fix(sdk): Components - Fixed handling of typing.NamedTuple in Python …

…3.9 (#4614)

Python 3.9 has dropped support for `typing.NamedTuple(...)`.`_field_types` in favor of `__annotations__` which in turn does not exist in Python 3.5.

sdk/python/kfp/components/_python_op.py

@@ -351,10 +351,14 @@ def annotation_to_type_struct(annotation):
     #Analyzing the return type annotations.
     return_ann = signature.return_annotation
     if hasattr(return_ann, '_fields'): #NamedTuple
+        # Getting field type annotations.
+        # __annotations__ does not exist in python 3.5 and earlier
+        # _field_types does not exist in python 3.9 and later
+        field_annotations = getattr(return_ann, '__annotations__', None) or getattr(return_ann, '_field_types', None)
         for field_name in return_ann._fields:
             type_struct = None
-            if hasattr(return_ann, '_field_types'):
-                type_struct = annotation_to_type_struct(return_ann._field_types.get(field_name, None))
+            if field_annotations:
+                type_struct = annotation_to_type_struct(field_annotations.get(field_name, None))
 
             output_name = _make_name_unique_by_adding_index(field_name, output_names, '_')
             output_names.add(output_name)