Merge pull request #2181 from RicoHageman/from_py_with_tuple_struct

Add support for `from_py_with` on struct tuples and enums

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `PyAny::contains` method (`in` operator for `PyAny`). [#2115](https://github.com/PyO3/pyo3/pull/2115)
 - Add `PyMapping::contains` method (`in` operator for `PyMapping`). [#2133](https://github.com/PyO3/pyo3/pull/2133)
 - Add garbage collection magic methods `__traverse__` and `__clear__` to `#[pymethods]`. [#2159](https://github.com/PyO3/pyo3/pull/2159)
+- Add support for `from_py_with` on struct tuples and enums to override the default from-Python conversion. [#2181](https://github.com/PyO3/pyo3/pull/2181)
 
 ### Changed
 

guide/src/conversions/traits.md

@@ -442,6 +442,10 @@ If the input is neither a string nor an integer, the error message will be:
 - `pyo3(item)`, `pyo3(item("key"))`
     - retrieve the field from a mapping, possibly with the custom key specified as an argument.
     - can be any literal that implements `ToBorrowedObject`
+- `pyo3(from_py_with = "...")`
+    - apply a custom function to convert the field from Python the desired Rust type. 
+    - the argument must be the name of the function as a string.
+    - the function signature must be `fn(&PyAny) -> PyResult<T>` where `T` is the Rust type of the argument.
 
 ### `IntoPy<T>`
 

pyo3-macros-backend/src/frompyobject.rs

@@ -106,8 +106,9 @@ enum ContainerType<'a> {
     StructNewtype(&'a Ident),
     /// Tuple struct, e.g. `struct Foo(String)`.
     ///
-    /// Fields are extracted from a tuple.
-    Tuple(usize),
+    /// Variant contains a list of conversion methods for each of the fields that are directly
+    ///  extracted from the tuple.
+    Tuple(Vec<FieldPyO3Attributes>),
     /// Tuple newtype, e.g. `#[transparent] struct Foo(String)`
     ///
     /// The wrapped field is directly extracted from the object.
@@ -149,7 +150,15 @@ impl<'a> Container<'a> {
             (Fields::Unnamed(_), true) => ContainerType::TupleNewtype,
             (Fields::Unnamed(unnamed), false) => match unnamed.unnamed.len() {
                 1 => ContainerType::TupleNewtype,
-                len => ContainerType::Tuple(len),
+                _ => {
+                    let fields = unnamed
+                        .unnamed
+                        .iter()
+                        .map(|field| FieldPyO3Attributes::from_attrs(&field.attrs))
+                        .collect::<Result<Vec<_>>>()?;
+
+                    ContainerType::Tuple(fields)
+                }
             },
             (Fields::Named(named), true) => {
                 let field = named
@@ -196,7 +205,7 @@ impl<'a> Container<'a> {
         match &self.ty {
             ContainerType::StructNewtype(ident) => self.build_newtype_struct(Some(ident)),
             ContainerType::TupleNewtype => self.build_newtype_struct(None),
-            ContainerType::Tuple(len) => self.build_tuple_struct(*len),
+            ContainerType::Tuple(tups) => self.build_tuple_struct(tups),
             ContainerType::Struct(tups) => self.build_struct(tups),
         }
     }
@@ -233,19 +242,33 @@ impl<'a> Container<'a> {
         }
     }
 
-    fn build_tuple_struct(&self, len: usize) -> TokenStream {
+    fn build_tuple_struct(&self, tups: &[FieldPyO3Attributes]) -> TokenStream {
         let self_ty = &self.path;
         let mut fields: Punctuated<TokenStream, syn::Token![,]> = Punctuated::new();
-        for i in 0..len {
-            let error_msg = format!("failed to extract field {}.{}", quote!(#self_ty), i);
-            fields.push(quote!(
-                s.get_item(#i).and_then(_pyo3::types::PyAny::extract).map_err(|inner| {
-                let py = _pyo3::PyNativeType::py(obj);
-                let new_err = _pyo3::exceptions::PyTypeError::new_err(#error_msg);
-                new_err.set_cause(py, ::std::option::Option::Some(inner));
-                new_err
-                })?));
+        for (index, attrs) in tups.iter().enumerate() {
+            let error_msg = format!("failed to extract field {}.{}", quote!(#self_ty), index);
+
+            let parsed_item = match &attrs.from_py_with {
+                None => quote!(
+                    obj.get_item(#index)?.extract()
+                ),
+                Some(FromPyWithAttribute(expr_path)) => quote! (
+                    #expr_path(obj.get_item(#index)?)
+                ),
+            };
+
+            let extractor = quote!(
+                #parsed_item.map_err(|inner| {
+                    let py = _pyo3::PyNativeType::py(obj);
+                    let new_err = _pyo3::exceptions::PyTypeError::new_err(#error_msg);
+                    new_err.set_cause(py, ::std::option::Option::Some(inner));
+                    new_err
+                })?
+            );
+
+            fields.push(quote!(#extractor));
         }
+        let len = tups.len();
         let msg = if self.is_enum_variant {
             quote!(::std::format!(
                 "expected tuple of length {}, but got length {}",

pyo3-macros-backend/src/pyclass.rs

@@ -71,7 +71,7 @@ impl PyClassArgs {
         }
     }
 
-    /// Adda single expression from the comma separated list in the attribute, which is
+    /// Add a single expression from the comma separated list in the attribute, which is
     /// either a single word or an assignment expression
     fn add_expr(&mut self, expr: &Expr) -> Result<()> {
         match expr {

tests/test_frompyobject.rs

@@ -481,3 +481,40 @@ fn test_from_py_with() {
         assert_eq!(zap.some_object_length, 3usize);
     });
 }
+
+#[derive(Debug, FromPyObject)]
+pub struct ZapTuple(String, #[pyo3(from_py_with = "PyAny::len")] usize);
+
+#[test]
+fn test_from_py_with_tuple_struct() {
+    Python::with_gil(|py| {
+        let py_zap = py
+            .eval(r#"("whatever", [1, 2, 3])"#, None, None)
+            .expect("failed to create tuple");
+
+        let zap = ZapTuple::extract(py_zap).unwrap();
+
+        assert_eq!(zap.0, "whatever");
+        assert_eq!(zap.1, 3usize);
+    });
+}
+
+#[derive(Debug, FromPyObject, PartialEq)]
+pub enum ZapEnum {
+    Zip(#[pyo3(from_py_with = "PyAny::len")] usize),
+    Zap(String, #[pyo3(from_py_with = "PyAny::len")] usize),
+}
+
+#[test]
+fn test_from_py_with_enum() {
+    Python::with_gil(|py| {
+        let py_zap = py
+            .eval(r#"("whatever", [1, 2, 3])"#, None, None)
+            .expect("failed to create tuple");
+
+        let zap = ZapEnum::extract(py_zap).unwrap();
+        let expected_zap = ZapEnum::Zap(String::from("whatever"), 3usize);
+
+        assert_eq!(zap, expected_zap);
+    });
+}