Call into BaseException to initialiaze self.args

src/attr/_make.py

@@ -1666,18 +1666,12 @@ def fmt_setter_with_converter(attr_name, value_var):
             init_hash_cache = "self.%s = %s"
         lines.append(init_hash_cache % (_hash_cache_field, "None"))
 
-    # On Python 2, it's necessary to set self.args for exceptions. We do it on
-    # *all* versions to keep around defaults.
+    # For exceptions we rely on BaseException.__init__ for proper
+    # initialization.
     if is_exc:
-        vals = "".join(("(self.", ", self.".join(a.name for a in attrs), ",)"))
+        vals = ",".join("self." + a.name for a in attrs if a.init)
 
-        if frozen:
-            if slots:
-                lines.append("_setattr('args', %s)" % (vals,))
-            else:
-                lines.append("object.__setattr__(self, 'args', %s)" % (vals,))
-        else:
-            lines.append("self.args = " + vals)
+        lines.append("BaseException.__init__(self, %s)" % (vals,))
 
     args = ", ".join(args)
     if kw_only_args:

tests/test_dark_magic.py

@@ -6,6 +6,8 @@
 
 import pickle
 
+from copy import deepcopy
+
 import pytest
 import six
 
@@ -550,13 +552,15 @@ class FooError(Exception):
 
             assert e is e
             assert e == e
-            assert "(1, 42, 'foo')" == str(e)
-            # N.B. the default value 42 is preserved by setting args ourselves.
-            assert (1, 42, "foo") == e.args
+            assert "(1, 'foo')" == str(e)
+            assert (1, "foo") == e.args
 
             with pytest.raises(TypeError):
                 hash(e)
 
+            if not frozen:
+                deepcopy(e)
+
     @pytest.mark.parametrize("slots", [True, False])
     @pytest.mark.parametrize("frozen", [True, False])
     def test_auto_exc_one_attrib(self, slots, frozen):