python · barneygale · Jan 27, 2023 · Feb 4, 2023 · Feb 4, 2023 · Feb 4, 2023
diff --git a/Lib/pathlib.py b/Lib/pathlib.py
@@ -16,7 +16,6 @@
 import warnings
 from _collections_abc import Sequence
 from errno import ENOENT, ENOTDIR, EBADF, ELOOP
-from operator import attrgetter
 from stat import S_ISDIR, S_ISLNK, S_ISREG, S_ISSOCK, S_ISBLK, S_ISCHR, S_ISFIFO
 from urllib.parse import quote_from_bytes as urlquote_from_bytes
 
@@ -216,8 +215,8 @@ class _PathParents(Sequence):
     def __init__(self, path):
         # We don't store the instance to avoid reference cycles
         self._pathcls = type(path)
-        self._drv = path._drv
-        self._root = path._root
+        self._drv = path.drive
+        self._root = path.root
         self._parts = path._parts
 
     def __len__(self):
@@ -251,7 +250,7 @@ class PurePath(object):
     directly, regardless of your system.
     """
     __slots__ = (
-        '_drv', '_root', '_parts',
+        '_fspath', '_drv', '_root', '_parts_cached',
         '_str', '_hash', '_parts_tuple', '_parts_normcase_cached',
     )
     _flavour = os.path
@@ -269,18 +268,16 @@ def __new__(cls, *args):
     def __reduce__(self):
         # Using the parts tuple helps share interned path parts
         # when pickling related paths.
-        return (self.__class__, tuple(self._parts))
+        return (self.__class__, self.parts)
 
     @classmethod
-    def _parse_parts(cls, parts):
+    def _from_parts(cls, parts):
         if not parts:
-            return '', '', []
+            path = ''
         elif len(parts) == 1:
             path = os.fspath(parts[0])
         else:
             path = cls._flavour.join(*parts)
-        sep = cls._flavour.sep
-        altsep = cls._flavour.altsep
         if isinstance(path, str):
             # Force-cast str subclasses to str (issue #21127)
             path = str(path)
@@ -289,6 +286,16 @@ def _parse_parts(cls, parts):
                 "argument should be a str or an os.PathLike "
                 "object where __fspath__ returns a str, "
                 f"not {type(path).__name__!r}")
+        self = object.__new__(cls)
+        self._fspath = path
+        return self
+
+    @classmethod
+    def _parse_path(cls, path):
+        if not path:
+            return '', '', []
+        sep = cls._flavour.sep
+        altsep = cls._flavour.altsep
         if altsep:
             path = path.replace(altsep, sep)
         drv, root, rel = cls._flavour.splitroot(path)
@@ -299,21 +306,18 @@ def _parse_parts(cls, parts):
         parsed = [sys.intern(x) for x in unfiltered_parsed if x and x != '.']
         return drv, root, parsed
 
-    @classmethod
-    def _from_parts(cls, args):
-        self = object.__new__(cls)
-        drv, root, parts = self._parse_parts(args)
+    def _load_parts(self):
+        drv, root, parts = self._parse_path(self._fspath)
         self._drv = drv
         self._root = root
-        self._parts = parts
-        return self
+        self._parts_cached = parts
 
     @classmethod
     def _from_parsed_parts(cls, drv, root, parts):
         self = object.__new__(cls)
         self._drv = drv
         self._root = root
-        self._parts = parts
+        self._parts_cached = parts
         return self
 
     @classmethod
@@ -330,7 +334,7 @@ def __str__(self):
         try:
             return self._str
         except AttributeError:
-            self._str = self._format_parsed_parts(self._drv, self._root,
+            self._str = self._format_parsed_parts(self.drive, self.root,
                                                   self._parts) or '.'
             return self._str
 
@@ -356,7 +360,7 @@ def as_uri(self):
         if not self.is_absolute():
             raise ValueError("relative path can't be expressed as a file URI")
 
-        drive = self._drv
+        drive = self.drive
         if len(drive) == 2 and drive[1] == ':':
             # It's a path on a local drive => 'file:///c:/a/b'
             prefix = 'file:///' + drive
@@ -412,23 +416,43 @@ def __ge__(self, other):
             return NotImplemented
         return self._parts_normcase >= other._parts_normcase
 
-    drive = property(attrgetter('_drv'),
-                     doc="""The drive prefix (letter or UNC path), if any.""")
+    @property
+    def drive(self):
+        """The drive prefix (letter or UNC path), if any."""
+        try:
+            return self._drv
+        except AttributeError:
+            self._load_parts()
+            return self._drv
 
-    root = property(attrgetter('_root'),
-                    doc="""The root of the path, if any.""")
+    @property
+    def root(self):
+        """The root of the path, if any."""
+        try:
+            return self._root
+        except AttributeError:
+            self._load_parts()
+            return self._root
+
+    @property
+    def _parts(self):
+        try:
+            return self._parts_cached
+        except AttributeError:
+            self._load_parts()
+            return self._parts_cached
 
     @property
     def anchor(self):
         """The concatenation of the drive and root, or ''."""
-        anchor = self._drv + self._root
+        anchor = self.drive + self.root
         return anchor
 
     @property
     def name(self):
         """The final path component, if any."""
         parts = self._parts
-        if len(parts) == (1 if (self._drv or self._root) else 0):
+        if len(parts) == (1 if (self.drive or self.root) else 0):
             return ''
         return parts[-1]
 
@@ -477,7 +501,7 @@ def with_name(self, name):
         drv, root, tail = f.splitroot(name)
         if drv or root or not tail or f.sep in tail or (f.altsep and f.altsep in tail):
             raise ValueError("Invalid name %r" % (name))
-        return self._from_parsed_parts(self._drv, self._root,
+        return self._from_parsed_parts(self.drive, self.root,
                                        self._parts[:-1] + [name])
 
     def with_stem(self, stem):
@@ -502,7 +526,7 @@ def with_suffix(self, suffix):
             name = name + suffix
         else:
             name = name[:-len(old_suffix)] + suffix
-        return self._from_parsed_parts(self._drv, self._root,
+        return self._from_parsed_parts(self.drive, self.root,
                                        self._parts[:-1] + [name])
 
     def relative_to(self, other, /, *_deprecated, walk_up=False):
@@ -593,8 +617,8 @@ def __rtruediv__(self, key):
     @property
     def parent(self):
         """The logical parent of the path."""
-        drv = self._drv
-        root = self._root
+        drv = self.drive
+        root = self.root
         parts = self._parts
         if len(parts) == 1 and (drv or root):
             return self
@@ -610,7 +634,7 @@ def is_absolute(self):
         a drive)."""
         # ntpath.isabs() is defective - see GH-44626 .
         if self._flavour is ntpath:
-            return bool(self._drv and self._root)
+            return bool(self.drive and self.root)
         return self._flavour.isabs(self)
 
     def is_reserved(self):
@@ -634,7 +658,7 @@ def match(self, path_pattern):
         Return True if this path matches the given pattern.
         """
         path_pattern = self._flavour.normcase(path_pattern)
-        drv, root, pat_parts = self._parse_parts((path_pattern,))
+        drv, root, pat_parts = self._parse_path(path_pattern)
         if not pat_parts:
             raise ValueError("empty pattern")
         parts = self._parts_normcase
@@ -700,7 +724,7 @@ def _make_child_relpath(self, part):
         # This is an optimization used for dir walking.  `part` must be
         # a single part relative to this path.
         parts = self._parts + [part]
-        return self._from_parsed_parts(self._drv, self._root, parts)
+        return self._from_parsed_parts(self.drive, self.root, parts)
 
     def __enter__(self):
         # In previous versions of pathlib, __exit__() marked this path as
@@ -770,7 +794,7 @@ def glob(self, pattern):
         sys.audit("pathlib.Path.glob", self, pattern)
         if not pattern:
             raise ValueError("Unacceptable pattern: {!r}".format(pattern))
-        drv, root, pattern_parts = self._parse_parts((pattern,))
+        drv, root, pattern_parts = self._parse_path(pattern)
         if drv or root:
             raise NotImplementedError("Non-relative patterns are unsupported")
         if pattern[-1] in (self._flavour.sep, self._flavour.altsep):
@@ -785,7 +809,7 @@ def rglob(self, pattern):
         this subtree.
         """
         sys.audit("pathlib.Path.rglob", self, pattern)
-        drv, root, pattern_parts = self._parse_parts((pattern,))
+        drv, root, pattern_parts = self._parse_path(pattern)
         if drv or root:
             raise NotImplementedError("Non-relative patterns are unsupported")
         if pattern and pattern[-1] in (self._flavour.sep, self._flavour.altsep):
@@ -802,9 +826,9 @@ def absolute(self):
         """
         if self.is_absolute():
             return self
-        elif self._drv:
+        elif self.drive:
             # There is a CWD on each drive-letter drive.
-            cwd = self._flavour.abspath(self._drv)
+            cwd = self._flavour.abspath(self.drive)
         else:
             cwd = os.getcwd()
         return self._from_parts([cwd] + self._parts)
@@ -1184,12 +1208,12 @@ def expanduser(self):
         """ Return a new path with expanded ~ and ~user constructs
         (as returned by os.path.expanduser)
         """
-        if (not (self._drv or self._root) and
+        if (not (self.drive or self.root) and
             self._parts and self._parts[0][:1] == '~'):
             homedir = self._flavour.expanduser(self._parts[0])
             if homedir[:1] == "~":
                 raise RuntimeError("Could not determine home directory.")
-            drv, root, parts = self._parse_parts((homedir,))
+            drv, root, parts = self._parse_path(homedir)
             return self._from_parsed_parts(drv, root, parts + self._parts[1:])
 
         return self

diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
@@ -26,7 +26,9 @@
 class _BaseFlavourTest(object):
 
     def _check_parse_parts(self, arg, expected):
-        f = self.cls._parse_parts
+        def f(parts):
+            path = self.flavour.join(*parts) if parts else ''
+            return self.cls._parse_path(path)
         sep = self.flavour.sep
         altsep = self.flavour.altsep
         actual = f([x.replace('/', sep) for x in arg])

diff --git a/Misc/NEWS.d/next/Library/2023-02-04-17-47-08.gh-issue-101362.uZjk9-.rst b/Misc/NEWS.d/next/Library/2023-02-04-17-47-08.gh-issue-101362.uZjk9-.rst
@@ -0,0 +1,2 @@
+Speed up construction of :class:`pathlib.PurePath` objects by deferring
+path parsing and normalization.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Speed up construction of :class:`pathlib.PurePath` objects by deferring
		path parsing and normalization.