gh-74033: Fix bug when Path takes and ignores **kwargs

Lib/pathlib.py

@@ -390,7 +390,7 @@ class PurePath(object):
         '_str', '_hash', '_pparts', '_cached_cparts',
     )
 
-    def __new__(cls, *args):
+    def __new__(cls, *args, **kwargs):
         """Construct a PurePath from one or several strings and or existing
         PurePath objects.  The strings and path objects are combined so as
         to yield a canonicalized path, which is incorporated into the
@@ -400,6 +400,9 @@ def __new__(cls, *args):
             cls = PureWindowsPath if os.name == 'nt' else PurePosixPath
         return cls._from_parts(args)
 
+    def __init__(self, *_):
+        pass  # bpo-29847
+
     def __reduce__(self):
         # Using the parts tuple helps share interned path parts
         # when pickling related paths.

Lib/test/test_pathlib.py

@@ -739,6 +739,22 @@ def test_pickling_common(self):
             self.assertEqual(hash(pp), hash(p))
             self.assertEqual(str(pp), str(p))
 
+    def test_kwargs(self):
+        with self.assertRaisesRegex(TypeError, 'got an unexpected keyword argument'):
+            self.cls(arg=None)
+
+    def test_subclass_kwargs(self):
+        # See bpo-29847
+        class _PathSubclass(self.cls):
+            _flavour = self.cls()._flavour
+
+            def __init__(self, *args, **kwargs):
+                self.kwargs = kwargs
+
+        _kwargs = {"a": 1, "b": 2}
+        p = _PathSubclass(**_kwargs)
+        self.assertEqual(p.kwargs, _kwargs)
+
 
 class PurePosixPathTest(_BasePurePathTest, unittest.TestCase):
     cls = pathlib.PurePosixPath

Misc/NEWS.d/next/Library/2020-04-18-17-45-03.bpo-29847.Uxtbq0.rst

@@ -0,0 +1 @@
+Fix bug where :class:`pathlib.PurePath` and its subclasses take and ignore `**kwargs`. Patch provided by Yurii Karabas.