GH-104996: Defer joining of pathlib.PurePath() arguments.

Lib/pathlib.py

@@ -195,10 +195,10 @@ def _select_unique(paths):
  yielded = set()
  try:
  for path in paths:
-raw_path = path._raw_path
- if raw_path not in yielded:
+path_str = str(path)
+ if path_str not in yielded:
  yield path
- yielded.add(raw_path)
+ yielded.add(path_str)
  finally:
  yielded.clear()
 
@@ -247,9 +247,9 @@ class PurePath:
  """
 
  __slots__ = (
- # The `_raw_path` slot stores an unnormalized string path. This is set
+ # The `_raw_paths` slot stores unnormalized string paths. This is set
  # in the `__init__()` method.
- '_raw_path',
+ '_raw_paths',
 
  # The `_drv`, `_root` and `_tail_cached` slots store parsed and
  # normalized parts of the path. They are set when any of the `drive`,
@@ -306,10 +306,11 @@ def __init__(self, *args):
  paths = []
  for arg in args:
  if isinstance(arg, PurePath):
- path = arg._raw_path
  if arg._flavour is ntpath and self._flavour is posixpath:
  # GH-103631: Convert separators for backwards compatibility.
- path = path.replace('\\', '/')
+ paths.extend(path.replace('\\', '/') for path in arg._raw_paths)
+ else:
+ paths.extend(arg._raw_paths)
  else:
  try:
  path = os.fspath(arg)
@@ -320,13 +321,8 @@ def __init__(self, *args):
  "argument should be a str or an os.PathLike "
  "object where __fspath__ returns a str, "
  f"not {type(path).__name__!r}")
- paths.append(path)
- if len(paths) == 0:
- self._raw_path = ''
- elif len(paths) == 1:
- self._raw_path = paths[0]
- else:
- self._raw_path = self._flavour.join(*paths)
+ paths.append(path)
+ self._raw_paths = paths
 
  def with_segments(self, *pathsegments):
  """Construct a new path object from any number of path-like objects.
@@ -356,7 +352,14 @@ def _parse_path(cls, path):
  return drv, root, parsed
 
  def _load_parts(self):
- drv, root, tail = self._parse_path(self._raw_path)
+ paths = self._raw_paths
+ if len(paths) == 0:
+ path = ''
+ elif len(paths) == 1:
+ path = paths[0]
+ else:
+ path = self._flavour.join(*paths)
+ drv, root, tail = self._parse_path(path)
  self._drv = drv
  self._root = root
  self._tail_cached = tail
@@ -687,10 +690,17 @@ def parents(self):
  def is_absolute(self):
  """True if the path is absolute (has both a root and, if applicable,
  a drive)."""
- # ntpath.isabs() is defective - see GH-44626 .
  if self._flavour is ntpath:
+ # ntpath.isabs() is defective - see GH-44626.
  return bool(self.drive and self.root)
- return self._flavour.isabs(self._raw_path)
+ elif self._flavour is posixpath:
+ # Optimization: work with raw paths on POSIX.
+ for path in self._raw_paths:
+ if path.startswith('/'):
+ return True
+ return False
+ else:
+ return self._flavour.isabs(str(self))
 
  def is_reserved(self):
  """Return True if the path contains one of the special names reserved

Misc/NEWS.d/next/Library/2023-05-26-21-24-06.gh-issue-104996.aaW78g.rst

@@ -0,0 +1,2 @@
+Improve performance of :class:`pathlib.PurePath` initialisation by
+deferring joining of paths when multiple arguments are given.