Add get_checksum_algorithm_key

3 files changed, 20 insertions, 2 deletions

diff --git a/obnamlib/__init__.py b/obnamlib/__init__.py
index e1d58c53..48ebe95e 100644
--- a/obnamlib/__init__.py
+++ b/obnamlib/__init__.py
@@ -161,6 +161,7 @@ from .checksummer import (
     checksum_algorithms,
     get_checksum_algorithm,
     get_checksum_algorithm_name,
+    get_checksum_algorithm_key,
 )
 
 from .whole_file_checksummer import WholeFileCheckSummer
diff --git a/obnamlib/checksummer.py b/obnamlib/checksummer.py
index f1c8e62f..c420cf6b 100644
--- a/obnamlib/checksummer.py
+++ b/obnamlib/checksummer.py
@@ -48,6 +48,13 @@ def get_checksum_algorithm_name(wanted_key):
         algorithm=obnamlib.repo_key_name(wanted_key))
 
 
+def get_checksum_algorithm_key(wanted_name):
+    for name, key, _ in _algorithm_list:
+        if name == wanted_name:
+            return key
+    raise UnknownChecksumAlgorithm(algorithm=wanted_name)
+
+
 class UnknownChecksumAlgorithm(obnamlib.ObnamError):
 
     msg = 'Unknown checksum algorithm {algorithm}.'
diff --git a/obnamlib/checksummer_tests.py b/obnamlib/checksummer_tests.py
index a6c345f4..db4832cd 100644
--- a/obnamlib/checksummer_tests.py
+++ b/obnamlib/checksummer_tests.py
@@ -31,16 +31,26 @@ class TestGetChecksummer(unittest.TestCase):
         self.assertRaises(
             obnamlib.ObnamError, obnamlib.get_checksum_algorithm, 'unknown')
 
-    def test_knows_file_key_for_sha512(self):
+    def test_finds_name_from_file_key_for_sha512(self):
         self.assertEqual(
             obnamlib.get_checksum_algorithm_name(obnamlib.REPO_FILE_SHA512),
             'sha512')
 
-    def test_raises_error_if_algorithm_is_unknown_for_key(self):
+    def test_raises_error_if_algorithm_name_is_unknown_for_key(self):
         self.assertRaises(
             obnamlib.ObnamError,
             obnamlib.get_checksum_algorithm_name, -1)
 
+    def test_finds_file_key_from_name_for_sha512(self):
+        self.assertEqual(
+            obnamlib.get_checksum_algorithm_key('sha512'),
+            obnamlib.REPO_FILE_SHA512)
+
+    def test_raises_error_if_algorithm_key_is_unknown_for_name(self):
+        self.assertRaises(
+            obnamlib.ObnamError,
+            obnamlib.get_checksum_algorithm_key, 'unknown')
+
     def test_returns_working_sha512(self):
         summer = obnamlib.get_checksum_algorithm('sha512')
         summer.update('hello, world')