`] type to [`PyErr`].
 //! - [`hashbrown`]: Enables conversions between Python objects and [hashbrown]'s [`HashMap`] and
 //! [`HashSet`] types.
@@ -257,6 +258,9 @@
 //! [`Serialize`]: https://docs.rs/serde/latest/serde/trait.Serialize.html
 //! [chrono]: https://docs.rs/chrono/ "Date and Time for Rust."
 //! [`chrono`]: ./chrono/index.html "Documentation about the `chrono` feature."
+//! [either]: https://docs.rs/either/ "A type that represents one of two alternatives."
+//! [`either`]: ./either/index.html "Documentation about the `either` feature."
+//! [`Either`]: https://docs.rs/either/latest/either/enum.Either.html
 //! [eyre]: https://docs.rs/eyre/ "A library for easy idiomatic error handling and reporting in Rust applications."
 //! [`Report`]: https://docs.rs/eyre/latest/eyre/struct.Report.html
 //! [`eyre`]: ./eyre/index.html "Documentation about the `eyre` feature."