Fix streamed list of union basemodels

instructor/dsl/partial.py

@@ -19,6 +19,7 @@
     NoReturn,
     Optional,
     TypeVar,
+    Union,
 )
 from collections.abc import AsyncGenerator, Generator, Iterable
 from copy import deepcopy
@@ -38,41 +39,57 @@ def _make_field_optional(
     field: FieldInfo,
 ) -> tuple[Any, FieldInfo]:
     tmp_field = deepcopy(field)
-
     annotation = field.annotation
 
     # Handle generics (like List, Dict, etc.)
     if get_origin(annotation) is not None:
-        # Get the generic base (like List, Dict) and its arguments (like User in List[User])
         generic_base = get_origin(annotation)
         generic_args = get_args(annotation)
 
-        # Recursively apply Partial to each of the generic arguments
-        modified_args = tuple(
-            (
-                Partial[arg, MakeFieldsOptional]  # type: ignore[valid-type]
-                if isinstance(arg, type) and issubclass(arg, BaseModel)
+        # Handle Union types specially
+        if generic_base is Union:
+            modified_args = tuple(
+                Partial[arg, MakeFieldsOptional] if isinstance(arg, type) and issubclass(arg, BaseModel)
                 else arg
+                for arg in generic_args
             )
-            for arg in generic_args
-        )
-
-        # Reconstruct the generic type with modified arguments
-        tmp_field.annotation = (
-            Optional[generic_base[modified_args]] if generic_base else None
-        )
-        tmp_field.default = None
-    # If the field is a BaseModel, then recursively convert it's
-    # attributes to optionals.
+            # Add None to Union options and set default
+            modified_args = modified_args + (None,) if None not in modified_args else modified_args
+            tmp_field.annotation = Union[modified_args]  # type: ignore
+            tmp_field.default = None
+        else:
+            # For other generics (like List), process their arguments
+            modified_args = tuple(
+                _process_annotation(arg)
+                for arg in generic_args
+            )
+            tmp_field.annotation = Optional[generic_base[modified_args]]  # type: ignore
+            tmp_field.default = None
+    # If the field is a BaseModel, then recursively convert it's attributes to optionals
     elif isinstance(annotation, type) and issubclass(annotation, BaseModel):
-        tmp_field.annotation = Optional[Partial[annotation, MakeFieldsOptional]]  # type: ignore[assignment, valid-type]
-        tmp_field.default = {}
+        tmp_field.annotation = Optional[Partial[annotation, MakeFieldsOptional]]  # type: ignore
+        tmp_field.default = None
     else:
-        tmp_field.annotation = Optional[field.annotation]  # type: ignore[assignment]
+        tmp_field.annotation = Optional[annotation]  # type: ignore
         tmp_field.default = None
 
     return tmp_field.annotation, tmp_field  # type: ignore
 
+def _process_annotation(annotation: Any) -> Any:
+    """Helper function to process nested annotations"""
+    if get_origin(annotation) is Union:
+        modified_args = tuple(
+            Partial[arg, MakeFieldsOptional] if isinstance(arg, type) and issubclass(arg, BaseModel)
+            else arg
+            for arg in get_args(annotation)
+        )
+        # Add None to Union options
+        modified_args = modified_args + (None,) if None not in modified_args else modified_args
+        return Union[modified_args]
+    elif isinstance(annotation, type) and issubclass(annotation, BaseModel):
+        return Partial[annotation, MakeFieldsOptional]
+    return annotation
+
 
 class PartialBase(Generic[T_Model]):
     @classmethod