GH-117727: Speed up `pathlib.Path.iterdir()` by using `os.scandir()` (#117728)

Replace use of `os.listdir()` with `os.scandir()`. Forgo setting `_drv`,
`_root` and `_tail_cached`, as these usually aren't needed. Use
`os.DirEntry.path` to set `_str`.

2 files changed, 8 insertions, 20 deletions

diff --git a/Lib/pathlib/__init__.py b/Lib/pathlib/__init__.py
index 746cbcd..66eb08a 100644
--- a/Lib/pathlib/__init__.py
+++ b/Lib/pathlib/__init__.py
@@ -584,26 +584,12 @@ class Path(_abc.PathBase, PurePath):
         The children are yielded in arbitrary order, and the
         special entries '.' and '..' are not included.
         """
-        return (self._make_child_relpath(name) for name in os.listdir(self))
-
-
-    def _make_child_relpath(self, name):
-        if not name:
-            return self
-        path_str = str(self)
-        tail = self._tail
-        if tail:
-            path_str = f'{path_str}{self.parser.sep}{name}'
-        elif path_str != '.':
-            path_str = f'{path_str}{name}'
-        else:
-            path_str = name
-        path = self.with_segments(path_str)
-        path._str = path_str
-        path._drv = self.drive
-        path._root = self.root
-        path._tail_cached = tail + [name]
-        return path
+        root_dir = str(self)
+        with os.scandir(root_dir) as scandir_it:
+            paths = [entry.path for entry in scandir_it]
+        if root_dir == '.':
+            paths = map(self._remove_leading_dot, paths)
+        return map(self._from_parsed_string, paths)
 
     def glob(self, pattern, *, case_sensitive=None, recurse_symlinks=False):
         """Iterate over this subtree and yield all existing files (of any
diff --git a/Misc/NEWS.d/next/Library/2024-04-10-21-30-37.gh-issue-117727.uAYNVS.rst b/Misc/NEWS.d/next/Library/2024-04-10-21-30-37.gh-issue-117727.uAYNVS.rst
new file mode 100644
index 0000000..3a0b683
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-04-10-21-30-37.gh-issue-117727.uAYNVS.rst
@@ -0,0 +1,2 @@
+Speed up :meth:`pathlib.Path.iterdir` by using :func:`os.scandir`
+internally.