Issue #18742: Rework the internal hashlib construtor to pave the road for ABCs.

1 files changed, 20 insertions, 21 deletions

diff --git a/Lib/hashlib.py b/Lib/hashlib.py
index 56a9360..77673f0 100644
--- a/Lib/hashlib.py
+++ b/Lib/hashlib.py
@@ -64,43 +64,42 @@ __all__ = __always_supported + ('new', 'algorithms_guaranteed',
                                 'algorithms_available', 'pbkdf2_hmac')
 
 
+__builtin_constructor_cache = {}
+
 def __get_builtin_constructor(name):
+    cache = __builtin_constructor_cache
+    constructor = cache.get(name)
+    if constructor is not None:
+        return constructor
     try:
         if name in ('SHA1', 'sha1'):
             import _sha1
-            return _sha1.sha1
+            cache['SHA1'] = cache['sha1'] = _sha1.sha1
         elif name in ('MD5', 'md5'):
             import _md5
-            return _md5.md5
+            cache['MD5'] = cache['md5'] = _md5.md5
         elif name in ('SHA256', 'sha256', 'SHA224', 'sha224'):
             import _sha256
-            bs = name[3:]
-            if bs == '256':
-                return _sha256.sha256
-            elif bs == '224':
-                return _sha256.sha224
+            cache['SHA224'] = cache['sha224'] = _sha256.sha224
+            cache['SHA256'] = cache['sha256'] = _sha256.sha256
         elif name in ('SHA512', 'sha512', 'SHA384', 'sha384'):
             import _sha512
-            bs = name[3:]
-            if bs == '512':
-                return _sha512.sha512
-            elif bs == '384':
-                return _sha512.sha384
+            cache['SHA384'] = cache['sha384'] = _sha512.sha384
+            cache['SHA512'] = cache['sha512'] = _sha512.sha512
         elif name in {'sha3_224', 'sha3_256', 'sha3_384', 'sha3_512',
                       'SHA3_224', 'SHA3_256', 'SHA3_384', 'SHA3_512'}:
             import _sha3
-            bs = name[5:]
-            if bs == '224':
-                return _sha3.sha3_224
-            elif bs == '256':
-                return _sha3.sha3_256
-            elif bs == '384':
-                return _sha3.sha3_384
-            elif bs == '512':
-                return _sha3.sha3_512
+            cache['SHA3_224'] = cache['sha3_224'] = _sha3.sha3_224
+            cache['SHA3_256'] = cache['sha3_256'] = _sha3.sha3_256
+            cache['SHA3_384'] = cache['sha3_384'] = _sha3.sha3_384
+            cache['SHA3_512'] = cache['sha3_512'] = _sha3.sha3_512
     except ImportError:
         pass  # no extension module, this hash is unsupported.
 
+    constructor = cache.get(name)
+    if constructor is not None:
+        return constructor
+
     raise ValueError('unsupported hash type ' + name)