add discard()

docs/api/immutabledict.rst

@@ -1,5 +1,5 @@
 immutabledict
-======================
+=============
 
 .. autoclass:: immutabledict.immutabledict
     :exclude-members: items,keys,values

immutabledict/__init__.py

@@ -142,6 +142,21 @@ def update(self, _dict: Dict[_K, _V]) -> immutabledict[_K, _V]:
         new.update(_dict)
         return self.__class__(new)
 
+    def discard(self, key: _K) -> immutabledict[_K, _V]:
+        """
+        Return a new :class:`immutabledict` without the item at the given key, if present.
+
+        :param key: the key of the item you want to remove in the returned :class:`immutabledict`
+
+        :return: the new :class:`immutabledict` without the item at the given
+            key, or a reference to itself if the key is not present
+        """
+        # Based on the pyrsistent.PMap.discard() API
+        if key not in self:
+            return self
+
+        return self.delete(key)
+
 
 class ImmutableOrderedDict(immutabledict[_K, _V]):
     """

tests/test_immutabledict.py

@@ -235,6 +235,18 @@ def test_set_delete_update(self) -> None:
         # Make sure d doesn't change
         assert d == immutabledict(a=1, b=2) == dict(a=1, b=2)
 
+    def test_discard(self) -> None:
+        d: immutabledict[str, int] = immutabledict(a=1, b=2)
+
+        # Key present
+        assert d.discard("a") == immutabledict(b=2) == {"b": 2}
+        assert hash(d.discard("a")) != hash(d)
+
+        # Key not present
+        assert d.discard("c") == d == {"a": 1, "b": 2}
+        assert hash(d.discard("c")) == hash(d)
+        assert d.discard("c") is d
+
     def test_new_kwargs(self) -> None:
         immutable_dict: immutabledict[str, int] = immutabledict(a=1, b=2)
         assert immutable_dict == {"a": 1, "b": 2} == dict(a=1, b=2)