Add support for SmallVec in conversion traits (#3440)

Cargo.toml

@@ -41,6 +41,7 @@ num-bigint = { version = "0.4", optional = true }
 num-complex = { version = ">= 0.2, < 0.5", optional = true }
 rust_decimal = { version = "1.0.0", default-features = false, optional = true }
 serde = { version = "1.0", optional = true }
+smallvec = { version = "1.11.1", optional = true }
 
 [dev-dependencies]
 assert_approx_eq = "1.1.0"
@@ -104,6 +105,7 @@ full = [
     "num-bigint",
     "num-complex",
     "hashbrown",
+    "smallvec",
     "serde",
     "indexmap",
     "eyre",

newsfragments/3507.added.md

@@ -0,0 +1 @@
+Add `smallvec` feature to add `ToPyObject`, `IntoPy` and `FromPyObject` implementations for `smallvec::SmallVec`.

src/conversions/mod.rs

@@ -9,4 +9,5 @@ pub mod num_bigint;
 pub mod num_complex;
 pub mod rust_decimal;
 pub mod serde;
+pub mod smallvec;
 mod std;

src/conversions/smallvec.rs

@@ -0,0 +1,118 @@
+#![cfg(feature = "smallvec")]
+
+//!  Conversions to and from [smallvec](https://docs.rs/smallvec/).
+//!
+//! # Setup
+//!
+//! To use this feature, add this to your **`Cargo.toml`**:
+//!
+//! ```toml
+//! [dependencies]
+//! # change * to the latest versions
+//! smallvec = "*"
+#![doc = concat!("pyo3 = { version = \"", env!("CARGO_PKG_VERSION"),  "\", features = [\"smallvec\"] }")]
+//! ```
+//!
+//! Note that you must use compatible versions of smallvec and PyO3.
+//! The required smallvec version may vary based on the version of PyO3.
+use crate::exceptions::PyTypeError;
+#[cfg(feature = "experimental-inspect")]
+use crate::inspect::types::TypeInfo;
+use crate::types::list::new_from_iter;
+use crate::types::{PySequence, PyString};
+use crate::{
+    ffi, FromPyObject, IntoPy, PyAny, PyDowncastError, PyObject, PyResult, Python, ToPyObject,
+};
+use smallvec::{Array, SmallVec};
+
+impl<A> ToPyObject for SmallVec<A>
+where
+    A: Array,
+    A::Item: ToPyObject,
+{
+    fn to_object(&self, py: Python<'_>) -> PyObject {
+        self.as_slice().to_object(py)
+    }
+}
+
+impl<A> IntoPy<PyObject> for SmallVec<A>
+where
+    A: Array,
+    A::Item: IntoPy<PyObject>,
+{
+    fn into_py(self, py: Python<'_>) -> PyObject {
+        let mut iter = self.into_iter().map(|e| e.into_py(py));
+        let list = new_from_iter(py, &mut iter);
+        list.into()
+    }
+
+    #[cfg(feature = "experimental-inspect")]
+    fn type_output() -> TypeInfo {
+        TypeInfo::list_of(A::Item::type_output())
+    }
+}
+
+impl<'a, A> FromPyObject<'a> for SmallVec<A>
+where
+    A: Array,
+    A::Item: FromPyObject<'a>,
+{
+    fn extract(obj: &'a PyAny) -> PyResult<Self> {
+        if obj.is_instance_of::<PyString>() {
+            return Err(PyTypeError::new_err("Can't extract `str` to `SmallVec`"));
+        }
+        extract_sequence(obj)
+    }
+
+    #[cfg(feature = "experimental-inspect")]
+    fn type_input() -> TypeInfo {
+        TypeInfo::sequence_of(A::type_input())
+    }
+}
+
+fn extract_sequence<'s, A>(obj: &'s PyAny) -> PyResult<SmallVec<A>>
+where
+    A: Array,
+    A::Item: FromPyObject<'s>,
+{
+    // Types that pass `PySequence_Check` usually implement enough of the sequence protocol
+    // to support this function and if not, we will only fail extraction safely.
+    let seq: &PySequence = unsafe {
+        if ffi::PySequence_Check(obj.as_ptr()) != 0 {
+            obj.downcast_unchecked()
+        } else {
+            return Err(PyDowncastError::new(obj, "Sequence").into());
+        }
+    };
+
+    let mut sv = SmallVec::with_capacity(seq.len().unwrap_or(0));
+    for item in seq.iter()? {
+        sv.push(item?.extract::<A::Item>()?);
+    }
+    Ok(sv)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::types::PyList;
+
+    #[test]
+    fn test_smallvec_into_py() {
+        Python::with_gil(|py| {
+            let sv: SmallVec<[u64; 8]> = [1, 2, 3, 4, 5].iter().cloned().collect();
+            let hso: PyObject = sv.clone().into_py(py);
+            let l = PyList::new(py, [1, 2, 3, 4, 5]);
+            assert!(l.eq(hso).unwrap());
+        });
+    }
+
+    #[test]
+    fn test_smallvec_from_py_object() {
+        Python::with_gil(|py| {
+            let l = PyList::new(py, [1, 2, 3, 4, 5]);
+            let sv: SmallVec<[u64; 8]> = l.extract().unwrap();
+            assert_eq!(sv.as_slice(), [1, 2, 3, 4, 5]);
+        });
+    }
+}