Match CPython's "argument of type ... is not a container or iterable" wording (RustPython#7714)

changjoon-park · web-flow · commit 04ffa3891c3b · 2026-04-29T18:29:31.000+09:00
CPython's PySequence_Contains (Objects/abstract.c::_PySequence_IterSearch)
catches the TypeError from PyObject_GetIter when neither __contains__ nor
__iter__ is available, and re-raises with membership-test wording.

RustPython's PySequence::contains propagated the get_iter error verbatim,
so '1 in obj' produced 'X' object is not iterable — a literal but less
specific message.

Wrap the get_iter call in map_err: when the failure is a TypeError,
re-raise with byte-identical CPython wording. Other exception types pass
through unchanged.

Unmasks test_contains.TestContains.test_common_tests.
diff --git a/Lib/test/test_contains.py b/Lib/test/test_contains.py
@@ -16,7 +16,6 @@ def __getitem__(self, n):
         return [self.el][n]
 
 class TestContains(unittest.TestCase):
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; Wrong error message
     def test_common_tests(self):
         a = base_set(1)
         b = myset(1)
diff --git a/crates/vm/src/protocol/sequence.rs b/crates/vm/src/protocol/sequence.rs
@@ -1,5 +1,5 @@
 use crate::{
-    PyObject, PyObjectRef, PyPayload, PyResult, VirtualMachine,
+    AsObject, PyObject, PyObjectRef, PyPayload, PyResult, VirtualMachine,
     builtins::{PyList, PyListRef, PySlice, PyTuple, PyTupleRef},
     convert::ToPyObject,
     function::PyArithmeticValue,
@@ -398,7 +398,19 @@ impl PySequence<'_> {
             return f(self, target, vm);
         }
 
-        let iter = self.obj.to_owned().get_iter(vm)?;
+        // CPython parity: when neither __contains__ nor __iter__ is available,
+        // `PySequence_Contains` rewords the get_iter TypeError into the
+        // membership-test wording. Other exception types propagate unchanged.
+        let iter = self.obj.to_owned().get_iter(vm).map_err(|e| {
+            if e.fast_isinstance(vm.ctx.exceptions.type_error) {
+                vm.new_type_error(format!(
+                    "argument of type '{}' is not a container or iterable",
+                    self.obj.class().name()
+                ))
+            } else {
+                e
+            }
+        })?;
         let iter = iter.iter::<PyObjectRef>(vm)?;
 
         for elem in iter {
