Improve Iterator error message (#23972)

apache · Nov 4, 2022 · 1563b97 · 1563b97
1 parent 7da182a
commit 1563b97
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/sdks/python/apache_beam/transforms/core.py b/sdks/python/apache_beam/transforms/core.py
@@ -843,7 +843,9 @@ def _get_element_type_from_return_annotation(method, input_type):
     else:
       raise TypeError(
           "Expected Iterator in return type annotation for "
-          f"{method!r}, did you mean Iterator[{return_type}]?")
+          f"{method!r}, did you mean Iterator[{return_type}]? Note Beam DoFn "
+          "process and process_batch methods are expected to produce "
+          "generators - they should 'yield' rather than 'return'.")
 
   def get_output_batch_type(
       self, input_element_type