Speed up path construction when recursing

Author: barneygale

Lib/pathlib/_abc.py

@@ -166,7 +166,7 @@ def copy_dir(self, source, target, metadata_keys, dir_entry=None):
         with source.scandir() as entries:
             target.mkdir(exist_ok=self.dirs_exist_ok)
             for entry in entries:
-                src = source.joinpath(entry.name)
+                src = source._join_dir_entry(entry)
                 dst = target.joinpath(entry.name)
                 if not self.follow_symlinks and entry.is_symlink():
                     self.copy_symlink(src, dst, metadata_keys, entry)
@@ -720,6 +720,12 @@ def write_text(self, data, encoding=None, errors=None, newline=None):
         with self.open(mode='w', encoding=encoding, errors=errors, newline=newline) as f:
             return f.write(data)
 
+    def _join_dir_entry(self, dir_entry):
+        """Construct a new path object from the given os.DirEntry-like object,
+        which should have been generated by calling scandir() on this path.
+        """
+        return self.joinpath(dir_entry.name)
+
     def scandir(self):
         """Yield os.DirEntry objects of the directory contents.
 
@@ -735,8 +741,8 @@ def iterdir(self):
         special entries '.' and '..' are not included.
         """
         with self.scandir() as entries:
-            names = [entry.name for entry in entries]
-        return map(self.joinpath, names)
+            entries = list(entries)
+        return map(self._join_dir_entry, entries)
 
     def _glob_selector(self, parts, case_sensitive, recurse_symlinks):
         if case_sensitive is None:
@@ -792,7 +798,7 @@ def walk(self, top_down=True, on_error=None, follow_symlinks=False):
                         try:
                             if entry.is_dir(follow_symlinks=follow_symlinks):
                                 if not top_down:
-                                    paths.append(path.joinpath(name))
+                                    paths.append(path._join_dir_entry(entry))
                                 dirnames.append(name)
                             else:
                                 filenames.append(name)

Lib/pathlib/_local.py

@@ -647,6 +647,12 @@ def _filter_trailing_slash(self, paths):
                 path_str = path_str[:-1]
             yield path_str
 
+    def _join_dir_entry(self, dir_entry):
+        path_str = dir_entry.name if str(self) == '.' else dir_entry.path
+        path = self.with_segments(path_str)
+        path._str = path_str
+        return path
+
     def scandir(self):
         """Yield os.DirEntry objects of the directory contents.
 
@@ -655,19 +661,6 @@ def scandir(self):
         """
         return os.scandir(self)
 
-    def iterdir(self):
-        """Yield path objects of the directory contents.
-
-        The children are yielded in arbitrary order, and the
-        special entries '.' and '..' are not included.
-        """
-        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
         kind, including directories) matching the given relative pattern.