Use consistent method of determining AWS Partition from a region (#2899)

Co-authored-by: Andrew Cristina <[email protected]>

Author: acristin

integration/helpers/base_test.py

@@ -95,7 +95,6 @@ def setUpClass(cls):
         cls.code_dir = Path(cls.resources_dir, "code")
         cls.session = boto3.session.Session()
         cls.my_region = cls.session.region_name
-        cls.partition = cls.session.get_partition_for_region(cls.my_region)
         cls.client_provider = ClientProvider()
         cls.file_to_s3_uri_map = read_test_config_file("file_to_s3_map_modified.json")
         cls.code_key_to_file = read_test_config_file("code_key_to_file_map.json")

samtranslator/region_configuration.py

@@ -52,6 +52,6 @@ def is_service_supported(cls, service, region=None):  # type: ignore[no-untyped-
                     raise NoRegionFound("AWS Region cannot be found")
 
         # check if the service is available in region
-        partition = session.get_partition_for_region(region)
+        partition = ArnGenerator.get_partition_name(region)
         available_regions = session.get_available_regions(service, partition_name=partition)
         return region in available_regions