bpo-33129: Add kwarg support for dataclass' generated init method

Lib/dataclasses.py

@@ -526,7 +526,7 @@ def _init_fn(fields, frozen, has_post_init, self_name, globals):
         body_lines = ['pass']
 
     return _create_fn('__init__',
-                      [self_name] + [_init_param(f) for f in fields if f.init],
+                      [self_name] + [_init_param(f) for f in fields if f.init] + ['**kwargs'],
                       body_lines,
                       locals=locals,
                       globals=globals,

Lib/test/test_dataclasses.py

@@ -794,6 +794,8 @@ def validate_class(cls):
             self.assertIs   (param.annotation, float)
             # Don't test for the default, since it's set to MISSING.
             self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
+            param = next(params)
+            self.assertEqual(param.name, 'kwargs')
             self.assertRaises(StopIteration, next, params)
 
 
@@ -1990,22 +1992,22 @@ def test_docstring_no_fields(self):
         class C:
             pass
 
-        self.assertDocStrEqual(C.__doc__, "C()")
+        self.assertDocStrEqual(C.__doc__, "C(**kwargs)")
 
     def test_docstring_one_field(self):
         @dataclass
         class C:
             x: int
 
-        self.assertDocStrEqual(C.__doc__, "C(x:int)")
+        self.assertDocStrEqual(C.__doc__, "C(x:int, **kwargs)")
 
     def test_docstring_two_fields(self):
         @dataclass
         class C:
             x: int
             y: int
 
-        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int)")
+        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int, **kwargs)")
 
     def test_docstring_three_fields(self):
         @dataclass
@@ -2014,49 +2016,49 @@ class C:
             y: int
             z: str
 
-        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int, z:str)")
+        self.assertDocStrEqual(C.__doc__, "C(x:int, y:int, z:str, **kwargs)")
 
     def test_docstring_one_field_with_default(self):
         @dataclass
         class C:
             x: int = 3
 
-        self.assertDocStrEqual(C.__doc__, "C(x:int=3)")
+        self.assertDocStrEqual(C.__doc__, "C(x:int=3, **kwargs)")
 
     def test_docstring_one_field_with_default_none(self):
         @dataclass
         class C:
             x: Union[int, type(None)] = None
 
-        self.assertDocStrEqual(C.__doc__, "C(x:Union[int, NoneType]=None)")
+        self.assertDocStrEqual(C.__doc__, "C(x:Union[int, NoneType]=None, **kwargs)")
 
     def test_docstring_list_field(self):
         @dataclass
         class C:
             x: List[int]
 
-        self.assertDocStrEqual(C.__doc__, "C(x:List[int])")
+        self.assertDocStrEqual(C.__doc__, "C(x:List[int], **kwargs)")
 
     def test_docstring_list_field_with_default_factory(self):
         @dataclass
         class C:
             x: List[int] = field(default_factory=list)
 
-        self.assertDocStrEqual(C.__doc__, "C(x:List[int]=<factory>)")
+        self.assertDocStrEqual(C.__doc__, "C(x:List[int]=<factory>, **kwargs)")
 
     def test_docstring_deque_field(self):
         @dataclass
         class C:
             x: deque
 
-        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque)")
+        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque, **kwargs)")
 
     def test_docstring_deque_field_with_default_factory(self):
         @dataclass
         class C:
             x: deque = field(default_factory=deque)
 
-        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque=<factory>)")
+        self.assertDocStrEqual(C.__doc__, "C(x:collections.deque=<factory>, **kwargs)")
 
 
 class TestInit(unittest.TestCase):
@@ -3162,9 +3164,9 @@ class C:
         #  if we're also replacing one that does exist.  Test this
         #  here, because setting attributes on frozen instances is
         #  handled slightly differently from non-frozen ones.
-        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an unexpected "
-                                             "keyword argument 'a'"):
+        with self.assertRaisesRegex(AttributeError, r"'C' object has no attribute 'a'"):
             c1 = replace(c, x=20, a=5)
+            result = c1.a
 
     def test_invalid_field_name(self):
         @dataclass(frozen=True)
@@ -3173,9 +3175,9 @@ class C:
             y: int
 
         c = C(1, 2)
-        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an unexpected "
-                                    "keyword argument 'z'"):
+        with self.assertRaisesRegex(AttributeError, r"'C' object has no attribute 'z'"):
             c1 = replace(c, z=3)
+            result = c1.z
 
     def test_invalid_object(self):
         @dataclass(frozen=True)
@@ -3222,9 +3224,8 @@ class C:
         self.assertEqual(c.y, 1000)
 
         # Trying to replace y is an error: can't replace ClassVars.
-        with self.assertRaisesRegex(TypeError, r"__init__\(\) got an "
-                                    "unexpected keyword argument 'y'"):
-            replace(c, y=30)
+        c1 = replace(c, y=30)
+        self.assertEqual(c, c1)
 
         replace(c, x=5)
 

Misc/NEWS.d/next/Core and Builtins/2020-03-28-20-10-52.bpo-33129.owLqbD.rst

@@ -0,0 +1 @@
+Added kwargs support for dataclass' generated init method so that we can more expressively interact with HTTP response body objects by extracting the object members we want and ignoring the rest without raising an TypeError exception.