bpo-42455: Add decorator_factory to functools module

Lib/functools.py

@@ -12,7 +12,7 @@
 __all__ = ['update_wrapper', 'wraps', 'WRAPPER_ASSIGNMENTS', 'WRAPPER_UPDATES',
            'total_ordering', 'cache', 'cmp_to_key', 'lru_cache', 'reduce',
            'partial', 'partialmethod', 'singledispatch', 'singledispatchmethod',
-           'cached_property']
+           'cached_property', 'decorator_factory']
 
 from abc import get_cache_token
 from collections import namedtuple
@@ -979,3 +979,19 @@ def __get__(self, instance, owner=None):
         return val
 
     __class_getitem__ = classmethod(GenericAlias)
+
+
+def decorator_factory(func):
+    """Transform function into decorator"""
+
+    @wraps(func)
+    def decorator(*args, **kwargs):
+        if args and callable(args[0]):
+            return func(*args, **kwargs)
+
+        def wrapper(f):
+            return func(f, *args, **kwargs)
+
+        return wrapper
+
+    return decorator

Lib/test/test_functools.py

@@ -2615,5 +2615,62 @@ def test_doc(self):
         self.assertEqual(CachedCostItem.cost.__doc__, "The cost of the item.")
 
 
+class TestDecoratorFactory(unittest.TestCase):
+    def test_wrapping_attributes(self):
+        @py_functools.decorator_factory
+        def function(func, /, a, b):
+            """This is function"""
+            return "Test"
+
+        self.assertEqual(function.__name__, "function")
+        if sys.flags.optimize < 2:
+            self.assertEqual(function.__doc__, "This is function")
+
+    def test_default_values(self):
+        @py_functools.decorator_factory
+        def decorator(func, /, a=1):
+            def wrapper(*args, **kwargs):
+                return a
+
+            return wrapper
+
+        @decorator
+        def a():
+            pass
+
+        @decorator()
+        def b():
+            pass
+
+        @decorator(a=2)
+        def c():
+            pass
+
+        self.assertEqual(a(), 1)
+        self.assertEqual(b(), 1)
+        self.assertEqual(c(), 2)
+
+    def test_params_without_default_value(self):
+        @py_functools.decorator_factory
+        def decorator(func, /, a):
+            return func
+
+        with self.assertRaises(TypeError):
+            @decorator
+            def a():
+                pass
+
+    def test_wraps_correct_function(self):
+        @py_functools.decorator_factory
+        def decorator(func, /):
+            return func
+
+        def a():
+            pass
+
+        self.assertIs(decorator(a), a)
+        self.assertIs(decorator()(a), a)
+
+
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Library/2020-11-24-22-36-09.bpo-42455.QhQV_V.rst

@@ -0,0 +1,2 @@
+Add ``decorator_factory`` function to ``functools`` module. Patch
+provided by Yurii Karabas.