[GitHub] [beam] chamikaramj commented on a diff in pull request #23047: Expand Python cross language docs.

[GitBox <gi...@apache.org>]

chamikaramj commented on code in PR #23047:
URL: https://github.com/apache/beam/pull/23047#discussion_r974312230


##########
website/www/site/content/en/documentation/programming-guide.md:
##########
@@ -7364,13 +7370,37 @@ When an SDK-specific wrapper isn't available, you will have to access the cross-
             | beam.ExternalTransform(
                 TEST_PREFIX_URN,
                 ImplicitSchemaPayloadBuilder({'data': u'0'}),
-                <Address of expansion service>))
+                <expansion service>))
         assert_that(res, equal_to(['0a', '0b']))
     ```
 
     For additional examples, see [addprefix.py](https://github.com/apache/beam/blob/master/examples/multi-language/python/addprefix.py) and [javacount.py](https://github.com/apache/beam/blob/master/examples/multi-language/python/javacount.py).
 
-4. After the job has been submitted to the Beam runner, shut down the expansion service by terminating the expansion service process.
+4. After the job has been submitted to the Beam runner, shut down any manually started expansion services by terminating the expansion service process.
+
+**Using the JavaExternalTransform class**
+
+Python has the ability to invoke Java-defined transforms via [proxy objects](https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.external.html#apache_beam.transforms.external.JavaExternalTransform)
+as if they were Python transforms.
+These are invoked as follows
+
+    ```py
+    MyJavaTransform = beam.JavaExternalTransform('fully.qualified.ClassName', classpath=[jars])
+
+    with pipeline as p:
+        res = (
+            p
+            | beam.Create(['a', 'b']).with_output_types(unicode)
+            | MyJavaTransform(javaConstructorArg, ...).builderMethod(...)
+        assert_that(res, equal_to(['0a', '0b']))
+    ```
+
+Python's `getattr` method can be used if the method names in java are reserved

Review Comment:
   We should also mention the withExtraPackages() method here.



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