PEP 466: backport hashlib algorithm constants (closes #21307)

2 files changed, 20 insertions, 3 deletions

diff --git a/Lib/hashlib.py b/Lib/hashlib.py
index 6d69ad2..4a411bc 100644
--- a/Lib/hashlib.py
+++ b/Lib/hashlib.py
@@ -15,8 +15,9 @@ than using new():
 
 md5(), sha1(), sha224(), sha256(), sha384(), and sha512()
 
-More algorithms may be available on your platform but the above are
-guaranteed to exist.
+More algorithms may be available on your platform but the above are guaranteed
+to exist.  See the algorithms_guaranteed and algorithms_available attributes
+to find out what algorithm names can be passed to new().
 
 NOTE: If you want the adler32 or crc32 hash functions they are available in
 the zlib module.
@@ -58,9 +59,14 @@ More condensed:
 # always available algorithm is added.
 __always_supported = ('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')
 
+algorithms_guaranteed = set(__always_supported)
+algorithms_available = set(__always_supported)
+
 algorithms = __always_supported
 
-__all__ = __always_supported + ('new', 'algorithms', 'pbkdf2_hmac')
+__all__ = __always_supported + ('new', 'algorithms_guaranteed',
+                                'algorithms_available', 'algorithms',
+                                'pbkdf2_hmac')
 
 
 def __get_builtin_constructor(name):
@@ -128,6 +134,8 @@ try:
     import _hashlib
     new = __hash_new
     __get_hash = __get_openssl_constructor
+    algorithms_available = algorithms_available.union(
+        _hashlib.openssl_md_meth_names)
 except ImportError:
     new = __py_new
     __get_hash = __get_builtin_constructor
diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index 3fc172f..76be461 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -109,6 +109,15 @@ class HashLibTestCase(unittest.TestCase):
             tuple([_algo for _algo in self.supported_hash_names if
                                                 _algo.islower()]))
 
+    def test_algorithms_guaranteed(self):
+        self.assertEqual(hashlib.algorithms_guaranteed,
+            set(_algo for _algo in self.supported_hash_names
+                  if _algo.islower()))
+
+    def test_algorithms_available(self):
+        self.assertTrue(set(hashlib.algorithms_guaranteed).
+                            issubset(hashlib.algorithms_available))
+
     def test_unknown_hash(self):
         self.assertRaises(ValueError, hashlib.new, 'spam spam spam spam spam')
         self.assertRaises(TypeError, hashlib.new, 1)