From d7c1a2906aee942e311c0155cefea4f1a5891fe4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ivan=20=E2=80=9CCLOVIS=E2=80=9D=20Canet?=
 <ivan.canet@gmail.com>
Date: Fri, 1 Jul 2022 13:05:39 +0200
Subject: [PATCH] IntoPy and FromPyObject allow the retrieval of the type
 information

---
 CHANGELOG.md                   |  2 ++
 src/conversion.rs              | 23 +++++++++++++++++++++++
 tests/ui/missing_intopy.stderr |  3 +++
 3 files changed, 28 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06fe05f7..c611c8d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Added `type_input()` and `type_output()` to get the Python type of any Python-compatible object. [#2490](https://github.com/PyO3/pyo3/pull/2490)
+
 ### Removed
 
 - Remove the deprecated `pyproto` feature, `#[pyproto]` macro, and all accompanying APIs. [#2587](https://github.com/PyO3/pyo3/pull/2587)
diff --git a/src/conversion.rs b/src/conversion.rs
index 29119928..05633076 100644
--- a/src/conversion.rs
+++ b/src/conversion.rs
@@ -2,6 +2,7 @@
 
 //! Defines conversions between Rust and Python types.
 use crate::err::{self, PyDowncastError, PyResult};
+use crate::inspect::types::TypeInfo;
 use crate::pyclass::boolean_struct::False;
 use crate::type_object::PyTypeInfo;
 use crate::types::PyTuple;
@@ -244,6 +245,17 @@ impl<T> ToBorrowedObject for T where T: ToPyObject {}
 pub trait IntoPy<T>: Sized {
     /// Performs the conversion.
     fn into_py(self, py: Python<'_>) -> T;
+
+    /// Extracts the type hint information for this type when it appears as a return value.
+    ///
+    /// For example, `Vec<u32>` would return `List[int]`.
+    /// The default implementation returns `Any`, which is correct for any type.
+    ///
+    /// For most types, the return value for this method will be identical to that of [`FromPyObject::type_input`].
+    /// It may be different for some types, such as `Dict`, to allow duck-typing: functions return `Dict` but take `Mapping` as argument.
+    fn type_output() -> TypeInfo {
+        TypeInfo::Any
+    }
 }
 
 /// Extract a type from a Python object.
@@ -289,6 +301,17 @@ pub trait IntoPy<T>: Sized {
 pub trait FromPyObject<'source>: Sized {
     /// Extracts `Self` from the source `PyObject`.
     fn extract(ob: &'source PyAny) -> PyResult<Self>;
+
+    /// Extracts the type hint information for this type when it appears as an argument.
+    ///
+    /// For example, `Vec<u32>` would return `Sequence[int]`.
+    /// The default implementation returns `Any`, which is correct for any type.
+    ///
+    /// For most types, the return value for this method will be identical to that of [`IntoPy::type_output`].
+    /// It may be different for some types, such as `Dict`, to allow duck-typing: functions return `Dict` but take `Mapping` as argument.
+    fn type_input() -> TypeInfo {
+        TypeInfo::Any
+    }
 }
 
 /// Identity conversion: allows using existing `PyObject` instances where
diff --git a/tests/ui/missing_intopy.stderr b/tests/ui/missing_intopy.stderr
index 2419ef60..493f3e61 100644
--- a/tests/ui/missing_intopy.stderr
+++ b/tests/ui/missing_intopy.stderr
@@ -20,6 +20,9 @@ note: the following trait must be implemented
     | / pub trait IntoPy<T>: Sized {
     | |     /// Performs the conversion.
     | |     fn into_py(self, py: Python<'_>) -> T;
+    | |
+...   |
+    | |     }
     | | }
     | |_^
     = note: this error originates in the attribute macro `pyo3::pyfunction` (in Nightly builds, run with -Z macro-backtrace for more info)