youknowone · Oct 9, 2026 · Oct 4, 2026 · Oct 4, 2026 · Oct 6, 2026 · Oct 8, 2026
diff --git a/Lib/test/test_extcall.py b/Lib/test/test_extcall.py
@@ -442,7 +442,7 @@
     ...     False
     True
 
-    >>> id(1, **{'foo': 1}) # TODO: RUSTPYTHON # doctest:+EXPECTED_FAILURE
+    >>> id(1, **{'foo': 1})
     Traceback (most recent call last):
       ...
     TypeError: id() takes no keyword arguments

diff --git a/crates/capi/src/methodobject.rs b/crates/capi/src/methodobject.rs
@@ -385,4 +385,26 @@ mod tests {
             func.call0().unwrap();
         });
     }
+
+    #[test]
+    fn no_keywords_before_arity() {
+        Python::attach(|py| {
+            unsafe extern "C" fn c_fn(_self: *mut PyObject, _args: *mut PyObject) -> *mut PyObject {
+                unsafe { PyLong_FromLong(42) }
+            }
+            let f = PyCFunction::new(py, c_fn, c"no_keywords", c"", None).unwrap();
+            let kwargs = pyo3::types::PyDict::new(py);
+            kwargs.set_item("unexpected", 1).unwrap();
+            let err = f.call((1,), Some(&kwargs)).unwrap_err();
+            assert_eq!(
+                err.value(py).str().unwrap().to_str().unwrap(),
+                "no_keywords() takes no keyword arguments"
+            );
+            kwargs.clear();
+            assert_eq!(
+                f.call((), Some(&kwargs)).unwrap().extract::<i32>().unwrap(),
+                42
+            );
+        });
+    }
 }
diff --git a/crates/vm/src/builtins/builtin_func.rs b/crates/vm/src/builtins/builtin_func.rs
@@ -87,6 +87,9 @@ impl Callable for PyNativeFunction {
     type Args = FuncArgs;
     #[inline]
     fn call(zelf: &Py<Self>, mut args: FuncArgs, vm: &VirtualMachine) -> PyResult {
+        if !args.kwargs.is_empty() && !zelf.value.flags.contains(PyMethodFlags::KEYWORDS) {
+            return Err(native_no_keywords_error(zelf, vm)?);
+        }
         let mut callee = Callee::named(zelf.value.name);
         if let Some(z) = &zelf.zelf {
             // STATIC methods store the class in zelf for qualname/repr purposes,
@@ -272,6 +275,12 @@ fn vectorcall_native_function(
 ) -> PyResult {
     let zelf: &Py<PyNativeFunction> = zelf_obj.downcast_ref().unwrap();
 
+    if kwnames.is_some_and(|names| !names.is_empty())
+        && !zelf.value.flags.contains(PyMethodFlags::KEYWORDS)
+    {
+        return Err(native_no_keywords_error(zelf, vm)?);
+    }
+
     // Build FuncArgs with self already at position 0 (no insert(0) needed)
     let needs_self = zelf
         .zelf
@@ -292,6 +301,30 @@ fn vectorcall_native_function(
     (zelf.value.func)(vm, func_args, callee)
 }
 
+#[cold]
+fn native_no_keywords_error(
+    zelf: &Py<PyNativeFunction>,
+    vm: &VirtualMachine,
+) -> PyResult<crate::exceptions::types::PyBaseExceptionRef> {
+    if zelf.value.flags.contains(PyMethodFlags::VARARGS) {
+        return Ok(vm.new_type_error(format!("{}() takes no keyword arguments", zelf.value.name)));
+    }
+    let qualname = PyNativeFunction::__qualname__(NativeFunctionOrMethod(zelf.to_owned()), vm)?;
+    let module = zelf
+        .module
+        .load_owned()
+        .filter(|module| !vm.is_none(module));
+    let module = module.map(|module| module.str(vm)).transpose()?;
+    let name = if let Some(module) = module
+        && module.to_string() != "builtins"
+    {
+        format!("{module}.{qualname}")
+    } else {
+        qualname.to_string()
+    };
+    Ok(vm.new_type_error(format!("{name}() takes no keyword arguments")))
+}
+
 pub(crate) fn init(context: &'static Context) {
     PyNativeFunction::extend_class(context, context.types.builtin_function_or_method_type);
     context

diff --git a/crates/vm/src/builtins/descriptor.rs b/crates/vm/src/builtins/descriptor.rs
@@ -112,8 +112,9 @@ impl Callable for PyMethodDescriptor {
     type Args = FuncArgs;
     #[inline]
     fn call(zelf: &Py<Self>, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
-        if let Some(obj) = args.args.first() {
-            method_descr_typecheck(zelf, obj, vm)?;
+        method_descr_check_self(zelf, args.args.first().map(|obj| &**obj), vm)?;
+        if !args.kwargs.is_empty() && !zelf.method.flags.contains(PyMethodFlags::KEYWORDS) {
+            return Err(method_descr_no_keywords_error(zelf, vm));
         }
         (zelf.method.func)(
             vm,
@@ -1556,6 +1557,40 @@ fn method_descr_typecheck(
     )))
 }
 
+#[inline]
+fn method_descr_check_self(
+    descr: &PyMethodDescriptor,
+    obj: Option<&PyObject>,
+    vm: &VirtualMachine,
+) -> PyResult<()> {
+    let obj = obj.ok_or_else(|| method_descr_missing_self_error(descr, vm))?;
+    method_descr_typecheck(descr, obj, vm)
+}
+
+#[cold]
+fn method_descr_missing_self_error(
+    descr: &PyMethodDescriptor,
+    vm: &VirtualMachine,
+) -> crate::exceptions::types::PyBaseExceptionRef {
+    vm.new_type_error(format!(
+        "unbound method {}.{}() needs an argument",
+        descr.common.typ.name(),
+        descr.common.name
+    ))
+}
+
+#[cold]
+fn method_descr_no_keywords_error(
+    descr: &PyMethodDescriptor,
+    vm: &VirtualMachine,
+) -> crate::exceptions::types::PyBaseExceptionRef {
+    vm.new_type_error(format!(
+        "{}.{}() takes no keyword arguments",
+        descr.common.typ.name(),
+        descr.common.name
+    ))
+}
+
 /// Vectorcall for method_descriptor: calls native method directly
 fn vectorcall_method_descriptor(
     zelf_obj: &PyObject,
@@ -1565,10 +1600,19 @@ fn vectorcall_method_descriptor(
     vm: &VirtualMachine,
 ) -> PyResult {
     let zelf: &Py<PyMethodDescriptor> = zelf_obj.downcast_ref().unwrap();
-    if nargs > 0
-        && let Some(obj) = args.first()
+    method_descr_check_self(
+        zelf,
+        if nargs > 0 {
+            args.first().map(|obj| &**obj)
+        } else {
+            None
+        },
+        vm,
+    )?;
+    if kwnames.is_some_and(|names| !names.is_empty())
+        && !zelf.method.flags.contains(PyMethodFlags::KEYWORDS)
     {
-        method_descr_typecheck(zelf, obj, vm)?;
+        return Err(method_descr_no_keywords_error(zelf, vm));
     }
     let func_args = FuncArgs::from_vectorcall_owned(args, nargs, kwnames);
     (zelf.method.func)(

diff --git a/extra_tests/snippets/syntax_function_args.py b/extra_tests/snippets/syntax_function_args.py
@@ -1,6 +1,90 @@
 from testutils import assert_raises
 
 
+def error(call, expected):
+    try:
+        call()
+    except TypeError as exc:
+        assert str(exc) == expected, (str(exc), expected)
+    else:
+        raise AssertionError("expected TypeError")
+
+
+error(lambda: id(obj=1), "id() takes no keyword arguments")
+error(lambda: id(**{"obj": 1}), "id() takes no keyword arguments")
+error(lambda: id(1, 2, obj=1), "id() takes no keyword arguments")
+error(lambda: list.append(x=1), "unbound method list.append() needs an argument")
+error(lambda: list.append(**{"x": 1}), "unbound method list.append() needs an argument")
+error(
+    lambda: list.append(1, x=1),
+    "descriptor 'append' for 'list' objects doesn't apply to a 'int' object",
+)
+error(lambda: list.append([], x=1), "list.append() takes no keyword arguments")
+error(lambda: list.append([], **{"x": 1}), "list.append() takes no keyword arguments")
+error(lambda: [].append(x=1), "list.append() takes no keyword arguments")
+error(lambda: [].clear(1, x=1), "list.clear() takes no keyword arguments")
+
+
+class Index:
+    def __index__(self):
+        raise AssertionError("conversion ran before keyword check")
+
+
+error(lambda: bin(Index(), x=1), "bin() takes no keyword arguments")
+assert id(1, **{}) == id(1)
+assert round(1.25, ndigits=1) == 1.2
+assert pow(2, exp=3) == 8
+assert sorted([2, 1], reverse=True) == [2, 1]
+assert sum([1, 2], start=4) == 7
+values = []
+list.append(values, 1)
+values.append(2)
+assert values == [1, 2]
+list.clear(values)
+assert values == []
+
+# Keyword metadata must forward raw arguments without changing body validation.
+for choose in (min, max):
+    assert choose([], default=42) == 42
+    assert choose([1, 2], key=lambda value: -value) == (2 if choose is min else 1)
+    try:
+        choose(bogus=1)
+    except TypeError as exc:
+        assert str(exc) == f"{choose.__name__} expected at least 1 argument, got 0"
+    else:
+        raise AssertionError("missing positional argument was accepted")
+    try:
+        choose(1, 2, default=0)
+    except TypeError as exc:
+        assert str(exc) == (
+            f"Cannot specify a default for {choose.__name__}() "
+            "with multiple positional arguments"
+        )
+    else:
+        raise AssertionError("default with multiple arguments was accepted")
+
+# Named fields in argument structs must override positional-only arguments.
+assert eval("value", globals={"value": 42}) == 42
+namespace = {}
+exec("value = 42", globals=namespace)
+assert namespace["value"] == 42
+assert compile(source="42", filename="<inference>", mode="eval")
+assert __import__(name="sys").__name__ == "sys"
+
+from io import StringIO
+
+output = StringIO()
+print(1, 2, sep=":", end="!", file=output)
+assert output.getvalue() == "1:2!"
+
+# Methods using a keyword-only argument struct must keep accepting keywords.
+values = [1, 2]
+values.sort(reverse=True)
+assert values == [2, 1]
+
+# Definitions built without the macros infer their calling convention too.
+assert int.__new__(int, "11", base=2) == 3
+
 def sum(x, y):
     return x+y