bpo-40148: Add PurePath.with_stem() (GH-19295)

Add PurePath.with_stem()

2 files changed, 35 insertions, 0 deletions

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 88ebe03..f98d69e 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -870,6 +870,10 @@ class PurePath(object):
         return self._from_parsed_parts(self._drv, self._root,
                                        self._parts[:-1] + [name])
 
+    def with_stem(self, stem):
+        """Return a new path with the stem changed."""
+        return self.with_name(stem + self.suffix)
+
     def with_suffix(self, suffix):
         """Return a new path with the file suffix changed.  If the path
         has no suffix, add given suffix.  If the given suffix is an empty
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 8b19cff..1589282 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -559,6 +559,23 @@ class _BasePurePathTest(object):
         self.assertRaises(ValueError, P('a/b').with_name, 'c/')
         self.assertRaises(ValueError, P('a/b').with_name, 'c/d')
 
+    def test_with_stem_common(self):
+        P = self.cls
+        self.assertEqual(P('a/b').with_stem('d'), P('a/d'))
+        self.assertEqual(P('/a/b').with_stem('d'), P('/a/d'))
+        self.assertEqual(P('a/b.py').with_stem('d'), P('a/d.py'))
+        self.assertEqual(P('/a/b.py').with_stem('d'), P('/a/d.py'))
+        self.assertEqual(P('/a/b.tar.gz').with_stem('d'), P('/a/d.gz'))
+        self.assertEqual(P('a/Dot ending.').with_stem('d'), P('a/d'))
+        self.assertEqual(P('/a/Dot ending.').with_stem('d'), P('/a/d'))
+        self.assertRaises(ValueError, P('').with_stem, 'd')
+        self.assertRaises(ValueError, P('.').with_stem, 'd')
+        self.assertRaises(ValueError, P('/').with_stem, 'd')
+        self.assertRaises(ValueError, P('a/b').with_stem, '')
+        self.assertRaises(ValueError, P('a/b').with_stem, '/c')
+        self.assertRaises(ValueError, P('a/b').with_stem, 'c/')
+        self.assertRaises(ValueError, P('a/b').with_stem, 'c/d')
+
     def test_with_suffix_common(self):
         P = self.cls
         self.assertEqual(P('a/b').with_suffix('.gz'), P('a/b.gz'))
@@ -1014,6 +1031,20 @@ class PureWindowsPathTest(_BasePurePathTest, unittest.TestCase):
         self.assertRaises(ValueError, P('c:a/b').with_name, 'd:/e')
         self.assertRaises(ValueError, P('c:a/b').with_name, '//My/Share')
 
+    def test_with_stem(self):
+        P = self.cls
+        self.assertEqual(P('c:a/b').with_stem('d'), P('c:a/d'))
+        self.assertEqual(P('c:/a/b').with_stem('d'), P('c:/a/d'))
+        self.assertEqual(P('c:a/Dot ending.').with_stem('d'), P('c:a/d'))
+        self.assertEqual(P('c:/a/Dot ending.').with_stem('d'), P('c:/a/d'))
+        self.assertRaises(ValueError, P('c:').with_stem, 'd')
+        self.assertRaises(ValueError, P('c:/').with_stem, 'd')
+        self.assertRaises(ValueError, P('//My/Share').with_stem, 'd')
+        self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:')
+        self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:e')
+        self.assertRaises(ValueError, P('c:a/b').with_stem, 'd:/e')
+        self.assertRaises(ValueError, P('c:a/b').with_stem, '//My/Share')
+
     def test_with_suffix(self):
         P = self.cls
         self.assertEqual(P('c:a/b').with_suffix('.gz'), P('c:a/b.gz'))