Properly propagate schemas of Beam YAML Partition transform.

Author: robertwb

sdks/python/apache_beam/yaml/yaml_mapping.py

@@ -814,6 +814,8 @@ def split(element):
     mapping_transform = mapping_transform.with_outputs(*output_set)
   splits = pcoll | mapping_transform.with_input_types(T).with_output_types(T)
   result = {out: getattr(splits, out) for out in output_set}
+  for out in result.values():
+    out.element_type = pcoll.element_type
   if error_output:
     result[error_output] = result[error_output] | map_errors_to_standard_format(
         pcoll.element_type)

sdks/python/apache_beam/yaml/yaml_mapping_test.py

@@ -212,6 +212,7 @@ def test_partition(self):
             language: python
             outputs: [even, odd]
           ''')
+      self.assertEqual(result['even'].element_type, elements.element_type)
       assert_that(
           result['even'] | beam.Map(lambda x: x.element),
           equal_to(['banana', 'orange']),