Merge pull request #58 from trollboy/Literals_support

@robotoer's changes to support literal types

Author: necaris

graphene_pydantic/converters.py

@@ -266,6 +266,10 @@ def convert_generic_python_type(
         return convert_union_type(
             type_, field, registry, parent_type=parent_type, model=model
         )
+    elif origin == T.Literal:
+        return convert_literal_type(
+            type_, field, registry, parent_type=parent_type, model=model
+        )
     elif (
         origin
         in (
@@ -332,3 +336,37 @@ def convert_union_type(
         construct_union_class_name(inner_types), (Union,), {"Meta": internal_meta_cls}
     )
     return union_cls
+
+def convert_literal_type(
+    type_: T.Type,
+    field: ModelField,
+    registry: Registry,
+    parent_type: T.Type = None,
+    model: T.Type[BaseModel] = None,
+):
+    """
+    Convert an annotated Python Literal type into a Graphene Scalar or Union of Scalars.
+    """
+    inner_types = type_.__args__
+    # Here we'll expand the subtypes of this Literal into a corresponding more
+    # general scalar type.
+    scalar_types = {
+        type(x)
+        for x in inner_types
+        if x != NONE_TYPE
+    }
+    graphene_scalar_types = [
+        convert_pydantic_type(x, field, registry, parent_type=parent_type, model=model)
+        for x in scalar_types
+    ]
+
+    # If we only have a single type, we don't need to create a union.
+    if len(graphene_scalar_types) == 1:
+        return graphene_scalar_types[0]
+
+    internal_meta_cls = type("Meta", (), {"types": graphene_scalar_types})
+
+    union_cls = type(
+        construct_union_class_name(scalar_types), (Union,), {"Meta": internal_meta_cls}
+    )
+    return union_cls

tests/test_converters.py

@@ -74,6 +74,19 @@ def test_union():
     assert field.default_value == 5.0
     assert field.type.__name__.startswith("UnionOf")
 
+def test_literal():
+    field = _convert_field_from_spec("attr", (T.Literal['literal1', 'literal2', 3], 3))
+    assert issubclass(field.type, graphene.Union)
+    assert field.default_value == 3
+    assert field.type.__name__.startswith("UnionOf")
+
+
+def test_literal_singleton():
+    field = _convert_field_from_spec("attr", (T.Literal['literal1'], 'literal1'))
+    assert issubclass(field.type, graphene.String)
+    assert field.default_value == 'literal1'
+    assert field.type == graphene.String
+
 
 def test_mapping():
     with pytest.raises(ConversionError) as exc: