chore: deal with adding new partitions for arn generation (#3571)

samtranslator/translator/arn_generator.py

@@ -17,16 +17,20 @@ def _get_region_from_session() -> str:
 def _region_to_partition(region: str) -> str:
     # setting default partition to aws, this will be overwritten by checking the region below
     region_string = region.lower()
-    if region_string.startswith("cn-"):
-        return "aws-cn"
-    if region_string.startswith("us-iso-"):
-        return "aws-iso"
-    if region_string.startswith("us-isob"):
-        return "aws-iso-b"
-    if region_string.startswith("us-gov"):
-        return "aws-us-gov"
-    if region_string.startswith("eu-isoe"):
-        return "aws-iso-e"
+    region_to_partition_map = {
+        "cn-": "aws-cn",
+        "us-iso-": "aws-iso",
+        "us-isob": "aws-iso-b",
+        "us-gov": "aws-us-gov",
+        "eu-isoe": "aws-iso-e",
+    }
+    for key, value in region_to_partition_map.items():
+        if region_string.startswith(key):
+            return value
+
+    # Using the ${AWS::Partition} placeholder so that we don't have to add new regions to the static list above
+    if "iso" in region_string:
+        return "${AWS::Partition}"
 
     return "aws"
 

tests/translator/test_arn_generator.py

@@ -10,7 +10,15 @@ def setUp(self):
         ArnGenerator.BOTO_SESSION_REGION_NAME = None
 
     @parameterized.expand(
-        [("us-east-1", "aws"), ("cn-east-1", "aws-cn"), ("us-gov-west-1", "aws-us-gov"), ("US-EAST-1", "aws")]
+        [
+            ("us-east-1", "aws"),
+            ("cn-east-1", "aws-cn"),
+            ("us-gov-west-1", "aws-us-gov"),
+            ("us-isob-east-1", "aws-iso-b"),
+            ("eu-isoe-west-1", "aws-iso-e"),
+            ("US-EAST-1", "aws"),
+            ("us-isof-east-1", "${AWS::Partition}"),
+        ]
     )
     def test_get_partition_name(self, region, expected):
         actual = ArnGenerator.get_partition_name(region)