Add UnknownRegionError and additional tests

botocore/exceptions.py

@@ -64,6 +64,16 @@ class UnknownServiceError(DataNotFoundError):
         "Unknown service: '{service_name}'. Valid service names are: "
         "{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):
     """

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}'
@@ -135,6 +137,13 @@ def construct_endpoint(self, service_name, region_name=None, partition_name=None
                 return result
             return None
 
+        # Iterate over each partition until a match is found.
+        for partition in self._endpoint_data['partitions']:
+            result = self._endpoint_for_partition(
+                partition, service_name, region_name)
+            if result:
+                return result
+
     def get_partition_for_region(self, region_name):
         for partition in self._endpoint_data['partitions']:
             if region_name in partition['regions']:
@@ -143,14 +152,10 @@ def get_partition_for_region(self, region_name):
                 continue
             if re.compile(partition['regionRegex']).match(region_name):
                 return partition['partition']
-        raise ValueError('Invalid region name: {0}'.format(region_name))
-
-        # Iterate over each partition until a match is found.
-        for partition in self._endpoint_data['partitions']:
-            result = self._endpoint_for_partition(
-                partition, service_name, region_name)
-            if result:
-                return result
+        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

tests/unit/test_session.py

@@ -384,10 +384,19 @@ 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(ValueError):
+        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):
         self.session.user_agent_name = 'something-else'