Find the partition of a region

.changes/next-release/enhancement-Session-66470.json

@@ -0,0 +1,5 @@
+{
+  "type": "enhancement",
+  "category": "Session",
+  "description": "Added `get_partition_for_region` allowing partition lookup by region name."
+}

botocore/exceptions.py

@@ -65,6 +65,17 @@ class UnknownServiceError(DataNotFoundError):
         "{known_service_names}")
 
 
+class UnknownRegionError(BotoCoreError):
+    """Raised when trying to load data for an unknown region.
+
+    :ivar region_name: The name of the unknown region.
+
+    """
+    fmt = (
+        "Unknown region: '{region_name}'. {error_msg}"
+    )
+
+
 class ApiVersionNotFoundError(BotoCoreError):
     """
     The data associated with either the API version or a compatible one

botocore/regions.py

@@ -19,7 +19,9 @@
 import logging
 import re
 
-from botocore.exceptions import NoRegionError
+from botocore.exceptions import (
+    NoRegionError, UnknownRegionError
+)
 
 LOG = logging.getLogger(__name__)
 DEFAULT_URI_TEMPLATE = '{service}.{region}.{dnsSuffix}'
@@ -142,6 +144,15 @@ def construct_endpoint(self, service_name, region_name=None, partition_name=None
             if result:
                 return result
 
+    def get_partition_for_region(self, region_name):
+        for partition in self._endpoint_data['partitions']:
+            if self._region_match(partition, region_name):
+                return partition['partition']
+        raise UnknownRegionError(
+            region_name=region_name,
+            error_msg='No partition found for provided region_name.'
+        )
+
     def _endpoint_for_partition(
         self, partition, service_name, region_name, force_partition=False
     ):

botocore/session.py

@@ -886,6 +886,19 @@ def get_available_partitions(self):
         resolver = self._get_internal_component('endpoint_resolver')
         return resolver.get_available_partitions()
 
+    def get_partition_for_region(self, region_name):
+        """Lists the partition name of a particular region.
+
+        :type region_name: string
+        :param region_name: Name of the region to list partition for (e.g.,
+             us-east-1).
+
+        :rtype: string
+        :return: Returns the respective partition name (e.g., aws).
+        """
+        resolver = self._get_internal_component('endpoint_resolver')
+        return resolver.get_partition_for_region(region_name)
+
     def get_available_regions(self, service_name, partition_name='aws',
                               allow_non_regional=False):
         """Lists the region and endpoint names of a particular partition.

tests/unit/test_session.py

@@ -380,6 +380,22 @@ def test_provides_empty_list_for_unknown_service_regions(self):
         regions = self.session.get_available_regions('__foo__')
         self.assertEqual([], regions)
 
+    def test_provides_correct_partition_for_region(self):
+        partition = self.session.get_partition_for_region('us-west-2')
+        self.assertEqual(partition, 'aws')
+
+    def test_provides_correct_partition_for_region_regex(self):
+        partition = self.session.get_partition_for_region('af-south-99')
+        self.assertEqual(partition, 'aws')
+
+    def test_provides_correct_partition_for_region_non_default(self):
+        partition = self.session.get_partition_for_region('cn-north-1')
+        self.assertEqual(partition, 'aws-cn')
+
+    def test_raises_exception_for_invalid_region(self):
+        with self.assertRaises(botocore.exceptions.UnknownRegionError):
+            self.session.get_partition_for_region('no-good-1')
+
 
 class TestSessionUserAgent(BaseSessionTest):
     def test_can_change_user_agent_name(self):