Respecting defaults from attr class

cattr/converters.py

@@ -283,10 +283,10 @@ def _structure_attr_from_dict(self, a, name, mapping):
         type_ = a.metadata.get(TYPE_METADATA_KEY)
         if type_ is None:
             # No type.
-            return mapping[name]
+            return mapping.get(name, a.default)
         if _is_union_type(type_):
             # This is a union.
-            val = mapping.get(name, NOTHING)
+            val = mapping.get(name, a.default)
             if NoneType in type_.__args__ and val is NOTHING:
                 return None
             return self._structure_union(val, type_)

tests/test_structure_attrs.py

@@ -1,10 +1,10 @@
 """Loading of attrs classes."""
-from attr import asdict, astuple, fields
+from attr import asdict, astuple, fields, make_class
 from hypothesis import assume, given
 
 from typing import Union
 
-from . import simple_classes
+from . import simple_classes, simple_attrs
 
 
 @given(simple_classes())
@@ -20,6 +20,16 @@ def test_structure_simple_from_dict(converter, cl_and_vals):
     assert obj == loaded
 
 
+@given(simple_attrs(defaults=True))
+def test_structure_simple_from_dict_default(converter, cl_and_vals):
+    """Test structuring non-nested attrs classes with default value."""
+    a, _ = cl_and_vals
+    cl = make_class("HypClass", {"a": a})
+    obj = cl()
+    loaded = converter.structure({}, cl)
+    assert obj == loaded
+
+
 @given(simple_classes())
 def test_roundtrip(converter, cl_and_vals):
     # type: (Converter, Any) -> None