[3.14] gh-142451: correctly copy HMAC attributes in HMAC.copy() (GH-142510) (#142698)

Partially cherry-picked from d3ef5ba34d
which ensures that the `block_size` attribute exists on the copy.

Lib/hmac.py

@@ -159,6 +159,7 @@ def copy(self):
         # Call __new__ directly to avoid the expensive __init__.
         other = self.__class__.__new__(self.__class__)
         other.digest_size = self.digest_size
+        other.block_size = self.block_size
         if self._hmac:
             other._hmac = self._hmac.copy()
             other._inner = other._outer = None

Lib/test/test_hmac.py

@@ -1076,6 +1076,15 @@ def test_properties(self):
         self.assertEqual(h.digest_size, self.digest_size)
         self.assertEqual(h.block_size, self.block_size)
 
+    def test_copy(self):
+        # Test a generic copy() and the attributes it exposes.
+        # See https://github.com/python/cpython/issues/142451.
+        h1 = self.hmac_new(b"my secret key", digestmod=self.digestname)
+        h2 = h1.copy()
+        self.assertEqual(h1.name, h2.name)
+        self.assertEqual(h1.digest_size, h2.digest_size)
+        self.assertEqual(h1.block_size, h2.block_size)
+
     def test_repr(self):
         # HMAC object representation may differ across implementations
         raise NotImplementedError

Misc/NEWS.d/next/Library/2025-12-14-10-00-23.gh-issue-142451._rkf2S.rst

@@ -0,0 +1,3 @@
+:mod:`hmac`: Ensure that the :attr:`HMAC.block_size <hmac.HMAC.block_size>`
+attribute is correctly copied by :meth:`HMAC.copy <hmac.HMAC.copy>`. Patch
+by Bénédikt Tran.