fixes

Author: crusaderky

src/array_api_extra/_lib/_utils/_helpers.py

@@ -330,7 +330,11 @@ def _expand() -> object:  # numpydoc ignore=RT01
     -----
     This function must be global in order to be picklable.
     """
-    return next(_repacking_objects.get())
+    try:
+        return next(_repacking_objects.get())
+    except StopIteration:
+        msg = "Not enough objects to repack"
+        raise ValueError(msg) from None
 
 
 def pickle_without(obj: object, *classes: type[T]) -> tuple[bytes, list[T]]:
@@ -390,9 +394,16 @@ def reduce(x: T) -> tuple[Callable[[], object], tuple[()]]:  # numpydoc ignore=G
 
     f = io.BytesIO()
     p = pickle.Pickler(f)
+
+    # Override the reducer for the given classes and all their
+    # subclasses (recursively).
     p.dispatch_table = copyreg.dispatch_table.copy()
-    for cls in classes:
+    subclasses = list(classes)
+    while subclasses:
+        cls = subclasses.pop()
         p.dispatch_table[cls] = reduce
+        subclasses.extend(cls.__subclasses__())
+
     p.dump(obj)
 
     return f.getvalue(), extracted