Use correct ignore field prefix in Python side
diff --git a/sdks/python/apache_beam/transforms/external.py b/sdks/python/apache_beam/transforms/external.py
index 77da49e..16840c4 100644
--- a/sdks/python/apache_beam/transforms/external.py
+++ b/sdks/python/apache_beam/transforms/external.py
@@ -153,7 +153,7 @@
   constructor and builder methods.
   """
 
-  IGNORED_ARG_FORMAT = 'arg%d'
+  IGNORED_ARG_FORMAT = 'ignore%d'
 
   def __init__(self, class_name):
     """
diff --git a/sdks/python/apache_beam/transforms/external_test.py b/sdks/python/apache_beam/transforms/external_test.py
index 9a3b7cf..8673ed5 100644
--- a/sdks/python/apache_beam/transforms/external_test.py
+++ b/sdks/python/apache_beam/transforms/external_test.py
@@ -431,7 +431,10 @@
     self._verify_row(
         payload_from_bytes.constructor_schema,
         payload_from_bytes.constructor_payload, {
-            'arg0': 'abc', 'arg1': 123, 'str_field': 'def', 'int_field': 456
+            'ignore0': 'abc',
+            'ignore1': 123,
+            'str_field': 'def',
+            'int_field': 456
         })
 
   def test_build_payload_with_constructor_method(self):
@@ -447,7 +450,10 @@
     self._verify_row(
         payload_from_bytes.constructor_schema,
         payload_from_bytes.constructor_payload, {
-            'arg0': 'abc', 'arg1': 123, 'str_field': 'def', 'int_field': 456
+            'ignore0': 'abc',
+            'ignore1': 123,
+            'str_field': 'def',
+            'int_field': 456
         })
 
   def test_build_payload_with_builder_methods(self):
@@ -464,7 +470,10 @@
     self._verify_row(
         payload_from_bytes.constructor_schema,
         payload_from_bytes.constructor_payload, {
-            'arg0': 'abc', 'arg1': 123, 'str_field': 'def', 'int_field': 456
+            'ignore0': 'abc',
+            'ignore1': 123,
+            'str_field': 'def',
+            'int_field': 456
         })
     self.assertEqual(2, len(payload_from_bytes.builder_methods))
     builder_method = payload_from_bytes.builder_methods[0]
@@ -473,9 +482,10 @@
 
     self._verify_row(
         builder_method.schema,
-        builder_method.payload, {
-            'arg0': 'abc1',
-            'arg1': 1234,
+        builder_method.payload,
+        {
+            'ignore0': 'abc1',
+            'ignore1': 1234,
             'str_field1': 'abc2',
             'int_field1': 2345
         })
@@ -485,9 +495,10 @@
     self.assertEqual('builder_method2', builder_method.name)
     self._verify_row(
         builder_method.schema,
-        builder_method.payload, {
-            'arg0': 'abc3',
-            'arg1': 3456,
+        builder_method.payload,
+        {
+            'ignore0': 'abc3',
+            'ignore1': 3456,
             'str_field2': 'abc4',
             'int_field2': 4567
         })