Try __await__ method for generator subclasses in anext_awaitable

moreal · claude · moreal · commit b76dde11c547 · 2026-01-22T17:52:26.000+09:00
For generators without CO_ITERABLE_COROUTINE flag, try to get __await__
method instead of returning an error immediately. This matches CPython's
_PyCoro_GetAwaitableIter behavior which allows generator subclasses that
define __await__ to be used in await expressions.

Co-Authored-By: Claude Opus 4.5 &lt;noreply@anthropic.com&gt;
diff --git a/crates/vm/src/builtins/asyncgenerator.rs b/crates/vm/src/builtins/asyncgenerator.rs
@@ -604,6 +604,10 @@ impl PyAnextAwaitable {
             {
                 // Return the generator itself as the iterator
                 return Ok(wrapped.clone());
+            }
+            // Fall through: try to get __await__ method for generator subclasses
+            if let Some(await_method) = vm.get_method(wrapped.clone(), identifier!(vm, __await__)) {
+                await_method?.call((), vm)?
             } else {
                 return Err(vm.new_type_error(format!(
                     "object {} can't be used in 'await' expression",
