GH-73991: Add pathlib.Path.copy_into() and move_into() (#123314)

These two methods accept an *existing* directory path, onto which we join
the source path's base name to form the final target path.

A possible alternative implementation is to check for directories in
`copy()` and `move()` and adjust the target path, which is done in several
`shutil` functions. This behaviour is helpful in a shell context, but
less so in a stored program that explicitly specifies destinations. For
example, a user that calls `Path('foo.py').copy('bar.py')` might not
imagine that `bar.py/foo.py` would be created, but under the alternative
implementation this will happen if `bar.py` is an existing directory.

Doc/library/pathlib.rst

@@ -1575,6 +1575,18 @@ Copying, moving and deleting
    .. versionadded:: 3.14
 
 
+.. method:: Path.copy_into(target_dir, *, follow_symlinks=True, \
+                           dirs_exist_ok=False, preserve_metadata=False, \
+                           ignore=None, on_error=None)
+
+   Copy this file or directory tree into the given *target_dir*, which should
+   be an existing directory. Other arguments are handled identically to
+   :meth:`Path.copy`. Returns a new :class:`!Path` instance pointing to the
+   copy.
+
+   .. versionadded:: 3.14
+
+
 .. method:: Path.rename(target)
 
    Rename this file or directory to the given *target*, and return a new
@@ -1633,6 +1645,15 @@ Copying, moving and deleting
    .. versionadded:: 3.14
 
 
+.. method:: Path.move_into(target_dir)
+
+   Move this file or directory tree into the given *target_dir*, which should
+   be an existing directory. Returns a new :class:`!Path` instance pointing to
+   the moved path.
+
+   .. versionadded:: 3.14
+
+
 .. method:: Path.unlink(missing_ok=False)
 
    Remove this file or symbolic link.  If the path points to a directory,

Doc/whatsnew/3.14.rst

@@ -188,10 +188,10 @@ pathlib
 * Add methods to :class:`pathlib.Path` to recursively copy, move, or remove
   files and directories:
 
-  * :meth:`~pathlib.Path.copy` copies a file or directory tree to a given
+  * :meth:`~pathlib.Path.copy` copies a file or directory tree to a destination.
-    destination.
+  * :meth:`~pathlib.Path.copy_into` copies *into* a destination directory.
-  * :meth:`~pathlib.Path.move` moves a file or directory tree to a given
+  * :meth:`~pathlib.Path.move` moves a file or directory tree to a destination.
-    destination.
+  * :meth:`~pathlib.Path.move_into` moves *into* a destination directory.
   * :meth:`~pathlib.Path.delete` removes a file or directory tree.
 
   (Contributed by Barney Gale in :gh:`73991`.)

Lib/pathlib/_abc.py

@@ -904,6 +904,24 @@ def copy(self, target, *, follow_symlinks=True, dirs_exist_ok=False,
                 on_error(err)
         return target
 
+    def copy_into(self, target_dir, *, follow_symlinks=True,
+                  dirs_exist_ok=False, preserve_metadata=False, ignore=None,
+                  on_error=None):
+        """
+        Copy this file or directory tree into the given existing directory.
+        """
+        name = self.name
+        if not name:
+            raise ValueError(f"{self!r} has an empty name")
+        elif isinstance(target_dir, PathBase):
+            target = target_dir / name
+        else:
+            target = self.with_segments(target_dir, name)
+        return self.copy(target, follow_symlinks=follow_symlinks,
+                         dirs_exist_ok=dirs_exist_ok,
+                         preserve_metadata=preserve_metadata, ignore=ignore,
+                         on_error=on_error)
+
     def rename(self, target):
         """
         Rename this path to the target path.
@@ -947,6 +965,19 @@ def move(self, target):
         self.delete()
         return target
 
+    def move_into(self, target_dir):
+        """
+        Move this file or directory tree into the given existing directory.
+        """
+        name = self.name
+        if not name:
+            raise ValueError(f"{self!r} has an empty name")
+        elif isinstance(target_dir, PathBase):
+            target = target_dir / name
+        else:
+            target = self.with_segments(target_dir, name)
+        return self.move(target)
+
     def chmod(self, mode, *, follow_symlinks=True):
         """
         Change the permissions of the path, like os.chmod().

Lib/test/test_pathlib/test_pathlib.py

@@ -861,6 +861,14 @@ def test_move_dir_symlink_to_itself_other_fs(self):
     def test_move_dangling_symlink_other_fs(self):
         self.test_move_dangling_symlink()
 
+    @patch_replace
+    def test_move_into_other_os(self):
+        self.test_move_into()
+
+    @patch_replace
+    def test_move_into_empty_name_other_os(self):
+        self.test_move_into_empty_name()
+
     def test_resolve_nonexist_relative_issue38671(self):
         p = self.cls('non', 'exist')
 

Lib/test/test_pathlib/test_pathlib_abc.py

@@ -2072,6 +2072,20 @@ def test_copy_dangling_symlink(self):
         self.assertTrue(target2.joinpath('link').is_symlink())
         self.assertEqual(target2.joinpath('link').readlink(), self.cls('nonexistent'))
 
+    def test_copy_into(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        target_dir = base / 'dirA'
+        result = source.copy_into(target_dir)
+        self.assertEqual(result, target_dir / 'fileA')
+        self.assertTrue(result.exists())
+        self.assertEqual(source.read_text(), result.read_text())
+
+    def test_copy_into_empty_name(self):
+        source = self.cls('')
+        target_dir = self.base
+        self.assertRaises(ValueError, source.copy_into, target_dir)
+
     def test_move_file(self):
         base = self.cls(self.base)
         source = base / 'fileA'
@@ -2191,6 +2205,22 @@ def test_move_dangling_symlink(self):
         self.assertTrue(target.is_symlink())
         self.assertEqual(source_readlink, target.readlink())
 
+    def test_move_into(self):
+        base = self.cls(self.base)
+        source = base / 'fileA'
+        source_text = source.read_text()
+        target_dir = base / 'dirA'
+        result = source.move_into(target_dir)
+        self.assertEqual(result, target_dir / 'fileA')
+        self.assertFalse(source.exists())
+        self.assertTrue(result.exists())
+        self.assertEqual(source_text, result.read_text())
+
+    def test_move_into_empty_name(self):
+        source = self.cls('')
+        target_dir = self.base
+        self.assertRaises(ValueError, source.move_into, target_dir)
+
     def test_iterdir(self):
         P = self.cls
         p = P(self.base)

Misc/NEWS.d/next/Library/2024-08-25-16-59-20.gh-issue-73991.1w8u3K.rst

@@ -0,0 +1,2 @@
+Add :meth:`pathlib.Path.copy_into` and :meth:`~pathlib.Path.move_into`,
+which copy and move files and directories into *existing* directories.