feat: add tuple preservation to AutoSerializer and 'pythonic' alias

src/cachekit/serializers/__init__.py

@@ -52,6 +52,7 @@ def _get_arrow_serializer() -> type:
 # This allows passing enable_integrity_checking parameter during instantiation
 SERIALIZER_REGISTRY = {
     "auto": AutoSerializer,  # Python-specific types (NumPy, pandas, datetime optimization)
+    "pythonic": AutoSerializer,  # Alias — preserves Python types (tuples, sets, frozensets, datetime, UUID)
     "default": StandardSerializer,  # Language-agnostic MessagePack for multi-language caches
     "std": StandardSerializer,  # Explicit StandardSerializer alias
     "arrow": None,  # Lazy-loaded: requires pyarrow from [data] extra
@@ -121,7 +122,7 @@ def get_serializer(name: str, enable_integrity_checking: bool = True) -> Seriali
             serializer_class = SERIALIZER_REGISTRY[name]
 
         # Instantiate with integrity checking configuration
-        if name in ("default", "std", "auto", "arrow", "orjson"):
+        if name in ("default", "std", "auto", "pythonic", "arrow", "orjson"):
             # All core serializers use enable_integrity_checking parameter
             serializer = serializer_class(enable_integrity_checking=enable_integrity_checking)
         else:

src/cachekit/serializers/auto_serializer.py

@@ -9,6 +9,7 @@
 - datetime/date/time (ISO-8601)
 - UUID (string representation)
 - set/frozenset (type-safe roundtrip)
+- tuple (recursive type-safe roundtrip)
 
 Uses MessagePack as the default format with graceful degradation for optional dependencies.
 
@@ -73,7 +74,7 @@
 
 CUSTOM_CLASS_ERROR_MESSAGE = (
     "AutoSerializer does not support custom classes. "
-    "Supported types: dict, list, str, int, float, bool, None, bytes, "
+    "Supported types: dict, list, tuple, str, int, float, bool, None, bytes, "
     "datetime, date, time, UUID, set, frozenset, NumPy arrays, pandas DataFrames.\n"
     "Options:\n"
     "  1. Convert to dict manually\n"
@@ -124,6 +125,26 @@ def _safe_hasattr(obj: Any, attr: str) -> bool:
         return False
 
 
+def _wrap_tuples(obj: Any) -> Any:
+    """Recursively wrap tuples in type markers before msgpack encoding.
+
+    Msgpack natively serializes tuples as arrays (same as lists), so the
+    ``default`` callback is never called for them. This pre-processor
+    converts tuples to ``{"__tuple__": True, "value": [...]}`` markers
+    that ``_auto_object_hook`` restores on deserialization.
+
+    Only affects tuples — all other types pass through unchanged and are
+    handled by msgpack's ``default`` callback (``_auto_default``).
+    """
+    if isinstance(obj, tuple):
+        return {"__tuple__": True, "value": [_wrap_tuples(x) for x in obj]}
+    if isinstance(obj, list):
+        return [_wrap_tuples(x) for x in obj]
+    if isinstance(obj, dict):
+        return {k: _wrap_tuples(v) for k, v in obj.items()}
+    return obj
+
+
 def _auto_default(obj: Any) -> Any:
     """Custom encoder for types not natively supported by MessagePack.
 
@@ -226,6 +247,14 @@ def _auto_object_hook(obj: Any) -> Any:
             except (ValueError, TypeError) as e:
                 raise SerializationError(f"Invalid UUID format in cached data: {value}") from e
 
+        if obj.get("__tuple__") is True:
+            if "value" not in obj:
+                raise SerializationError("Invalid tuple format: missing 'value' field in cached data")
+            value_list = obj["value"]
+            if not isinstance(value_list, list):
+                raise SerializationError(f"Invalid tuple format: expected list, got {type(value_list).__name__}")
+            return tuple(value_list)
+
         if obj.get("__set__") is True:
             if "value" not in obj:
                 raise SerializationError("Invalid set format: missing 'value' field in cached data")
@@ -748,6 +777,8 @@ def _deserialize_series(self, data) -> pd.Series:
 
     def _serialize_msgpack(self, obj: Any) -> bytes:
         """Serialize general object with MessagePack."""
+        # Pre-process tuples into markers (msgpack natively flattens them to lists)
+        obj = _wrap_tuples(obj)
         msgpack_data = msgpack.packb(obj, **self._msgpack_pack_opts)
 
         if self.enable_integrity_checking:

tests/unit/test_auto_serializer_new_types.py

@@ -1,4 +1,4 @@
-"""Unit tests for AutoSerializer new type support (UUID, set, frozenset).
+"""Unit tests for AutoSerializer new type support (UUID, set, frozenset, tuple).
 
 Tests:
 - UUID serialization roundtrip
@@ -559,3 +559,97 @@ def test_uuid_deterministic_serialization_property(self, uuid_list: list[UUID]):
         result1 = serializer.deserialize(bytes1)
         result2 = serializer.deserialize(bytes2)
         assert result1 == result2
+
+
+class TestAutoSerializerTuple:
+    """Test tuple preservation through AutoSerializer roundtrip."""
+
+    def test_simple_tuple_roundtrip(self):
+        serializer = AutoSerializer()
+        data = (1, 2, 3)
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result, tuple)
+        assert result == (1, 2, 3)
+
+    def test_nested_tuple_roundtrip(self):
+        serializer = AutoSerializer()
+        data = (1, (2, 3), (4, (5, 6)))
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result, tuple)
+        assert isinstance(result[1], tuple)
+        assert isinstance(result[2][1], tuple)
+        assert result == (1, (2, 3), (4, (5, 6)))
+
+    def test_empty_tuple_roundtrip(self):
+        serializer = AutoSerializer()
+        data = ()
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result, tuple)
+        assert result == ()
+
+    def test_tuple_in_dict(self):
+        serializer = AutoSerializer()
+        data = {"key": (1, 2), "other": "value"}
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result["key"], tuple)
+        assert result["key"] == (1, 2)
+
+    def test_tuple_in_list(self):
+        serializer = AutoSerializer()
+        data = [(1, 2), (3, 4)]
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result[0], tuple)
+        assert isinstance(result[1], tuple)
+
+    def test_tuple_with_set_and_datetime(self):
+        """Tuple containing other special types that use _auto_default."""
+        from datetime import datetime
+
+        serializer = AutoSerializer()
+        data = (1, {2, 3}, datetime(2025, 1, 1))
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result, tuple)
+        assert isinstance(result[1], set)
+        assert isinstance(result[2], datetime)
+
+    def test_list_preserved_as_list_not_tuple(self):
+        """Lists must stay as lists — only tuples get markers."""
+        serializer = AutoSerializer()
+        data = [1, 2, 3]
+        serialized, metadata = serializer.serialize(data)
+        result = serializer.deserialize(serialized, metadata)
+        assert isinstance(result, list)
+
+    def test_malformed_tuple_marker_missing_value(self):
+        """Malformed __tuple__ marker raises SerializationError."""
+        import msgpack
+
+        serializer = AutoSerializer(enable_integrity_checking=False)
+        bad_data = msgpack.packb({"__tuple__": True})
+        with pytest.raises(SerializationError, match="missing 'value' field"):
+            serializer.deserialize(bad_data)
+
+    def test_malformed_tuple_marker_wrong_value_type(self):
+        """__tuple__ marker with non-list value raises SerializationError."""
+        import msgpack
+
+        serializer = AutoSerializer(enable_integrity_checking=False)
+        bad_data = msgpack.packb({"__tuple__": True, "value": "not a list"})
+        with pytest.raises(SerializationError, match="expected list"):
+            serializer.deserialize(bad_data)
+
+
+class TestPythonicSerializerAlias:
+    """Test 'pythonic' alias for AutoSerializer."""
+
+    def test_pythonic_returns_auto_serializer(self):
+        from cachekit.serializers import get_serializer
+
+        s = get_serializer("pythonic")
+        assert isinstance(s, AutoSerializer)