set update delete

constantdict/__init__.py

@@ -77,10 +77,28 @@ def __reduce__(self) -> str | tuple[Any, ...]:
         # which would raise an exception in constantdict.
         return (self.__class__, (dict(self),))
 
+    def set(self, key: K, val: Any) -> constantdict[K, V]:
+        """Return a new :class:`constantdict` with the item at *key* set to *val*."""
+        new = dict(self)
+        new[key] = val
+        return self.__class__(new)
+
+    def delete(self, key: K) -> constantdict[K, V]:
+        """Return a new :class:`constantdict` without the item at the given key."""
+        new = dict(self)
+        del new[key]
+        return self.__class__(new)
+
+    def update(self,  # type: ignore[override]
+               _dict: Dict[K, V]) -> constantdict[K, V]:
+        """Return a new :class:`constantdict` with updated items from *_dict*."""
+        new = dict(self)
+        new.update(_dict)
+        return self.__class__(new)
+
     __delitem__ = _del_attr
     __setitem__ = _del_attr
     clear = _del_attr
     popitem = _del_attr  # type: ignore[assignment]
     pop = _del_attr  # type: ignore[assignment]
     setdefault = _del_attr  # type: ignore[assignment]
-    update = _del_attr

test/test_constantdict.py

@@ -1,5 +1,7 @@
 from typing import Any
 
+import pytest
+
 from constantdict import constantdict
 
 
@@ -13,3 +15,24 @@ def test_fromkeys() -> None:
     cd: constantdict[Any, Any] = constantdict.fromkeys(["a", "b", "c"])
     assert cd == {"a": None, "b": None, "c": None}
     assert cd == dict.fromkeys(["a", "b", "c"])
+
+
+def test_set_delete_update() -> None:
+    d: constantdict[str, int] = constantdict(a=1, b=2)
+
+    assert d.set("a", 10) == constantdict(a=10, b=2) == dict(a=10, b=2)  # noqa: C408
+    assert d.delete("a") == constantdict(b=2) == dict(b=2)  # noqa: C408
+
+    with pytest.raises(KeyError):
+        d.delete("c")
+
+    assert d.update({"a": 3}) == constantdict(a=3, b=2) == {"a": 3, "b": 2}
+
+    assert (
+        d.update({"c": 17})
+        == constantdict(a=1, b=2, c=17)
+        == {"a": 1, "b": 2, "c": 17}
+    )
+
+    # Make sure 'd' has not changed
+    assert d == constantdict(a=1, b=2) == {"a": 1, "b": 2}