WIP

Author: Philipp Leger

changelog.d/324.change.rst

@@ -0,0 +1 @@
+``attr.s`` now auto-detects user-written methods and does not overwrite them. # is missing the __hash__ == None if it shouldn't be hashable

src/attr/_make.py

@@ -555,56 +555,74 @@ def slots_setstate(self, state):
         return cls
 
     def add_repr(self, ns):
-        self._cls_dict["__repr__"] = self._add_method_dunders(
-            _make_repr(self._attrs, ns=ns)
-        )
+        if "__repr__" in self._cls.__dict__:
+            meth = getattr(self._cls, "__repr__")
+        else:
+            meth = self._add_method_dunders(_make_repr(self._attrs, ns=ns))
+
+        self._cls_dict["__repr__"] = meth
         return self
 
     def add_str(self):
-        repr = self._cls_dict.get("__repr__")
-        if repr is None:
-            raise ValueError(
-                "__str__ can only be generated if a __repr__ exists."
-            )
+        if "__str__" in self._cls.__dict__:
+            meth = getattr(self._cls, "__str__")
+        else:
+            repr = self._cls_dict.get("__repr__")
+            if repr is None:
+                raise ValueError(
+                    "__str__ can only be generated if a __repr__ exists."
+                )
 
-        def __str__(self):
-            return self.__repr__()
+            def __str__(self):
+                return self.__repr__()
 
-        self._cls_dict["__str__"] = self._add_method_dunders(__str__)
+            meth = self._add_method_dunders(__str__)
+
+        self._cls_dict["__str__"] = meth
         return self
 
     def make_unhashable(self):
         self._cls_dict["__hash__"] = None
         return self
 
     def add_hash(self):
-        self._cls_dict["__hash__"] = self._add_method_dunders(
-            _make_hash(self._attrs)
-        )
+        if "__hash__" in self._cls.__dict__:
+            meth = getattr(self._cls, "__hash__")
+        else:
+            meth = self._add_method_dunders(_make_hash(self._attrs))
 
+        self._cls_dict["__hash__"] = meth
         return self
 
     def add_init(self):
-        self._cls_dict["__init__"] = self._add_method_dunders(
-            _make_init(
-                self._attrs,
-                self._has_post_init,
-                self._frozen,
-                self._slots,
-                self._super_attr_map,
+        if "__init__" in self._cls.__dict__:
+            meth = getattr(self._cls, "__init__")
+        else:
+            meth = self._add_method_dunders(
+                _make_init(
+                    self._attrs,
+                    self._has_post_init,
+                    self._frozen,
+                    self._slots,
+                    self._super_attr_map,
+                )
             )
-        )
 
+        self._cls_dict["__init__"] = meth
         return self
 
     def add_cmp(self):
         cd = self._cls_dict
 
-        cd["__eq__"], cd["__ne__"], cd["__lt__"], cd["__le__"], cd[
-            "__gt__"
-        ], cd["__ge__"] = (
-            self._add_method_dunders(meth) for meth in _make_cmp(self._attrs)
-        )
+        for meth in _make_cmp(self._attrs):
+            method_name = meth.__name__
+
+            if method_name in self._cls.__dict__:
+                meth = getattr(self._cls, method_name)
+            else:
+                meth = self._add_method_dunders(meth)
+
+            cd[method_name] = meth
 
         return self
 

tests/test_make.py

@@ -422,21 +422,21 @@ def test_adds_all_by_default(self, method_name):
         If no further arguments are supplied, all add_XXX functions except
         add_hash are applied.  __hash__ is set to None.
         """
-        # Set the method name to a sentinel and check whether it has been
-        # overwritten afterwards.
-        sentinel = object()
 
         class C(object):
             x = attr.ib()
 
-        setattr(C, method_name, sentinel)
+        # Assert that the method does not exist yet.
+        assert method_name not in C.__dict__
 
         C = attr.s(C)
-        meth = getattr(C, method_name)
 
-        assert sentinel != meth
+        method = getattr(C, method_name)
+
         if method_name == "__hash__":
-            assert meth is None
+            assert method is None
+        else:
+            assert method is not None
 
     @pytest.mark.parametrize(
         "arg_name, method_name",
@@ -1270,6 +1270,65 @@ class C2(C):
 
         assert [C2] == C.__subclasses__()
 
+    @pytest.mark.parametrize(
+        "method_name",
+        [
+            "__init__",
+            "__hash__",
+            "__repr__",
+            "__str__",
+            "__eq__",
+            "__ne__",
+            "__lt__",
+            "__le__",
+            "__gt__",
+            "__ge__",
+        ],
+    )
+    def test_respect_user_defined_methods(self, method_name):
+        """
+          Does not replace methods provided by the original class.
+        """
+
+        # Set the method name to a sentinel and check that it has not been
+        # overwritten afterwards.
+        def sentinel():
+            pass
+
+        # add_cmp relies on __name__.
+        sentinel.__name__ = method_name
+
+        class C(object):
+            x = attr.ib()
+
+        setattr(C, method_name, sentinel)
+
+        # set sentinel to unbound method of C otherwise assertion for py27
+        # doesn't work
+        sentinel = getattr(C, method_name)
+
+        C = attr.s(C, hash=True)
+
+        assert sentinel == getattr(C, method_name)
+
+    def test_ignores_user_defined_hash_method(self):
+        """
+          if it should be unhashable, the '__hash__' method is replaced.
+        """
+
+        # Set the method name to a sentinel and check that it has not been
+        # overwritten afterwards.
+        sentinel = object()
+
+        class C(object):
+            x = attr.ib()
+
+        setattr(C, "__hash__", sentinel)
+
+        C = attr.s(C)
+
+        assert getattr(C, "__hash__") is None
+
 
 class TestMakeCmp:
     """