Remove sentinel-value dependency

I did not like this how this library doesn't use pickle singletons

I'll use classes for now since those can switch to something better later

Author: HexDecimal

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Removed dependency on `sentinel-value`.
+
 ## [5.4.2] - 2025-11-28
 
 ### Removed

pyproject.toml

@@ -21,7 +21,6 @@ requires-python = ">=3.10"
 dependencies = [
     "attrs >=23.1.0",
     "cattrs >=23.1.2",
-    "sentinel-value >=1.0.0",
     "typing-extensions >=4.13.1",
 ]
 

tcod/ecs/constants.py

@@ -2,9 +2,18 @@
 
 from __future__ import annotations
 
-from typing import Final
 
-from sentinel_value import sentinel
+class _IgnoreSetState(type):
+    def __setstate__(cls, _state: object) -> None:
+        """Ignore setstate on outdated sentinel-value pickle data."""
 
-IsA: Final = sentinel("IsA")
-"""The default is-a relationship tag used for entity inheritance."""
+
+class IsA(metaclass=_IgnoreSetState):
+    """The default is-a relationship tag used for entity inheritance."""
+
+    def __new__(cls: type[IsA], *_args: object) -> type[IsA]:  # type: ignore[misc]
+        """Return own type instead of instance, for outdated sentinel-value pickle data."""
+        return cls
+
+
+_sentinel_IsA = IsA  # Compatibility with sentinel-value, deprecated since 5.4  # noqa: N816

tests/test_ecs.py

@@ -301,3 +301,10 @@ def test_type_form() -> None:
     world[None].components[TupleKey] = (1, 2)
     x, y = world[None].components[TupleKey]
     assert (x, y) == (1, 2)
+
+
+PICKLED_ISA = b"\x80\x03ctcod.ecs.constants\n_sentinel_IsA\nq\x00X\x12\x00\x00\x00tcod.ecs.constantsq\x01X\x03\x00\x00\x00IsAq\x02\x86q\x03\x81q\x04}q\x05(X\r\x00\x00\x00instance_nameq\x06h\x02X\x0b\x00\x00\x00module_nameq\x07h\x01X\x0e\x00\x00\x00qualified_nameq\x08X\x16\x00\x00\x00tcod.ecs.constants.IsAq\tub."  # cspell: disable-line
+
+
+def test_unpickle_is_a() -> None:
+    assert pickle.loads(PICKLED_ISA) is tcod.ecs.IsA  # noqa: S301