Raise UnknownType exception with better error message.

Author: python-desert

CHANGELOG.rst

@@ -1,3 +1,14 @@
+2019.12.10
+--------------
+
+Changes
+^^^^^^^
+
+- Add ``UnknownType`` exception with better error message for types that should be generic.
+  `#8  <https://github.com/python-desert/desert/issues/8>`_
+
+
+
 2019.12.09
 --------------
 

src/desert/_make.py

@@ -106,6 +106,11 @@ def class_schema(clazz: type, meta: Dict[str, Any] = {}) -> Type[marshmallow.Sch
         fields = dataclasses.fields(clazz)
     elif attr.has(clazz):
         fields = attr.fields(clazz)
+    elif issubclass(clazz, (list, dict)):
+        raise desert.exceptions.UnknownType(
+            "Use parametrized generics like typing.List[int] or typing.Dict[str, int] "
+            f"instead of list and dict. Got {clazz}"
+        )
     else:
         raise desert.exceptions.NotAnAttrsClassOrDataclass(clazz)
 

src/desert/_version.py

@@ -1 +1 @@
-__version__ = "2019.12.09"
+__version__ = "2019.12.10"

src/desert/exceptions.py

@@ -9,3 +9,7 @@ class DesertException(Exception):
 
 class NotAnAttrsClassOrDataclass(DesertException):
     """Raised for dataclass operations on non-dataclasses."""
+
+
+class UnknownType(DesertException):
+    """Raised for a type with unknown serialization equivalent."""

tests/test_make.py

@@ -344,3 +344,14 @@ class A:
     schema = schema_class()
     data = schema.load({"x": 1, "y": 2})
     assert data == A(x=1)
+
+
+def test_raise_unknown_type(module):
+    """Raise UnknownType for failed inferences."""
+
+    @module.dataclass
+    class A:
+        x: list
+
+    with pytest.raises(desert.exceptions.UnknownType):
+        desert.schema_class(A)