Minor fixes to dataclass tests. (GH-6243)

 Also, re-enable a test for ClassVars with default_factory.

Lib/test/test_dataclasses.py

@@ -133,8 +133,8 @@ class TestCase(unittest.TestCase):
         self.assertEqual(hash(C(10)), hash((10,)))
 
         # Creating this class should generate an exception, because
-        # __hash__ exists and is not None, which it would be if it had
-        # been auto-generated do due __eq__ being defined.
+        #  __hash__ exists and is not None, which it would be if it
+        #  had been auto-generated due to __eq__ being defined.
         with self.assertRaisesRegex(TypeError,
                                     'Cannot overwrite attribute __hash__'):
             @dataclass(unsafe_hash=True)
@@ -145,7 +145,6 @@ class TestCase(unittest.TestCase):
                 def __hash__(self):
                     pass
 
-
     def test_overwrite_fields_in_derived_class(self):
         # Note that x from C1 replaces x in Base, but the order remains
         #  the same as defined in Base.
@@ -624,7 +623,7 @@ class TestCase(unittest.TestCase):
         self.assertIs(o1.x, o2.x)
 
     def test_no_options(self):
-        # call with dataclass()
+        # Call with dataclass().
         @dataclass()
         class C:
             x: int
@@ -639,7 +638,7 @@ class TestCase(unittest.TestCase):
             y: int
         self.assertNotEqual(Point(1, 2), (1, 2))
 
-        # And that we can't compare to another unrelated dataclass
+        # And that we can't compare to another unrelated dataclass.
         @dataclass
         class C:
             x: int
@@ -664,7 +663,7 @@ class TestCase(unittest.TestCase):
         self.assertNotEqual(Point3D(2017, 6, 3), Date(2017, 6, 3))
         self.assertNotEqual(Point3D(1, 2, 3), (1, 2, 3))
 
-        # Make sure we can't unpack
+        # Make sure we can't unpack.
         with self.assertRaisesRegex(TypeError, 'unpack'):
             x, y, z = Point3D(4, 5, 6)
 
@@ -695,7 +694,7 @@ class TestCase(unittest.TestCase):
             # Verify __init__.
 
             signature = inspect.signature(cls.__init__)
-            # Check the return type, should be None
+            # Check the return type, should be None.
             self.assertIs(signature.return_annotation, None)
 
             # Check each parameter.
@@ -716,12 +715,12 @@ class TestCase(unittest.TestCase):
             param = next(params)
             self.assertEqual(param.name, 'k')
             self.assertIs   (param.annotation, F)
-            # Don't test for the default, since it's set to MISSING
+            # 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, 'l')
             self.assertIs   (param.annotation, float)
-            # Don't test for the default, since it's set to MISSING
+            # Don't test for the default, since it's set to MISSING.
             self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD)
             self.assertRaises(StopIteration, next, params)
 
@@ -867,7 +866,7 @@ class TestCase(unittest.TestCase):
 
         self.assertEqual(C().x, 5)
 
-        # Now call super(), and it will raise
+        # Now call super(), and it will raise.
         @dataclass
         class C(B):
             def __post_init__(self):
@@ -928,8 +927,8 @@ class TestCase(unittest.TestCase):
 
         c = C(5)
         self.assertEqual(repr(c), 'TestCase.test_class_var.<locals>.C(x=5, y=10)')
-        self.assertEqual(len(fields(C)), 2)                 # We have 2 fields
-        self.assertEqual(len(C.__annotations__), 5)         # And 3 ClassVars
+        self.assertEqual(len(fields(C)), 2)                 # We have 2 fields.
+        self.assertEqual(len(C.__annotations__), 5)         # And 3 ClassVars.
         self.assertEqual(c.z, 1000)
         self.assertEqual(c.w, 2000)
         self.assertEqual(c.t, 3000)
@@ -1205,15 +1204,14 @@ class TestCase(unittest.TestCase):
         d = D(4, 5)
         self.assertEqual((d.x, d.z), (4, 5))
 
-
-    def x_test_classvar_default_factory(self):
-        # XXX: it's an error for a ClassVar to have a factory function
+    def test_classvar_default_factory(self):
+        # It's an error for a ClassVar to have a factory function.
+        with self.assertRaisesRegex(TypeError,
+                                    'cannot have a default factory'):
             @dataclass
             class C:
                 x: ClassVar[int] = field(default_factory=int)
 
-        self.assertIs(C().x, int)
-
     def test_is_dataclass(self):
         class NotDataClass:
             pass
@@ -1264,7 +1262,7 @@ class TestCase(unittest.TestCase):
             fields(C())
 
     def test_helper_asdict(self):
-        # Basic tests for asdict(), it should return a new dictionary
+        # Basic tests for asdict(), it should return a new dictionary.
         @dataclass
         class C:
             x: int
@@ -1279,7 +1277,7 @@ class TestCase(unittest.TestCase):
         self.assertIs(type(asdict(c)), dict)
 
     def test_helper_asdict_raises_on_classes(self):
-        # asdict() should raise on a class object
+        # asdict() should raise on a class object.
         @dataclass
         class C:
             x: int
@@ -1377,7 +1375,7 @@ class TestCase(unittest.TestCase):
         self.assertIs(type(d), OrderedDict)
 
     def test_helper_astuple(self):
-        # Basic tests for astuple(), it should return a new tuple
+        # Basic tests for astuple(), it should return a new tuple.
         @dataclass
         class C:
             x: int
@@ -1392,7 +1390,7 @@ class TestCase(unittest.TestCase):
         self.assertIs(type(astuple(c)), tuple)
 
     def test_helper_astuple_raises_on_classes(self):
-        # astuple() should raise on a class object
+        # astuple() should raise on a class object.
         @dataclass
         class C:
             x: int
@@ -1489,7 +1487,7 @@ class TestCase(unittest.TestCase):
         self.assertIs(type(t), NT)
 
     def test_dynamic_class_creation(self):
-        cls_dict = {'__annotations__': {'x':int, 'y':int},
+        cls_dict = {'__annotations__': {'x': int, 'y': int},
                     }
 
         # Create the class.
@@ -1502,7 +1500,7 @@ class TestCase(unittest.TestCase):
         self.assertEqual(asdict(cls(1, 2)), {'x': 1, 'y': 2})
 
     def test_dynamic_class_creation_using_field(self):
-        cls_dict = {'__annotations__': {'x':int, 'y':int},
+        cls_dict = {'__annotations__': {'x': int, 'y': int},
                     'y': field(default=5),
                     }
 
@@ -1569,8 +1567,8 @@ class TestCase(unittest.TestCase):
 
     def test_alternate_classmethod_constructor(self):
         # Since __post_init__ can't take params, use a classmethod
-        # alternate constructor. This is mostly an example to show how
-        # to use this technique.
+        #  alternate constructor.  This is mostly an example to show
+        #  how to use this technique.
         @dataclass
         class C:
             x: int
@@ -1604,7 +1602,7 @@ class TestCase(unittest.TestCase):
             class C:
                 i: int = field(metadata=0)
 
-        # Make sure an empty dict works
+        # Make sure an empty dict works.
         @dataclass
         class C:
             i: int = field(metadata={})
@@ -1666,7 +1664,7 @@ class TestCase(unittest.TestCase):
         self.assertEqual(box.content, 42)
         self.assertEqual(box.label, '<unknown>')
 
-        # subscripting the resulting class should work, etc.
+        # Subscripting the resulting class should work, etc.
         Alias = List[LabeledBox[int]]
 
     def test_generic_extending(self):
@@ -2178,7 +2176,7 @@ class TestRepr(unittest.TestCase):
 
 class TestFrozen(unittest.TestCase):
     def test_overwriting_frozen(self):
-        # frozen uses __setattr__ and __delattr__
+        # frozen uses __setattr__ and __delattr__.
         with self.assertRaisesRegex(TypeError,
                                     'Cannot overwrite attribute __setattr__'):
             @dataclass(frozen=True)
@@ -2535,8 +2533,8 @@ class TestHash(unittest.TestCase):
                 elif expected == 'object':
                     # I'm not sure what test to use here.  object's
                     #  hash isn't based on id(), so calling hash()
-                    # won't tell us much.  So, just check the function
-                    # used is object's.
+                    #  won't tell us much.  So, just check the
+                    #  function used is object's.
                     self.assertIs(C.__hash__, object.__hash__)
 
                 elif expected == 'tuple':
@@ -2665,8 +2663,9 @@ class TestSlots(unittest.TestCase):
             __slots__ = ('x',)
             x: Any
 
-        # There was a bug where a variable in a slot was assumed
-        #  to also have a default value (of type types.MemberDescriptorType).
+        # There was a bug where a variable in a slot was assumed to
+        #  also have a default value (of type
+        #  types.MemberDescriptorType).
         with self.assertRaisesRegex(TypeError,
                                     r"__init__\(\) missing 1 required positional argument: 'x'"):
             C()