bpo-32380: Create functools.singledispatchmethod (#6306)

Lib/test/test_functools.py

@@ -2147,6 +2147,124 @@ class TestSingleDispatch(unittest.TestCase):
                 return self.arg == other
         self.assertEqual(i("str"), "str")
 
+    def test_method_register(self):
+        class A:
+            @functools.singledispatchmethod
+            def t(self, arg):
+                self.arg = "base"
+            @t.register(int)
+            def _(self, arg):
+                self.arg = "int"
+            @t.register(str)
+            def _(self, arg):
+                self.arg = "str"
+        a = A()
+
+        a.t(0)
+        self.assertEqual(a.arg, "int")
+        aa = A()
+        self.assertFalse(hasattr(aa, 'arg'))
+        a.t('')
+        self.assertEqual(a.arg, "str")
+        aa = A()
+        self.assertFalse(hasattr(aa, 'arg'))
+        a.t(0.0)
+        self.assertEqual(a.arg, "base")
+        aa = A()
+        self.assertFalse(hasattr(aa, 'arg'))
+
+    def test_staticmethod_register(self):
+        class A:
+            @functools.singledispatchmethod
+            @staticmethod
+            def t(arg):
+                return arg
+            @t.register(int)
+            @staticmethod
+            def _(arg):
+                return isinstance(arg, int)
+            @t.register(str)
+            @staticmethod
+            def _(arg):
+                return isinstance(arg, str)
+        a = A()
+
+        self.assertTrue(A.t(0))
+        self.assertTrue(A.t(''))
+        self.assertEqual(A.t(0.0), 0.0)
+
+    def test_classmethod_register(self):
+        class A:
+            def __init__(self, arg):
+                self.arg = arg
+
+            @functools.singledispatchmethod
+            @classmethod
+            def t(cls, arg):
+                return cls("base")
+            @t.register(int)
+            @classmethod
+            def _(cls, arg):
+                return cls("int")
+            @t.register(str)
+            @classmethod
+            def _(cls, arg):
+                return cls("str")
+
+        self.assertEqual(A.t(0).arg, "int")
+        self.assertEqual(A.t('').arg, "str")
+        self.assertEqual(A.t(0.0).arg, "base")
+
+    def test_callable_register(self):
+        class A:
+            def __init__(self, arg):
+                self.arg = arg
+
+            @functools.singledispatchmethod
+            @classmethod
+            def t(cls, arg):
+                return cls("base")
+
+        @A.t.register(int)
+        @classmethod
+        def _(cls, arg):
+            return cls("int")
+        @A.t.register(str)
+        @classmethod
+        def _(cls, arg):
+            return cls("str")
+
+        self.assertEqual(A.t(0).arg, "int")
+        self.assertEqual(A.t('').arg, "str")
+        self.assertEqual(A.t(0.0).arg, "base")
+
+    def test_abstractmethod_register(self):
+        class Abstract(abc.ABCMeta):
+
+            @functools.singledispatchmethod
+            @abc.abstractmethod
+            def add(self, x, y):
+                pass
+
+        self.assertTrue(Abstract.add.__isabstractmethod__)
+
+    def test_type_ann_register(self):
+        class A:
+            @functools.singledispatchmethod
+            def t(self, arg):
+                return "base"
+            @t.register
+            def _(self, arg: int):
+                return "int"
+            @t.register
+            def _(self, arg: str):
+                return "str"
+        a = A()
+
+        self.assertEqual(a.t(0), "int")
+        self.assertEqual(a.t(''), "str")
+        self.assertEqual(a.t(0.0), "base")
+
     def test_invalid_registrations(self):
         msg_prefix = "Invalid first argument to `register()`: "
         msg_suffix = (