Fix default values that are not comparable with '==' (#586)

Fix #585

changelog.d/585.change.rst

@@ -0,0 +1 @@
+Fixed ``auto_attribs`` usage when default values cannot be compared directly with ``==``, such as ``numpy`` arrays.

src/attr/_make.py

@@ -509,7 +509,7 @@ def _patch_original_class(self):
             for name in self._attr_names:
                 if (
                     name not in base_names
-                    and getattr(cls, name, _sentinel) != _sentinel
+                    and getattr(cls, name, _sentinel) is not _sentinel
                 ):
                     try:
                         delattr(cls, name)

tests/test_annotations.py

@@ -282,3 +282,18 @@ class C:
 
         with pytest.raises(AttributeError):
             C.y
+
+    def test_non_comparable_defaults(self):
+        """
+        Regression test for #585: objects that are not directly comparable
+        (for example numpy arrays) would cause a crash when used as
+        default values of an attrs auto-attrib class.
+        """
+
+        class NonComparable:
+            def __eq__(self, other):
+                raise ValueError
+
+        @attr.s(auto_attribs=True)
+        class C:
+            x: typing.Any = NonComparable()