itemsize

RustPython · youknowone · Dec 28, 2025 · Dec 26, 2025 · Dec 26, 2025 · Dec 27, 2025
commit 028c05fc17304d4756f564e4233c2df9f096501f
diff --git a/crates/derive-impl/src/pyclass.rs b/crates/derive-impl/src/pyclass.rs
@@ -165,6 +165,7 @@ pub(crate) fn impl_pyclass_impl(attr: PunctuatedNestedMeta, item: Item) -> Resul
                 with_impl,
                 with_method_defs,
                 with_slots,
+                itemsize,
             } = extract_impl_attrs(attr, &impl_ty)?;
             let payload_ty = attr_payload.unwrap_or(payload_guess);
             let method_def = &context.method_items;
@@ -189,9 +190,17 @@ pub(crate) fn impl_pyclass_impl(attr: PunctuatedNestedMeta, item: Item) -> Resul
                         #(#class_extensions)*
                     }
                 },
-                parse_quote! {
-                    fn __extend_slots(slots: &mut ::rustpython_vm::types::PyTypeSlots) {
-                        #slots_impl
+                {
+                    let itemsize_impl = itemsize.as_ref().map(|size| {
+                        quote! {
+                            slots.itemsize = #size;
+                        }
+                    });
+                    parse_quote! {
+                        fn __extend_slots(slots: &mut ::rustpython_vm::types::PyTypeSlots) {
+                            #itemsize_impl
+                            #slots_impl
+                        }
                     }
                 },
             ];
@@ -1618,6 +1627,7 @@ struct ExtractedImplAttrs {
     with_impl: TokenStream,
     with_method_defs: Vec<TokenStream>,
     with_slots: TokenStream,
+    itemsize: Option<syn::Expr>,
 }
 
 fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<ExtractedImplAttrs> {
@@ -1636,6 +1646,7 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
         }
     }];
     let mut payload = None;
+    let mut itemsize = None;
 
     for attr in attr {
         match attr {
@@ -1721,6 +1732,8 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
                     } else {
                         bail_span!(value, "payload must be a string literal")
                     }
+                } else if path.is_ident("itemsize") {
+                    itemsize = Some(value);
                 } else {
                     bail_span!(path, "Unknown pyimpl attribute")
                 }
@@ -1741,6 +1754,7 @@ fn extract_impl_attrs(attr: PunctuatedNestedMeta, item: &Ident) -> Result<Extrac
         with_slots: quote! {
             #(#with_slots)*
         },
+        itemsize,
     })
 }
 

diff --git a/crates/vm/src/builtins/bytes.rs b/crates/vm/src/builtins/bytes.rs
@@ -187,6 +187,7 @@ impl PyRef<PyBytes> {
 }
 
 #[pyclass(
+    itemsize = 1,
     flags(BASETYPE, _MATCH_SELF),
     with(
         Py,

diff --git a/crates/vm/src/builtins/int.rs b/crates/vm/src/builtins/int.rs
@@ -320,6 +320,7 @@ impl PyInt {
 }
 
 #[pyclass(
+    itemsize = 4,
     flags(BASETYPE, _MATCH_SELF),
     with(PyRef, Comparable, Hashable, Constructor, AsNumber, Representable)
 )]

diff --git a/crates/vm/src/builtins/tuple.rs b/crates/vm/src/builtins/tuple.rs
@@ -257,16 +257,9 @@ impl<T> PyTuple<PyRef<T>> {
 }
 
 #[pyclass(
+    itemsize = std::mem::size_of::<crate::PyObjectRef>(),
     flags(BASETYPE, SEQUENCE, _MATCH_SELF),
-    with(
-        AsMapping,
-        AsSequence,
-        Hashable,
-        Comparable,
-        Iterable,
-        Constructor,
-        Representable
-    )
+    with(AsMapping, AsSequence, Hashable, Comparable, Iterable, Constructor, Representable)
 )]
 impl PyTuple {
     #[pymethod]

diff --git a/crates/vm/src/builtins/type.rs b/crates/vm/src/builtins/type.rs
@@ -948,6 +948,11 @@ impl PyType {
         self.slots.basicsize
     }
 
+    #[pygetset]
+    fn __itemsize__(&self) -> usize {
+        self.slots.itemsize
+    }
+
     #[pygetset]
     pub fn __name__(&self, vm: &VirtualMachine) -> PyStrRef {
         self.name_inner(
@@ -2088,12 +2093,16 @@ fn solid_base<'a>(typ: &'a Py<PyType>, vm: &VirtualMachine) -> &'a Py<PyType> {
         vm.ctx.types.object_type
     };
 
-    // TODO: requires itemsize comparison too
-    if typ.__basicsize__() != base.__basicsize__() {
-        typ
-    } else {
-        base
-    }
+    // Check for extra instance variables (CPython's extra_ivars)
+    let t_size = typ.__basicsize__();
+    let b_size = base.__basicsize__();
+    let t_itemsize = typ.slots.itemsize;
+    let b_itemsize = base.slots.itemsize;
+
+    // Has extra ivars if: sizes differ AND (has items OR t_size > b_size)
+    let has_extra_ivars = t_size != b_size && (t_itemsize > 0 || b_itemsize > 0 || t_size > b_size);
+
+    if has_extra_ivars { typ } else { base }
 }
 
 fn best_base<'a>(bases: &'a [PyTypeRef], vm: &VirtualMachine) -> PyResult<&'a Py<PyType>> {

diff --git a/crates/vm/src/class.rs b/crates/vm/src/class.rs
@@ -70,6 +70,7 @@ pub trait PyClassDef {
     const TP_NAME: &'static str;
     const DOC: Option<&'static str> = None;
     const BASICSIZE: usize;
+    const ITEMSIZE: usize = 0;
     const UNHASHABLE: bool = false;
 
     // due to restriction of rust trait system, object.__base__ is None
@@ -210,6 +211,7 @@ pub trait PyClassImpl: PyClassDef {
             flags: Self::TP_FLAGS,
             name: Self::TP_NAME,
             basicsize: Self::BASICSIZE,
+            itemsize: Self::ITEMSIZE,
             doc: Self::DOC,
             methods: Self::METHOD_DEFS,
             ..Default::default()

diff --git a/crates/vm/src/types/slot.rs b/crates/vm/src/types/slot.rs
@@ -128,7 +128,7 @@ pub struct PyTypeSlots {
     pub(crate) name: &'static str, // tp_name with <module>.<class> for print, not class name
 
     pub basicsize: usize,
-    // tp_itemsize
+    pub itemsize: usize, // tp_itemsize
 
     // Methods to implement standard operations
-Original file line number
+Diff line change
@@ Expand Up / @@ -187,6 +187,7 @@ impl PyRef<PyBytes> { @@
     }
     #[pyclass(
+        itemsize = 1,
         flags(BASETYPE, _MATCH_SELF),
         with(
             Py,
@@ Expand Down @@