Change __getattribute__ to raise AttributeErrors instead of KeyErrors

src/implicitdict/__init__.py

@@ -152,7 +152,10 @@ def __getattribute__(self, item):
             self_type_name = _fullname(self_type)
             if self_type_name in fields_info_by_type:
                 if item in fields_info_by_type[self_type_name].all_fields:
-                    return self[item]
+                    try:
+                        return self[item]
+                    except KeyError:
+                        raise AttributeError
         return super(ImplicitDict, self).__getattribute__(item)
 
     def __setattr__(self, key, value):
@@ -165,7 +168,7 @@ def __setattr__(self, key, value):
                     self[key] = value
                     return
                 else:
-                    raise KeyError('Attribute "{}" is not defined for "{}" object'.format(key, type(self).__name__))
+                    raise AttributeError('Attribute "{}" is not defined for "{}" object'.format(key, type(self).__name__))
         super(ImplicitDict, self).__setattr__(key, value)
 
     def has_field_with_value(self, field_name: str) -> bool:

tests/test_normal_usage.py

@@ -23,7 +23,7 @@ def test_basic_usage():
 
     # Optional fields that aren't specified simply don't exist
     assert 'baz' not in data
-    with pytest.raises(KeyError):
+    with pytest.raises(AttributeError):
         assert data.baz == 0
 
     # Optional fields can be omitted (fields with defaults are optional)

tests/test_optional.py

@@ -42,8 +42,8 @@ def test_minimally_defined():
     assert "field_with_default" in data
     assert "optional_field2_with_none_default" in data
     assert "optional_field3_with_default" in data
-    with pytest.raises(KeyError):
-        # Trying to reference the Optional field will result in a KeyError
+    with pytest.raises(AttributeError):
+        # Trying to reference the Optional field will result in a AttributeError
         # To determine whether an Optional field is present, the user must check
         # whether `"<FIELD_NAME>" in <OBJECT>` (see above).
         assert data.optional_field1 == None