Add optional support for conversion from indexmap::IndexMap

.github/workflows/ci.yml

@@ -130,11 +130,13 @@ jobs:
         id: settings
         shell: bash
         run: |
-          echo "::set-output name=all_additive_features::macros num-bigint num-complex hashbrown serde multiple-pymethods"
+          echo "::set-output name=all_additive_features::macros num-bigint num-complex hashbrown indexmap serde multiple-pymethods"
 
       - if: matrix.msrv == 'MSRV'
         name: Prepare minimal package versions (MSRV only)
-        run: cargo update -p hashbrown --precise 0.9.1
+        run: |
+          cargo update -p indexmap --precise 1.6.2
+          cargo update -p hashbrown:0.11.2 --precise 0.9.1
 
       - name: Build docs
         run: cargo doc --no-deps --no-default-features --features "${{ steps.settings.outputs.all_additive_features }}"
@@ -229,7 +231,7 @@ jobs:
           profile: minimal
           components: llvm-tools-preview
       - run: cargo test --no-default-features --no-fail-fast
-      - run: cargo test --no-default-features --no-fail-fast --features "macros num-bigint num-complex hashbrown serde multiple-pymethods"
+      - run: cargo test --no-default-features --no-fail-fast --features "macros num-bigint num-complex hashbrown indexmap serde multiple-pymethods"
       - run: cargo test --manifest-path=pyo3-macros-backend/Cargo.toml
       - run: cargo test --manifest-path=pyo3-build-config/Cargo.toml
       # can't yet use actions-rs/grcov with source-based coverage: https://github.com/actions-rs/grcov/issues/105

.github/workflows/guide.yml

@@ -44,7 +44,7 @@ jobs:
         # This adds the docs to gh-pages-build/doc
       - name: Build the doc
         run: |
-          cargo +nightly rustdoc --lib --no-default-features --features="macros num-bigint num-complex hashbrown serde multiple-pymethods" -- --cfg docsrs
+          cargo +nightly rustdoc --lib --no-default-features --features="macros num-bigint num-complex hashbrown indexmap serde multiple-pymethods" -- --cfg docsrs
           cp -r target/doc gh-pages-build/doc
           echo "<meta http-equiv=refresh content=0;url=pyo3/index.html>" > gh-pages-build/doc/index.html
 

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- Add `indexmap` feature to add `ToPyObject`, `IntoPy` and `FromPyObject` implementations for `indexmap::IndexMap`. [#1728](https://github.com/PyO3/pyo3/pull/1728)
+
 ### Fixed
 
 - Fix regression in 0.14.0 rejecting usage of `#[doc(hidden)]` on structs and functions annotated with PyO3 macros. [#1722](https://github.com/PyO3/pyo3/pull/1722)

Cargo.toml

@@ -27,6 +27,7 @@ paste = { version = "0.1.18", optional = true }
 pyo3-macros = { path = "pyo3-macros", version = "=0.14.1", optional = true }
 unindent = { version = "0.1.4", optional = true }
 hashbrown = { version = ">= 0.9, < 0.12", optional = true }
+indexmap = { version = ">= 1.6, < 1.8", optional = true }
 serde = {version = "1.0", optional = true}
 
 [dev-dependencies]
@@ -117,5 +118,5 @@ members = [
 
 [package.metadata.docs.rs]
 no-default-features = true
-features = ["macros", "num-bigint", "num-complex", "hashbrown", "serde", "multiple-pymethods"]
+features = ["macros", "num-bigint", "num-complex", "hashbrown", "serde", "multiple-pymethods", "indexmap"]
 rustdoc-args = ["--cfg", "docsrs"]

guide/src/conversions/tables.md

@@ -20,7 +20,7 @@ The table below contains the Python type and the corresponding function argument
 | `float`       | `f32`, `f64`                    | `&PyFloat`           |
 | `complex`     | `num_complex::Complex`[^1]      | `&PyComplex`         |
 | `list[T]`     | `Vec<T>`                        | `&PyList`            |
-| `dict[K, V]`  | `HashMap<K, V>`, `BTreeMap<K, V>`, `hashbrown::HashMap<K, V>`[^2] | `&PyDict` |
+| `dict[K, V]`  | `HashMap<K, V>`, `BTreeMap<K, V>`, `hashbrown::HashMap<K, V>`[^2], `indexmap::IndexMap<K, V>`[^3] | `&PyDict` |
 | `tuple[T, U]` | `(T, U)`, `Vec<T>`              | `&PyTuple`           |
 | `set[T]`      | `HashSet<T>`, `BTreeSet<T>`, `hashbrown::HashSet<T>`[^2] | `&PySet` |
 | `frozenset[T]` | `HashSet<T>`, `BTreeSet<T>`, `hashbrown::HashSet<T>`[^2] | `&PyFrozenSet` |
@@ -94,3 +94,5 @@ Finally, the following Rust types are also able to convert to Python as return v
 [^1]: Requires the `num-complex` optional feature.
 
 [^2]: Requires the `hashbrown` optional feature.
+
+[^3]: Requires the `indexmap` optional feature.

src/conversions/indexmap.rs

@@ -0,0 +1,223 @@
+//!  Conversions to and from [indexmap](https://docs.rs/indexmap/)’s
+//! `IndexMap`.
+//!
+//! [`indexmap::IndexMap`] is a hash table that is closely compatible with the standard [`std::collections::HashMap`],
+//! with the difference that it preserves the insertion order when iterating over keys. It was inspired
+//! by Python's 3.6+ dict implementation.
+//!
+//! Dictionary order is guaranteed to be insertion order since Python 3.7, and the conversions with IndexMap will reflect
+//! that guarantee. In practice, the guarantee will also be mainted in Python 3.6 because of the implementation details
+//! of CPython and PyPy.
+//!
+//! # Setup
+//!
+//! To use this feature, add this to your **`Cargo.toml`**:
+//!
+//! ```toml
+//! [dependencies]
+//! # change * to the latest versions
+//! indexmap = "*"
+// workaround for `extended_key_value_attributes`: https://github.com/rust-lang/rust/issues/82768#issuecomment-803935643
+#![cfg_attr(docsrs, cfg_attr(docsrs, doc = concat!("pyo3 = { version = \"", env!("CARGO_PKG_VERSION"),  "\", features = [\"indexmap\"] }")))]
+#![cfg_attr(
+    not(docsrs),
+    doc = "pyo3 = { version = \"*\", features = [\"indexmap\"] }"
+)]
+//! ```
+//!
+//! Note that you must use compatible versions of indexmap and PyO3.
+//! The required indexmap version may vary based on the version of PyO3.
+//!
+//! # Examples
+//!
+//! Using [indexmap](https://docs.rs/indexmap) to return a dictionary with some statistics
+//! about a list of numbers. Because of the insertion order guarantees, the Python code will
+//! always print the same result, matching users' expectations about Python's dict.
+//!
+//! ```rust
+//! use indexmap::{indexmap, IndexMap};
+//! use pyo3::prelude::*;
+//!
+//! fn median(data: &Vec<i32>) -> f32 {
+//!     let sorted_data = data.clone().sort();
+//!     let mid = data.len() / 2;
+//!     if (data.len() % 2 == 0) {
+//!         data[mid] as f32
+//!     }
+//!     else {
+//!         (data[mid] + data[mid - 1]) as f32 / 2.0
+//!     }
+//! }
+//!
+//! fn mean(data: &Vec<i32>) -> f32 {
+//!     data.iter().sum::<i32>() as f32 / data.len() as f32
+//! }
+//! fn mode(data: &Vec<i32>) -> f32 {
+//!     let mut frequency = IndexMap::new(); // we can use IndexMap as any hash table
+//!
+//!     for &element in data {
+//!         *frequency.entry(element).or_insert(0) += 1;
+//!     }
+//!
+//!     frequency
+//!         .iter()
+//!         .max_by(|a, b| a.1.cmp(&b.1))
+//!         .map(|(k, _v)| *k)
+//!         .unwrap() as f32
+//!   }
+//!
+//! #[pyfunction]
+//! fn calculate_statistics(data: Vec<i32>) -> IndexMap<&'static str, f32> {
+//!     indexmap!{
+//!        "median" => median(&data),
+//!        "mean" => mean(&data),
+//!        "mode" => mode(&data),
+//!     }
+//! }
+//!
+//! #[pymodule]
+//! fn my_module(_py: Python, m: &PyModule) -> PyResult<()> {
+//!     m.add_function(wrap_pyfunction!(calculate_statistics, m)?)?;
+//!     Ok(())
+//! }
+//! ```
+//!
+//! Python code:
+//! ```python
+//! from my_module import calculate_statistics
+//!
+//! data = [1, 1, 1, 3, 4, 5]
+//! print(calculate_statistics(data))
+//! # always prints {"median": 2.0, "mean": 2.5, "mode": 1.0} in the same order
+//! # if another hash table was used, the order could be random
+//! ```
+
+mod indexmap_indexmap_conversion {
+
+    use crate::types::*;
+    use crate::{FromPyObject, IntoPy, PyErr, PyObject, PyTryFrom, Python, ToPyObject};
+    use std::{cmp, hash};
+
+    impl<K, V, H> ToPyObject for indexmap::IndexMap<K, V, H>
+    where
+        K: hash::Hash + cmp::Eq + ToPyObject,
+        V: ToPyObject,
+        H: hash::BuildHasher,
+    {
+        fn to_object(&self, py: Python) -> PyObject {
+            IntoPyDict::into_py_dict(self, py).into()
+        }
+    }
+
+    impl<K, V, H> IntoPy<PyObject> for indexmap::IndexMap<K, V, H>
+    where
+        K: hash::Hash + cmp::Eq + IntoPy<PyObject>,
+        V: IntoPy<PyObject>,
+        H: hash::BuildHasher,
+    {
+        fn into_py(self, py: Python) -> PyObject {
+            let iter = self
+                .into_iter()
+                .map(|(k, v)| (k.into_py(py), v.into_py(py)));
+            IntoPyDict::into_py_dict(iter, py).into()
+        }
+    }
+
+    impl<'source, K, V, S> FromPyObject<'source> for indexmap::IndexMap<K, V, S>
+    where
+        K: FromPyObject<'source> + cmp::Eq + hash::Hash,
+        V: FromPyObject<'source>,
+        S: hash::BuildHasher + Default,
+    {
+        fn extract(ob: &'source PyAny) -> Result<Self, PyErr> {
+            let dict = <PyDict as PyTryFrom>::try_from(ob)?;
+            let mut ret = indexmap::IndexMap::with_capacity_and_hasher(dict.len(), S::default());
+            for (k, v) in dict.iter() {
+                ret.insert(K::extract(k)?, V::extract(v)?);
+            }
+            Ok(ret)
+        }
+    }
+}
+
+#[cfg(test)]
+mod test_indexmap {
+
+    use crate::types::*;
+    use crate::{IntoPy, PyObject, PyTryFrom, Python, ToPyObject};
+
+    #[test]
+    fn test_indexmap_indexmap_to_python() {
+        Python::with_gil(|py| {
+            let mut map = indexmap::IndexMap::<i32, i32>::new();
+            map.insert(1, 1);
+
+            let m = map.to_object(py);
+            let py_map = <PyDict as PyTryFrom>::try_from(m.as_ref(py)).unwrap();
+
+            assert!(py_map.len() == 1);
+            assert!(py_map.get_item(1).unwrap().extract::<i32>().unwrap() == 1);
+            assert_eq!(
+                map,
+                py_map.extract::<indexmap::IndexMap::<i32, i32>>().unwrap()
+            );
+        });
+    }
+
+    #[test]
+    fn test_indexmap_indexmap_into_python() {
+        Python::with_gil(|py| {
+            let mut map = indexmap::IndexMap::<i32, i32>::new();
+            map.insert(1, 1);
+
+            let m: PyObject = map.into_py(py);
+            let py_map = <PyDict as PyTryFrom>::try_from(m.as_ref(py)).unwrap();
+
+            assert!(py_map.len() == 1);
+            assert!(py_map.get_item(1).unwrap().extract::<i32>().unwrap() == 1);
+        });
+    }
+
+    #[test]
+    fn test_indexmap_indexmap_into_dict() {
+        Python::with_gil(|py| {
+            let mut map = indexmap::IndexMap::<i32, i32>::new();
+            map.insert(1, 1);
+
+            let py_map = map.into_py_dict(py);
+
+            assert_eq!(py_map.len(), 1);
+            assert_eq!(py_map.get_item(1).unwrap().extract::<i32>().unwrap(), 1);
+        });
+    }
+
+    #[test]
+    fn test_indexmap_indexmap_insertion_order_round_trip() {
+        Python::with_gil(|py| {
+            let n = 20;
+            let mut map = indexmap::IndexMap::<i32, i32>::new();
+
+            for i in 1..=n {
+                if i % 2 == 1 {
+                    map.insert(i, i);
+                } else {
+                    map.insert(n - i, i);
+                }
+            }
+
+            let py_map = map.clone().into_py_dict(py);
+
+            let trip_map = py_map.extract::<indexmap::IndexMap<i32, i32>>().unwrap();
+
+            for (((k1, v1), (k2, v2)), (k3, v3)) in
+                map.iter().zip(py_map.iter()).zip(trip_map.iter())
+            {
+                let k2 = k2.extract::<i32>().unwrap();
+                let v2 = v2.extract::<i32>().unwrap();
+                assert_eq!((k1, v1), (&k2, &v2));
+                assert_eq!((k1, v1), (k3, v3));
+                assert_eq!((&k2, &v2), (k3, v3));
+            }
+        });
+    }
+}

src/conversions/mod.rs

@@ -1,5 +1,8 @@
 //! This module contains conversions between various Rust object and their representation in Python.
 
 mod array;
+#[cfg(feature = "indexmap")]
+#[cfg_attr(docsrs, doc(cfg(feature = "indexmap")))]
+mod indexmap;
 mod osstr;
 mod path;

src/lib.rs

@@ -74,6 +74,10 @@
 //! [`HashMap`](https://docs.rs/hashbrown/latest/hashbrown/struct.HashMap.html) and
 //! [`HashSet`](https://docs.rs/hashbrown/latest/hashbrown/struct.HashSet.html) types.
 //
+//! - `indexmap`: Enables conversions between Python dictionary and
+//! [indexmap](https://docs.rs/indexmap)'s
+//! [`IndexMap`](https://docs.rs/indexmap/latest/indexmap/map/struct.IndexMap.html).
+//
 //! - `multiple-pymethods`: Enables the use of multiple
 //! [`#[pymethods]`](crate::proc_macro::pymethods) blocks per
 //! [`#[pyclass]`](crate::proc_macro::pyclass). This adds a dependency on the