python · blhsing · May 21, 2026 · May 21, 2026 · May 21, 2026
diff --git a/Doc/library/difflib.rst b/Doc/library/difflib.rst
@@ -40,6 +40,15 @@ diffs. For comparing directories and files, see also, the :mod:`filecmp` module.
    complicated way on how many elements the sequences have in common; best case
    time is linear.
 
+   .. impl-detail::
+
+      On CPython, the :class:`SequenceMatcher` class is implemented in C for
+      speed.  The pure-Python reference implementation remains available as
+      :mod:`!_pydifflib` for alternative Python implementations.  Output is
+      bit-identical between the two implementations, including tie-breaks;
+      typical workloads run 5--25x faster than the pure-Python version, with
+      character/byte sequences seeing the largest gains.
+
    **Automatic junk heuristic:** :class:`SequenceMatcher` supports a heuristic that
    automatically treats certain sequence items as junk. The heuristic counts how many
    times each individual item appears in the sequence. If an item's duplicates (after

diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h
@@ -302,12 +302,14 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(adobe)
         STRUCT_FOR_ID(after_in_child)
         STRUCT_FOR_ID(after_in_parent)
+        STRUCT_FOR_ID(ahi)
         STRUCT_FOR_ID(alias)
         STRUCT_FOR_ID(align)
         STRUCT_FOR_ID(all)
         STRUCT_FOR_ID(all_interpreters)
         STRUCT_FOR_ID(all_threads)
         STRUCT_FOR_ID(allow_code)
+        STRUCT_FOR_ID(alo)
         STRUCT_FOR_ID(alphabet)
         STRUCT_FOR_ID(any)
         STRUCT_FOR_ID(append)
@@ -322,13 +324,16 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(athrow)
         STRUCT_FOR_ID(attribute)
         STRUCT_FOR_ID(autocommit)
+        STRUCT_FOR_ID(autojunk)
         STRUCT_FOR_ID(backtick)
         STRUCT_FOR_ID(base)
         STRUCT_FOR_ID(before)
+        STRUCT_FOR_ID(bhi)
         STRUCT_FOR_ID(big)
         STRUCT_FOR_ID(binary_form)
         STRUCT_FOR_ID(bit_offset)
         STRUCT_FOR_ID(bit_size)
+        STRUCT_FOR_ID(blo)
         STRUCT_FOR_ID(block)
         STRUCT_FOR_ID(blocking)
         STRUCT_FOR_ID(bound)
@@ -573,6 +578,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(is_struct)
         STRUCT_FOR_ID(isatty)
         STRUCT_FOR_ID(isinstance)
+        STRUCT_FOR_ID(isjunk)
         STRUCT_FOR_ID(isoformat)
         STRUCT_FOR_ID(isolation_level)
         STRUCT_FOR_ID(istext)

diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h