Provide a special purpose FromPyObject impl to efficiently and safely…

… get a byte slice from either bytes or byte arrays.

pyo3-macros-backend/src/frompyobject.rs

@@ -278,7 +278,6 @@ impl<'a> Container<'a> {
         let self_ty = &self.path;
         let struct_name = &self.name();
         let field_idents: Vec<_> = (0..struct_fields.len())
-            .into_iter()
             .map(|i| format_ident!("arg{}", i))
             .collect();
         let fields = struct_fields.iter().zip(&field_idents).enumerate().map(|(index, (field, ident))| {

pyo3-macros-backend/src/pymethod.rs

@@ -1109,7 +1109,6 @@ impl SlotDef {
         let py = syn::Ident::new("_py", Span::call_site());
         let arg_types: &Vec<_> = &arguments.iter().map(|arg| arg.ffi_type()).collect();
         let arg_idents: &Vec<_> = &(0..arguments.len())
-            .into_iter()
             .map(|i| format_ident!("arg{}", i))
             .collect();
         let wrapper_ident = format_ident!("__pymethod_{}__", method_name);
@@ -1220,7 +1219,6 @@ impl SlotFragmentDef {
         let py = syn::Ident::new("_py", Span::call_site());
         let arg_types: &Vec<_> = &arguments.iter().map(|arg| arg.ffi_type()).collect();
         let arg_idents: &Vec<_> = &(0..arguments.len())
-            .into_iter()
             .map(|i| format_ident!("arg{}", i))
             .collect();
         let body = generate_method_body(cls, spec, &py, arguments, *extract_error_mode, None)?;

src/types/bytes.rs

@@ -1,9 +1,12 @@
-use crate::{ffi, AsPyPointer, Py, PyAny, PyResult, Python};
+use crate::{ffi, AsPyPointer, FromPyObject, Py, PyAny, PyResult, Python};
+use std::borrow::Cow;
 use std::ops::Index;
 use std::os::raw::c_char;
 use std::slice::SliceIndex;
 use std::str;
 
+use super::bytearray::PyByteArray;
+
 /// Represents a Python `bytes` object.
 ///
 /// This type is immutable.
@@ -121,6 +124,18 @@ impl<I: SliceIndex<[u8]>> Index<I> for PyBytes {
     }
 }
 
+/// Special-purpose trait impl to efficient handle [`PyBytes`] and [`PyByteArray`]
+impl<'source> FromPyObject<'source> for Cow<'source, [u8]> {
+    fn extract(ob: &'source PyAny) -> PyResult<Self> {
+        if let Ok(bytes) = ob.downcast::<PyBytes>() {
+            return Ok(Cow::Borrowed(bytes.as_bytes()));
+        }
+
+        let byte_array = ob.downcast::<PyByteArray>()?;
+        Ok(Cow::Owned(byte_array.to_vec()))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::PyBytes;