deprecate `PyTryFrom` and `PyTryInto`

guide/src/migration.md

@@ -16,6 +16,7 @@ To migrate, switch all type casts to use `obj.downcast()` instead of `try_from(o
 Before:
 
 ```rust
+# #![allow(deprecated)]
 # use pyo3::prelude::*;
 # use pyo3::types::{PyInt, PyList};
 # fn main() -> PyResult<()> {

newsfragments/3601.changed.md

@@ -0,0 +1 @@
+Deprecate `PyTryFrom` and `PyTryInto` traits in favor of `any.downcast()` via the `PyTypeCheck` and `PyTypeInfo` traits.

src/conversion.rs

@@ -355,11 +355,20 @@ where
 /// If `T` implements `PyTryFrom`, we can convert `&PyAny` to `&T`.
 ///
 /// This trait is similar to `std::convert::TryFrom`
+#[deprecated(since = "0.21.0")]
 pub trait PyTryFrom<'v>: Sized + PyNativeType {
     /// Cast from a concrete Python object type to PyObject.
+    #[deprecated(
+        since = "0.21.0",
+        note = "use `value.downcast::<T>()` instead of `T::try_from(value)`"
+    )]
     fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>>;
 
     /// Cast from a concrete Python object type to PyObject. With exact type check.
+    #[deprecated(
+        since = "0.21.0",
+        note = "use `value.downcast_exact::<T>()` instead of `T::try_from_exact(value)`"
+    )]
     fn try_from_exact<V: Into<&'v PyAny>>(value: V) -> Result<&'v Self, PyDowncastError<'v>>;
 
     /// Cast a PyAny to a specific type of PyObject. The caller must
@@ -368,19 +377,33 @@ pub trait PyTryFrom<'v>: Sized + PyNativeType {
     /// # Safety
     ///
     /// Callers must ensure that the type is valid or risk type confusion.
+    #[deprecated(
+        since = "0.21.0",
+        note = "use `value.downcast_unchecked::<T>()` instead of `T::try_from_unchecked(value)`"
+    )]
     unsafe fn try_from_unchecked<V: Into<&'v PyAny>>(value: V) -> &'v Self;
 }
 
 /// Trait implemented by Python object types that allow a checked downcast.
 /// This trait is similar to `std::convert::TryInto`
+#[deprecated(since = "0.21.0")]
 pub trait PyTryInto<T>: Sized {
     /// Cast from PyObject to a concrete Python object type.
+    #[deprecated(
+        since = "0.21.0",
+        note = "use `value.downcast()` instead of `value.try_into()`"
+    )]
     fn try_into(&self) -> Result<&T, PyDowncastError<'_>>;
 
     /// Cast from PyObject to a concrete Python object type. With exact type check.
+    #[deprecated(
+        since = "0.21.0",
+        note = "use `value.downcast()` instead of `value.try_into_exact()`"
+    )]
     fn try_into_exact(&self) -> Result<&T, PyDowncastError<'_>>;
 }
 
+#[allow(deprecated)]
 mod implementations {
     use super::*;
 
@@ -555,47 +578,50 @@ mod test_no_clone {}
 
 #[cfg(test)]
 mod tests {
-    use crate::PyObject;
+    use crate::{PyObject, Python};
 
-    use super::super::PyTryFrom;
-    use crate::types::{IntoPyDict, PyAny, PyDict, PyList};
-    use crate::{Python, ToPyObject};
+    #[allow(deprecated)]
+    mod deprecated {
+        use super::super::PyTryFrom;
+        use crate::types::{IntoPyDict, PyAny, PyDict, PyList};
+        use crate::{Python, ToPyObject};
 
-    #[test]
-    fn test_try_from() {
-        Python::with_gil(|py| {
-            let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
-            let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();
+        #[test]
+        fn test_try_from() {
+            Python::with_gil(|py| {
+                let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
+                let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();
 
-            assert!(<PyList as PyTryFrom<'_>>::try_from(list).is_ok());
-            assert!(<PyDict as PyTryFrom<'_>>::try_from(dict).is_ok());
+                assert!(<PyList as PyTryFrom<'_>>::try_from(list).is_ok());
+                assert!(<PyDict as PyTryFrom<'_>>::try_from(dict).is_ok());
 
-            assert!(<PyAny as PyTryFrom<'_>>::try_from(list).is_ok());
-            assert!(<PyAny as PyTryFrom<'_>>::try_from(dict).is_ok());
-        });
-    }
+                assert!(<PyAny as PyTryFrom<'_>>::try_from(list).is_ok());
+                assert!(<PyAny as PyTryFrom<'_>>::try_from(dict).is_ok());
+            });
+        }
 
-    #[test]
-    fn test_try_from_exact() {
-        Python::with_gil(|py| {
-            let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
-            let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();
+        #[test]
+        fn test_try_from_exact() {
+            Python::with_gil(|py| {
+                let list: &PyAny = vec![3, 6, 5, 4, 7].to_object(py).into_ref(py);
+                let dict: &PyAny = vec![("reverse", true)].into_py_dict(py).as_ref();
 
-            assert!(PyList::try_from_exact(list).is_ok());
-            assert!(PyDict::try_from_exact(dict).is_ok());
+                assert!(PyList::try_from_exact(list).is_ok());
+                assert!(PyDict::try_from_exact(dict).is_ok());
 
-            assert!(PyAny::try_from_exact(list).is_err());
-            assert!(PyAny::try_from_exact(dict).is_err());
-        });
-    }
+                assert!(PyAny::try_from_exact(list).is_err());
+                assert!(PyAny::try_from_exact(dict).is_err());
+            });
+        }
 
-    #[test]
-    fn test_try_from_unchecked() {
-        Python::with_gil(|py| {
-            let list = PyList::new(py, [1, 2, 3]);
-            let val = unsafe { <PyList as PyTryFrom>::try_from_unchecked(list.as_ref()) };
-            assert!(list.is(val));
-        });
+        #[test]
+        fn test_try_from_unchecked() {
+            Python::with_gil(|py| {
+                let list = PyList::new(py, [1, 2, 3]);
+                let val = unsafe { <PyList as PyTryFrom>::try_from_unchecked(list.as_ref()) };
+                assert!(list.is(val));
+            });
+        }
     }
 
     #[test]

src/instance.rs

@@ -1614,7 +1614,7 @@ a = A()
 
     #[cfg(feature = "macros")]
     mod using_macros {
-        use crate::{PyCell, PyTryInto};
+        use crate::PyCell;
 
         use super::*;
 
@@ -1642,7 +1642,9 @@ a = A()
         }
 
         #[test]
+        #[allow(deprecated)]
         fn cell_tryfrom() {
+            use crate::PyTryInto;
             // More detailed tests of the underlying semantics in pycell.rs
             Python::with_gil(|py| {
                 let instance: &PyAny = Py::new(py, SomeClass(0)).unwrap().into_ref(py);

src/lib.rs

@@ -295,6 +295,7 @@
 //! [`Ungil`]: crate::marker::Ungil
 pub use crate::class::*;
 pub use crate::conversion::{AsPyPointer, FromPyObject, FromPyPointer, IntoPy, ToPyObject};
+#[allow(deprecated)]
 pub use crate::conversion::{PyTryFrom, PyTryInto};
 pub use crate::err::{PyDowncastError, PyErr, PyErrArguments, PyResult};
 pub use crate::gil::GILPool;

src/prelude.rs

@@ -9,6 +9,7 @@
 //! ```
 
 pub use crate::conversion::{FromPyObject, IntoPy, ToPyObject};
+#[allow(deprecated)]
 pub use crate::conversion::{PyTryFrom, PyTryInto};
 pub use crate::err::{PyErr, PyResult};
 pub use crate::instance::{Py, PyObject};

src/type_object.rs

@@ -23,7 +23,6 @@ pub trait PySizedLayout<T>: PyLayout<T> + Sized {}
 ///
 /// This is expected to be deprecated in the near future, see <https://github.com/PyO3/pyo3/issues/3382>
 ///
-///
 /// # Safety
 ///
 /// - `Py<Self>::as_ref` will hand out references to `Self::AsRefTarget`.

src/types/iterator.rs

@@ -79,6 +79,7 @@ impl PyTypeCheck for PyIterator {
     }
 }
 
+#[allow(deprecated)]
 impl<'v> crate::PyTryFrom<'v> for PyIterator {
     fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v PyIterator, PyDowncastError<'v>> {
         let value = value.into();

src/types/mapping.rs

@@ -135,6 +135,7 @@ impl PyTypeCheck for PyMapping {
     }
 }
 
+#[allow(deprecated)]
 impl<'v> crate::PyTryFrom<'v> for PyMapping {
     /// Downcasting to `PyMapping` requires the concrete class to be a subclass (or registered
     /// subclass) of `collections.abc.Mapping` (from the Python standard library) - i.e.
@@ -168,7 +169,7 @@ mod tests {
     use crate::{
         exceptions::PyKeyError,
         types::{PyDict, PyTuple},
-        PyTryFrom, Python,
+        Python,
     };
 
     use super::*;
@@ -318,7 +319,9 @@ mod tests {
     }
 
     #[test]
+    #[allow(deprecated)]
     fn test_mapping_try_from() {
+        use crate::PyTryFrom;
         Python::with_gil(|py| {
             let dict = PyDict::new(py);
             let _ = <PyMapping as PyTryFrom>::try_from(dict).unwrap();

src/types/sequence.rs

@@ -549,6 +549,7 @@ impl PyTypeCheck for PySequence {
     }
 }
 
+#[allow(deprecated)]
 impl<'v> crate::PyTryFrom<'v> for PySequence {
     /// Downcasting to `PySequence` requires the concrete class to be a subclass (or registered
     /// subclass) of `collections.abc.Sequence` (from the Python standard library) - i.e.
@@ -577,7 +578,7 @@ impl<'v> crate::PyTryFrom<'v> for PySequence {
 #[cfg(test)]
 mod tests {
     use crate::types::{PyList, PySequence, PyTuple};
-    use crate::{PyObject, PyTryFrom, Python, ToPyObject};
+    use crate::{PyObject, Python, ToPyObject};
 
     fn get_object() -> PyObject {
         // Convenience function for getting a single unique object
@@ -1078,7 +1079,9 @@ mod tests {
     }
 
     #[test]
+    #[allow(deprecated)]
     fn test_seq_try_from() {
+        use crate::PyTryFrom;
         Python::with_gil(|py| {
             let list = PyList::empty(py);
             let _ = <PySequence as PyTryFrom>::try_from(list).unwrap();