Merge pull request #244 from spacether/feat_adds_covariance

Adds covariant true to key type

immutabledict/__init__.py

@@ -6,7 +6,7 @@
 __version__ = "2.2.5"
 
 _K = TypeVar("_K")
-_V = TypeVar("_V")
+_V = TypeVar("_V", covariant=True)
 
 
 class immutabledict(Mapping[_K, _V]):
@@ -35,8 +35,8 @@ def __getitem__(self, key: _K) -> _V:
     def __contains__(self, key: object) -> bool:
         return key in self._dict
 
-    def copy(self, **add_or_replace: _V) -> immutabledict[_K, _V]:
-        return self.__class__(self, **add_or_replace)
+    def copy(self) -> immutabledict[_K, _V]:
+        return self.__class__(self)
 
     def __iter__(self) -> Iterator[_K]:
         return iter(self._dict)

tests/test_immutabledict.py

@@ -4,6 +4,10 @@
 
 
 class TestImmutableDict:
+    def test_covariance(self):
+        assert immutabledict.__parameters__[0].__covariant__ is False
+        assert immutabledict.__parameters__[1].__covariant__ is True
+
     def test_cannot_assign_value(self):
         with pytest.raises(AttributeError):
             immutabledict().setitem("key", "value")
@@ -41,6 +45,7 @@ def test_copy(self):
         original = immutabledict({"a": "value"})
         copy = original.copy()
         assert original == copy
+        assert id(original) != id(copy)
 
     def test_iter(self):
         immutable_dict = immutabledict({"a": "value", "b": "other_value"})