Fix __repr__ crashing when a member is uninitialized or deleted

changelog.d/308.breaking.rst

@@ -0,0 +1,20 @@
+The ``__repr__`` set by ``attrs``
+no longer produces an ``AttributeError``
+when the instance is missing some of the specified attributes
+(either through deleting
+or after using ``init=False`` on some attributes).
+
+This can break code
+that relied on ``repr(attr_cls_instance)`` raising ``AttributeError``
+to check if any attr-specified members were unset.
+
+If you were using this,
+you can implement a custom method for checking this::
+
+    def has_unset_members(self):
+        for field in attr.fields(type(self)):
+            try:
+                getattr(self, field.name)
+            except AttributeError:
+                return True
+        return False

src/attr/_make.py

@@ -849,7 +849,7 @@ def repr_(self):
         return "{0}({1})".format(
             class_name,
             ", ".join(
-                name + "=" + repr(getattr(self, name))
+                name + "=" + repr(getattr(self, name, NOTHING))
                 for name in attr_names
             )
         )

tests/test_dunders.py

@@ -200,6 +200,16 @@ class C(object):
 
         assert "C(_x=42)" == repr(i)
 
+    def test_repr_uninitialized_member(self):
+        """
+        repr signals unset attributes
+        """
+        C = make_class("C", {
+            "a": attr.ib(init=False),
+        })
+
+        assert "C(a=NOTHING)" == repr(C())
+
     @given(add_str=booleans(), slots=booleans())
     def test_str(self, add_str, slots):
         """