Preserve str subclass returned by __repr__

Copilot · youknowone · Copilot · commit 0852fa63b3c5 · 2026-03-17T11:27:11.000Z
Co-authored-by: youknowone &lt;69878+youknowone@users.noreply.github.com&gt;
diff --git a/Lib/test/test_str.py b/Lib/test/test_str.py
@@ -2415,7 +2415,6 @@ def test_ucs4(self):
         else:
             self.fail("Should have raised UnicodeDecodeError")
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; AssertionError: <class 'str'> is not <class 'test.test_str.StrSubclass'>
     def test_conversion(self):
         # Make sure __str__() works properly
         class StrWithStr(str):
diff --git a/crates/vm/src/builtins/str.rs b/crates/vm/src/builtins/str.rs
@@ -394,13 +394,12 @@ impl Constructor for PyStr {
     type Args = StrArgs;
 
     fn slot_new(cls: PyTypeRef, func_args: FuncArgs, vm: &VirtualMachine) -> PyResult {
-        // Optimization: return exact str as-is (only when no encoding/errors provided)
+        // Optimization: for exact str, return PyObject_Str result as-is
         if cls.is(vm.ctx.types.str_type)
             && func_args.args.len() == 1
             && func_args.kwargs.is_empty()
-            && func_args.args[0].class().is(vm.ctx.types.str_type)
         {
-            return Ok(func_args.args[0].clone());
+            return func_args.args[0].str(vm).map(Into::into);
         }
 
         let args: Self::Args = func_args.bind(vm)?;

Original file line number	Diff line number	Diff line change
`@@ -394,13 +394,12 @@ impl Constructor for PyStr {`
`394`	`394`	`type Args = StrArgs;`
`395`	`395`
`396`	`396`	`fn slot_new(cls: PyTypeRef, func_args: FuncArgs, vm: &VirtualMachine) -> PyResult {`
`397`		`- // Optimization: return exact str as-is (only when no encoding/errors provided)`
	`397`	`+ // Optimization: for exact str, return PyObject_Str result as-is`
`398`	`398`	`if cls.is(vm.ctx.types.str_type)`
`399`	`399`	`&& func_args.args.len() == 1`
`400`	`400`	`&& func_args.kwargs.is_empty()`
`401`		`- && func_args.args[0].class().is(vm.ctx.types.str_type)`
`402`	`401`	`{`
`403`		`- return Ok(func_args.args[0].clone());`
	`402`	`+ return func_args.args[0].str(vm).map(Into::into);`
`404`	`403`	`}`
`405`	`404`
`406`	`405`	`let args: Self::Args = func_args.bind(vm)?;`