Add FrozenSet field

RELEASES.rst

@@ -6,6 +6,7 @@ Releases
 
 *Unreleased*
 
+- Add ``FrozenSet`` field.
 - Add ``Deque`` field.
 - Add ``default`` keyword argument to ``Field``. (`#111`_)
 - Fix bug in ``Uuid.normalize()``.

src/serde/fields.py

@@ -913,6 +913,28 @@ def __init__(self, key=None, value=None, **kwargs):
         self.value = _resolve_to_field_instance(value)
 
 
+class FrozenSet(_Container):
+    """
+    This field represents the built-in `frozenset` type.
+
+    Each element is serialized, deserialized, normalized and validated with the
+    specified element type. The element type can be specified using `Field`
+    classes, `Field` instances, `~serde.Model` classes, or built-in types that
+    have a corresponding field type in this library.
+
+    Args:
+        element: the `Field` class or instance for elements in the `Set`.
+        **kwargs: keyword arguments for the `Field` constructor.
+    """
+
+    def __init__(self, element=None, **kwargs):
+        """
+        Create a new `FrozenSet`.
+        """
+        super(FrozenSet, self).__init__(frozenset, **kwargs)
+        self.element = _resolve_to_field_instance(element)
+
+
 class List(_Container):
     """
     This field represents the built-in `list` type.

tests/test_fields.py

@@ -28,6 +28,7 @@
     Dict,
     Field,
     Float,
+    FrozenSet,
     Instance,
     Int,
     List,
@@ -950,6 +951,79 @@ def test___init___options(self):
         assert field.validators == [None]
 
 
+class TestFrozenSet:
+    def test___init___basic(self):
+        # Construct a basic FrozenSet and check values are set correctly.
+        field = FrozenSet()
+        assert field.element == Field()
+        assert field.validators == []
+
+    def test___init___options(self):
+        # Construct a FrozenSet with extra options and make sure values are passed to
+        # Field.
+        field = FrozenSet(element=Int, validators=[None])
+        assert field.element == Int()
+        assert field.validators == [None]
+
+    def test_serialize(self):
+        # A FrozenSet should serialize values based on the element Field.
+        field = FrozenSet(element=Reversed)
+        assert field.serialize(frozenset({'test', 'hello'})) == frozenset(
+            {'tset', 'olleh'}
+        )
+
+    def test_serialize_extra(self):
+        # A FrozenSet should serialize values based on the element Field.
+        field = FrozenSet(element=Field(serializers=[lambda x: x[::-1]]))
+        assert field.serialize(frozenset({'test', 'hello'})) == frozenset(
+            {'tset', 'olleh'}
+        )
+
+    def test_deserialize(self):
+        # A FrozenSet should deserialize values based on the element Field.
+        field = FrozenSet(element=Reversed)
+        assert field.deserialize(frozenset({'tset', 'olleh'})) == frozenset(
+            {'test', 'hello'}
+        )
+
+    def test_deserialize_extra(self):
+        # A FrozenSet should deserialize values based on the element Field.
+        field = FrozenSet(element=Field(deserializers=[lambda x: x[::-1]]))
+        assert field.deserialize(frozenset({'tset', 'olleh'})) == frozenset(
+            {'test', 'hello'}
+        )
+
+    def test_normalize(self):
+        # A FrozenSet should normalize values based on the element Field.
+        field = FrozenSet(element=Field)
+        assert field.normalize(frozenset({'test', 'hello'})) == frozenset(
+            {'test', 'hello'}
+        )
+
+    def test_normalize_extra(self):
+        # A FrozenSet should normalize values based on the element Field.
+        field = FrozenSet(element=Field(normalizers=[lambda x: x[::-1]]))
+        assert field.normalize(frozenset({'tset', 'olleh'})) == frozenset(
+            {'test', 'hello'}
+        )
+
+    def test_validate(self):
+        # A FrozenSet should validate values based on the element Field.
+        field = FrozenSet(element=Int)
+        field.validate(frozenset({0, 1, 2, 3, 4}))
+
+        with raises(ValidationError):
+            field.validate(frozenset({'1', '2', 'a', 'string'}))
+
+    def test_validate_extra(self):
+        # A FrozenSet should validate values based on the element Field.
+        field = FrozenSet(element=Field(validators=[validators.Between(10, 10)]))
+        field.validate(frozenset({10, 10, 10}))
+
+        with raises(ValidationError):
+            field.validate(frozenset({10, 11, 12, 13}))
+
+
 class TestList:
     def test___init___basic(self):
         # Construct a basic List and check values are set correctly.