Add dataclass and pydantic support with simplified implementation

.github/workflows/rust.yml

@@ -80,6 +80,12 @@ jobs:
 
   test:
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        pydantic: [true, false]
+        abi3: [true, false]
+    name: Test (pydantic=${{ matrix.pydantic }}, abi3=${{ matrix.abi3 }})
     steps:
       - name: Checkout
         uses: actions/checkout@v5
@@ -94,16 +100,15 @@ jobs:
       - name: Cache dependencies
         uses: Swatinem/rust-cache@v2
 
-      - name: Run tests
-        uses: actions-rs/cargo@v1
-        with:
-          command: test
+      - name: Install pydantic
+        if: matrix.pydantic
+        run: pip install pydantic
 
-      - name: Run tests with abi3 feature
+      - name: Run tests
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --features abi3-py38
+          args: ${{ matrix.abi3 && '--features pyo3/abi3' || '' }}
 
   semver-check:
     runs-on: ubuntu-latest

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "serde-pyobject"
-version = "0.7.1"
+version = "0.8.0"
 edition = "2021"
 
 description = "PyO3's PyAny as a serde data format"
@@ -10,14 +10,12 @@ keywords = ["serde", "pyo3", "python", "ffi"]
 license = "MIT OR Apache-2.0"
 
 [dependencies]
-pyo3 = ">=0.26.0"
+log = "0.4.28"
+pyo3 = ">=0.27.0"
 serde = "1.0.228"
 
 [dev-dependencies]
 maplit = "1.0.2"
-pyo3 = { version = ">=0.26.0", features = ["auto-initialize"] }
+pyo3 = { version = "0.27.0", features = ["auto-initialize"] }
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.145"
-
-[features]
-abi3-py38 = ["pyo3/abi3-py38"]

src/dataclass.rs

@@ -0,0 +1,20 @@
+use pyo3::{types::*, Bound, PyResult, Python};
+
+/// Check if the given object is an instance of a dataclass by `dataclasses.is_dataclass`,
+/// and convert it to a PyDict using `dataclasses.asdict`.
+pub fn dataclass_as_dict<'py>(
+    py: Python<'py>,
+    obj: &Bound<'py, PyAny>,
+) -> PyResult<Option<Bound<'py, PyDict>>> {
+    let module = PyModule::import(py, "dataclasses")?;
+    let is_dataclass_fn = module.getattr("is_dataclass")?;
+
+    if is_dataclass_fn.call1((obj,))?.extract::<bool>()? {
+        let asdict_fn = module.getattr("asdict")?;
+        let dict_obj = asdict_fn.call1((obj,))?;
+        let dict = dict_obj.cast_into::<PyDict>()?;
+        Ok(Some(dict))
+    } else {
+        Ok(None)
+    }
+}

src/de.rs

@@ -1,4 +1,8 @@
-use crate::error::{Error, Result};
+use crate::{
+    dataclass::dataclass_as_dict,
+    error::{Error, Result},
+    pydantic::pydantic_model_as_dict,
+};
 use pyo3::{types::*, Bound};
 use serde::{
     de::{self, value::StrDeserializer, MapAccess, SeqAccess, Visitor},
@@ -307,13 +311,13 @@ impl<'de> de::Deserializer<'de> for PyAnyDeserializer<'_> {
         V: Visitor<'de>,
     {
         if self.0.is_instance_of::<PyDict>() {
-            return visitor.visit_map(MapDeserializer::new(self.0.downcast()?));
+            return visitor.visit_map(MapDeserializer::new(self.0.cast()?));
         }
         if self.0.is_instance_of::<PyList>() {
-            return visitor.visit_seq(SeqDeserializer::from_list(self.0.downcast()?));
+            return visitor.visit_seq(SeqDeserializer::from_list(self.0.cast()?));
         }
         if self.0.is_instance_of::<PyTuple>() {
-            return visitor.visit_seq(SeqDeserializer::from_tuple(self.0.downcast()?));
+            return visitor.visit_seq(SeqDeserializer::from_tuple(self.0.cast()?));
         }
         if self.0.is_instance_of::<PyString>() {
             return visitor.visit_str(&self.0.extract::<String>()?);
@@ -328,10 +332,14 @@ impl<'de> de::Deserializer<'de> for PyAnyDeserializer<'_> {
         if self.0.is_instance_of::<PyFloat>() {
             return visitor.visit_f64(self.0.extract()?);
         }
+        if let Some(dict) = dataclass_as_dict(self.0.py(), &self.0)? {
+            return visitor.visit_map(MapDeserializer::new(&dict));
+        }
+        if let Some(dict) = pydantic_model_as_dict(self.0.py(), &self.0)? {
+            return visitor.visit_map(MapDeserializer::new(&dict));
+        }
         if self.0.hasattr("__dict__")? {
-            return visitor.visit_map(MapDeserializer::new(
-                self.0.getattr("__dict__")?.downcast()?,
-            ));
+            return visitor.visit_map(MapDeserializer::new(self.0.getattr("__dict__")?.cast()?));
         }
         if self.0.hasattr("__slots__")? {
             // __slots__ and __dict__ are mutually exclusive, see
@@ -353,9 +361,9 @@ impl<'de> de::Deserializer<'de> for PyAnyDeserializer<'_> {
     ) -> Result<V::Value> {
         // Nested dict `{ "A": { "a": 1, "b": 2 } }` is deserialized as `A { a: 1, b: 2 }`
         if self.0.is_instance_of::<PyDict>() {
-            let dict: &Bound<PyDict> = self.0.downcast()?;
+            let dict: &Bound<PyDict> = self.0.cast()?;
             if let Some(inner) = dict.get_item(name)? {
-                if let Ok(inner) = inner.downcast() {
+                if let Ok(inner) = inner.cast() {
                     return visitor.visit_map(MapDeserializer::new(inner));
                 }
             }
@@ -418,7 +426,7 @@ impl<'de> de::Deserializer<'de> for PyAnyDeserializer<'_> {
             });
         }
         if self.0.is_instance_of::<PyDict>() {
-            let dict: &Bound<PyDict> = self.0.downcast()?;
+            let dict: &Bound<PyDict> = self.0.cast()?;
             if dict.len() == 1 {
                 let key = dict.keys().get_item(0).unwrap();
                 let value = dict.values().get_item(0).unwrap();
@@ -441,10 +449,10 @@ impl<'de> de::Deserializer<'de> for PyAnyDeserializer<'_> {
         visitor: V,
     ) -> Result<V::Value> {
         if self.0.is_instance_of::<PyDict>() {
-            let dict: &Bound<PyDict> = self.0.downcast()?;
+            let dict: &Bound<PyDict> = self.0.cast()?;
             if let Some(value) = dict.get_item(name)? {
                 if value.is_instance_of::<PyTuple>() {
-                    let tuple: &Bound<PyTuple> = value.downcast()?;
+                    let tuple: &Bound<PyTuple> = value.cast()?;
                     return visitor.visit_seq(SeqDeserializer::from_tuple(tuple));
                 }
             }

src/error.rs

@@ -1,4 +1,4 @@
-use pyo3::{exceptions::PyRuntimeError, DowncastError, PyErr};
+use pyo3::{exceptions::PyRuntimeError, CastError, PyErr};
 use serde::{de, ser};
 use std::fmt::{self, Display};
 
@@ -12,8 +12,8 @@ impl From<PyErr> for Error {
     }
 }
 
-impl From<DowncastError<'_, '_>> for Error {
-    fn from(err: DowncastError) -> Self {
+impl From<CastError<'_, '_>> for Error {
+    fn from(err: CastError) -> Self {
         let err: PyErr = err.into();
         Error(err)
     }

src/lib.rs

@@ -4,8 +4,10 @@
 //! to Python objects.
 //!
 
+mod dataclass;
 mod de;
 mod error;
+mod pydantic;
 mod pylit;
 mod ser;
 

src/pydantic.rs

@@ -0,0 +1,31 @@
+use pyo3::{types::*, Bound, PyResult, Python};
+
+/// Check if the given object is an instance of pydantic BaseModel,
+/// and convert it to a PyDict using `model_dump()`.
+///
+/// If pydantic is not installed, this function returns Ok(None).
+pub fn pydantic_model_as_dict<'py>(
+    py: Python<'py>,
+    obj: &Bound<'py, PyAny>,
+) -> PyResult<Option<Bound<'py, PyDict>>> {
+    // Try to import pydantic module
+    let module = match PyModule::import(py, "pydantic") {
+        Ok(m) => m,
+        Err(_) => {
+            // If pydantic import fails for any reason, return None
+            log::debug!("pydantic module not found; skipping pydantic model check");
+            return Ok(None);
+        }
+    };
+
+    let base_model = module.getattr("BaseModel")?.cast_into::<PyType>()?;
+
+    if obj.is_instance(&base_model)? {
+        let model_dump_fn = obj.getattr("model_dump")?;
+        let dict_obj = model_dump_fn.call0()?;
+        let dict = dict_obj.cast_into::<PyDict>()?;
+        Ok(Some(dict))
+    } else {
+        Ok(None)
+    }
+}

tests/check_revertible.rs

@@ -1,5 +1,34 @@
+//! Roundtrip Conversion Tests (Rust → Python → Rust)
+//!
+//! This test suite verifies that Rust values can be converted to Python and back without
+//! data loss. Each test performs the following one-way roundtrip:
+//!
+//! 1. **Start**: Create a Rust value
+//! 2. **Serialize**: Rust value → Python object (via `to_pyobject`)
+//! 3. **Deserialize**: Python object → Rust value (via `from_pyobject`)
+//! 4. **Assert**: The deserialized Rust value equals the original Rust value
+//!
+//! **Note**: These tests do NOT verify the reverse direction (Python → Rust → Python).
+//! For tests that start with Python objects, see `python_custom_class.rs`, `python_dataclass.rs`,
+//! and `python_pydantic.rs`.
+//!
+//! This ensures that Rust data structures can safely cross the FFI boundary and return
+//! to Rust without corruption, which is essential for round-trip serialization scenarios.
+//!
+//! Coverage includes:
+//! - Primitive types (integers, floats, booleans, strings)
+//! - Collections (vectors, maps)
+//! - Structured data (structs, tuples, newtypes)
+//! - Enums (unit, newtype, tuple, and struct variants)
+//! - Option types
+//!
+//! For tests specific to Python types, see:
+//! - `python_custom_class.rs` - Custom Python classes with `__dict__`
+//! - `python_dataclass.rs` - Python dataclasses (standard library)
+//! - `python_pydantic.rs` - Pydantic models (requires `pydantic_support` feature)
+
 use maplit::hashmap;
-use pyo3::{ffi::c_str, prelude::*};
+use pyo3::prelude::*;
 use serde::{Deserialize, Serialize};
 use serde_pyobject::{from_pyobject, to_pyobject};
 
@@ -133,50 +162,3 @@ fn struct_variant() {
         b: 30,
     });
 }
-
-#[test]
-fn check_python_object() {
-    #[derive(Debug, PartialEq, Serialize, Deserialize)]
-    struct MyClass {
-        name: String,
-        age: i32,
-    }
-
-    Python::attach(|py| {
-        // Create an instance of Python object
-        py.run(
-            c_str!(
-                r#"
-class MyClass:
-    def __init__(self, name: str, age: int):
-        self.name = name
-        self.age = age
-        "#
-            ),
-            None,
-            None,
-        )
-        .unwrap();
-        // Create an instance of MyClass
-        let my_python_class = py
-            .eval(
-                c_str!(
-                    r#"
-MyClass("John", 30)
-"#
-                ),
-                None,
-                None,
-            )
-            .unwrap();
-
-        let my_rust_class = MyClass {
-            name: "John".to_string(),
-            age: 30,
-        };
-        let any: Bound<'_, PyAny> = to_pyobject(py, &my_rust_class).unwrap();
-        let rust_version: MyClass = from_pyobject(my_python_class).unwrap();
-        let python_version: MyClass = from_pyobject(any).unwrap();
-        assert_eq!(rust_version, python_version);
-    })
-}

tests/python_custom_class.rs

@@ -0,0 +1,68 @@
+//! Custom Python Class Tests (Python → Rust)
+//!
+//! This test suite verifies deserialization support for custom Python classes
+//! that use the `__dict__` attribute to store instance data.
+//!
+//! These are user-defined Python classes created with the `class` keyword and
+//! `__init__` method, which is the most basic and common way to define classes
+//! in Python.
+//!
+//! Each test:
+//! 1. Defines a Python class with `__init__` method
+//! 2. Creates an instance of that class
+//! 3. Deserializes the Python object to a Rust struct via `from_pyobject`
+//! 4. Verifies correctness by comparing with a Rust-originated value
+//!
+//! This ensures that basic Python objects can be seamlessly deserialized into
+//! Rust structures, enabling interoperability with user-defined Python types.
+
+use pyo3::{ffi::c_str, prelude::*};
+use serde::{Deserialize, Serialize};
+use serde_pyobject::{from_pyobject, to_pyobject};
+
+#[test]
+fn check_python_object() {
+    #[derive(Debug, PartialEq, Serialize, Deserialize)]
+    struct MyClass {
+        name: String,
+        age: i32,
+    }
+
+    Python::attach(|py| {
+        // Create an instance of Python object
+        py.run(
+            c_str!(
+                r#"
+class MyClass:
+    def __init__(self, name: str, age: int):
+        self.name = name
+        self.age = age
+        "#
+            ),
+            None,
+            None,
+        )
+        .unwrap();
+        // Create an instance of MyClass
+        let my_python_class = py
+            .eval(
+                c_str!(
+                    r#"
+MyClass("John", 30)
+"#
+                ),
+                None,
+                None,
+            )
+            .unwrap();
+
+        let my_rust_class = MyClass {
+            name: "John".to_string(),
+            age: 30,
+        };
+        let any: Bound<'_, PyAny> = to_pyobject(py, &my_rust_class).unwrap();
+        let rust_version: MyClass = from_pyobject(my_python_class).unwrap();
+        let python_version: MyClass = from_pyobject(any).unwrap();
+        assert_eq!(rust_version, python_version);
+    })
+}