in 3.6 types can have __args__ = None, as opposed to missing attribute

Author: jaymccon

src/cloudformation_cli_python_lib/recast.py

@@ -90,12 +90,14 @@ def _field_to_type(field: Any, key: str, classes: Dict[str, Any]) -> Any:
     # Assuming this is a generic object created by typing.Union
     try:
         possible_types = field.__args__
+        if not possible_types:
+            raise InvalidRequest(f"Cannot process type {field} for field {key}")
     except AttributeError:
         raise InvalidRequest(f"Cannot process type {field} for field {key}")
     # Assuming that the union is generated from typing.Optional, so only
     # contains one type and None
     # pylint: disable=unidiomatic-typecheck
-    fields = [t for t in possible_types if type(None) != t] if possible_types else []
+    fields = [t for t in possible_types if type(None) != t]
     if len(fields) != 1:
         raise InvalidRequest(f"Cannot process type {field} for field {key}")
     field = fields[0]

tests/lib/recast_test.py

@@ -121,6 +121,28 @@ def test_field_to_type_unhandled_types():
         assert str(excinfo.value).startswith("Cannot process type ")
 
 
+def test_field_to_type_unhandled_types_36():
+    k = "key"
+
+    class SixType:
+        __args__ = None
+
+    with pytest.raises(InvalidRequest) as excinfo:
+        _field_to_type(SixType, k, {})
+    assert str(excinfo.value).startswith("Cannot process type ")
+
+
+def test_field_to_type_unhandled_types_37():
+    k = "key"
+
+    class SevenType:
+        pass
+
+    with pytest.raises(InvalidRequest) as excinfo:
+        _field_to_type(SevenType, k, {})
+    assert str(excinfo.value).startswith("Cannot process type ")
+
+
 def test_get_forward_ref_type():
     with patch("cloudformation_cli_python_lib.recast.typing") as mock_typing:
         mock_typing.ForwardRef = "3.7+"