bpo-43012: remove `pathlib._Accessor` (GH-25701)

Per Pitrou:

> The original intent for the “accessor” thing was to have a variant that did all accesses under a filesystem tree in a race condition-free way using openat and friends. It turned out to be much too hairy to actually implement, so was entirely abandoned, but the accessor abstraction was left there.

https://discuss.python.org/t/make-pathlib-extensible/3428/2

Accessors are:

- Lacking any internal purpose - '_NormalAccessor' is the only implementation
- Lacking any firm conceptual difference to `Path` objects themselves (inc. subclasses)
- Non-public, i.e. underscore prefixed - '_Accessor' and '_NormalAccessor' 
- Unofficially used to implement customized `Path` objects, but once once [bpo-24132]() is addressed there will be a supported route for that.

This patch preserves all existing behaviour.

2 files changed, 76 insertions, 130 deletions

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 1603325..920e1f4 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -275,93 +275,6 @@ _windows_flavour = _WindowsFlavour()
 _posix_flavour = _PosixFlavour()
 
 
-class _Accessor:
-    """An accessor implements a particular (system-specific or not) way of
-    accessing paths on the filesystem."""
-
-
-class _NormalAccessor(_Accessor):
-
-    stat = os.stat
-
-    open = io.open
-
-    listdir = os.listdir
-
-    scandir = os.scandir
-
-    chmod = os.chmod
-
-    mkdir = os.mkdir
-
-    unlink = os.unlink
-
-    if hasattr(os, "link"):
-        link = os.link
-    else:
-        def link(self, src, dst):
-            raise NotImplementedError("os.link() not available on this system")
-
-    rmdir = os.rmdir
-
-    rename = os.rename
-
-    replace = os.replace
-
-    if hasattr(os, "symlink"):
-        symlink = os.symlink
-    else:
-        def symlink(self, src, dst, target_is_directory=False):
-            raise NotImplementedError("os.symlink() not available on this system")
-
-    def touch(self, path, mode=0o666, exist_ok=True):
-        if exist_ok:
-            # First try to bump modification time
-            # Implementation note: GNU touch uses the UTIME_NOW option of
-            # the utimensat() / futimens() functions.
-            try:
-                os.utime(path, None)
-            except OSError:
-                # Avoid exception chaining
-                pass
-            else:
-                return
-        flags = os.O_CREAT | os.O_WRONLY
-        if not exist_ok:
-            flags |= os.O_EXCL
-        fd = os.open(path, flags, mode)
-        os.close(fd)
-
-    if hasattr(os, "readlink"):
-        readlink = os.readlink
-    else:
-        def readlink(self, path):
-            raise NotImplementedError("os.readlink() not available on this system")
-
-    def owner(self, path):
-        try:
-            import pwd
-            return pwd.getpwuid(self.stat(path).st_uid).pw_name
-        except ImportError:
-            raise NotImplementedError("Path.owner() is unsupported on this system")
-
-    def group(self, path):
-        try:
-            import grp
-            return grp.getgrgid(self.stat(path).st_gid).gr_name
-        except ImportError:
-            raise NotImplementedError("Path.group() is unsupported on this system")
-
-    getcwd = os.getcwd
-
-    expanduser = staticmethod(os.path.expanduser)
-
-    realpath = staticmethod(os.path.realpath)
-
-
-_normal_accessor = _NormalAccessor()
-
-
 #
 # Globbing helpers
 #
@@ -402,7 +315,7 @@ class _Selector:
         path_cls = type(parent_path)
         is_dir = path_cls.is_dir
         exists = path_cls.exists
-        scandir = parent_path._accessor.scandir
+        scandir = path_cls._scandir
         if not is_dir(parent_path):
             return iter([])
         return self._select_from(parent_path, is_dir, exists, scandir)
@@ -949,7 +862,6 @@ class Path(PurePath):
     object. You can also instantiate a PosixPath or WindowsPath directly,
     but cannot instantiate a WindowsPath on a POSIX system or vice versa.
     """
-    _accessor = _normal_accessor
     __slots__ = ()
 
     def __new__(cls, *args, **kwargs):
@@ -988,7 +900,7 @@ class Path(PurePath):
         """Return a new path pointing to the current working directory
         (as returned by os.getcwd()).
         """
-        return cls(cls._accessor.getcwd())
+        return cls(os.getcwd())
 
     @classmethod
     def home(cls):
@@ -1005,16 +917,22 @@ class Path(PurePath):
         try:
             other_st = other_path.stat()
         except AttributeError:
-            other_st = self._accessor.stat(other_path)
+            other_st = self.__class__(other_path).stat()
         return os.path.samestat(st, other_st)
 
     def iterdir(self):
         """Iterate over the files in this directory.  Does not yield any
         result for the special paths '.' and '..'.
         """
-        for name in self._accessor.listdir(self):
+        for name in os.listdir(self):
             yield self._make_child_relpath(name)
 
+    def _scandir(self):
+        # bpo-24132: a future version of pathlib will support subclassing of
+        # pathlib.Path to customize how the filesystem is accessed. This
+        # includes scandir(), which is used to implement glob().
+        return os.scandir(self)
+
     def glob(self, pattern):
         """Iterate over this subtree and yield all existing files (of any
         kind, including directories) matching the given relative pattern.
@@ -1050,7 +968,7 @@ class Path(PurePath):
         """
         if self.is_absolute():
             return self
-        return self._from_parts([self._accessor.getcwd()] + self._parts)
+        return self._from_parts([self.cwd()] + self._parts)
 
     def resolve(self, strict=False):
         """
@@ -1064,7 +982,7 @@ class Path(PurePath):
                 raise RuntimeError("Symlink loop from %r" % e.filename)
 
         try:
-            s = self._accessor.realpath(self, strict=strict)
+            s = os.path.realpath(self, strict=strict)
         except OSError as e:
             check_eloop(e)
             raise
@@ -1084,19 +1002,28 @@ class Path(PurePath):
         Return the result of the stat() system call on this path, like
         os.stat() does.
         """
-        return self._accessor.stat(self, follow_symlinks=follow_symlinks)
+        return os.stat(self, follow_symlinks=follow_symlinks)
 
     def owner(self):
         """
         Return the login name of the file owner.
         """
-        return self._accessor.owner(self)
+        try:
+            import pwd
+            return pwd.getpwuid(self.stat().st_uid).pw_name
+        except ImportError:
+            raise NotImplementedError("Path.owner() is unsupported on this system")
 
     def group(self):
         """
         Return the group name of the file gid.
         """
-        return self._accessor.group(self)
+
+        try:
+            import grp
+            return grp.getgrgid(self.stat().st_gid).gr_name
+        except ImportError:
+            raise NotImplementedError("Path.group() is unsupported on this system")
 
     def open(self, mode='r', buffering=-1, encoding=None,
              errors=None, newline=None):
@@ -1106,8 +1033,7 @@ class Path(PurePath):
         """
         if "b" not in mode:
             encoding = io.text_encoding(encoding)
-        return self._accessor.open(self, mode, buffering, encoding, errors,
-                                   newline)
+        return io.open(self, mode, buffering, encoding, errors, newline)
 
     def read_bytes(self):
         """
@@ -1148,21 +1074,38 @@ class Path(PurePath):
         """
         Return the path to which the symbolic link points.
         """
-        path = self._accessor.readlink(self)
-        return self._from_parts((path,))
+        if not hasattr(os, "readlink"):
+            raise NotImplementedError("os.readlink() not available on this system")
+        return self._from_parts((os.readlink(self),))
 
     def touch(self, mode=0o666, exist_ok=True):
         """
         Create this file with the given access mode, if it doesn't exist.
         """
-        self._accessor.touch(self, mode, exist_ok)
+
+        if exist_ok:
+            # First try to bump modification time
+            # Implementation note: GNU touch uses the UTIME_NOW option of
+            # the utimensat() / futimens() functions.
+            try:
+                os.utime(self, None)
+            except OSError:
+                # Avoid exception chaining
+                pass
+            else:
+                return
+        flags = os.O_CREAT | os.O_WRONLY
+        if not exist_ok:
+            flags |= os.O_EXCL
+        fd = os.open(self, flags, mode)
+        os.close(fd)
 
     def mkdir(self, mode=0o777, parents=False, exist_ok=False):
         """
         Create a new directory at this given path.
         """
         try:
-            self._accessor.mkdir(self, mode)
+            os.mkdir(self, mode)
         except FileNotFoundError:
             if not parents or self.parent == self:
                 raise
@@ -1178,7 +1121,7 @@ class Path(PurePath):
         """
         Change the permissions of the path, like os.chmod().
         """
-        self._accessor.chmod(self, mode, follow_symlinks=follow_symlinks)
+        os.chmod(self, mode, follow_symlinks=follow_symlinks)
 
     def lchmod(self, mode):
         """
@@ -1193,7 +1136,7 @@ class Path(PurePath):
         If the path is a directory, use rmdir() instead.
         """
         try:
-            self._accessor.unlink(self)
+            os.unlink(self)
         except FileNotFoundError:
             if not missing_ok:
                 raise
@@ -1202,7 +1145,7 @@ class Path(PurePath):
         """
         Remove this directory.  The directory must be empty.
         """
-        self._accessor.rmdir(self)
+        os.rmdir(self)
 
     def lstat(self):
         """
@@ -1221,7 +1164,7 @@ class Path(PurePath):
 
         Returns the new Path instance pointing to the target path.
         """
-        self._accessor.rename(self, target)
+        os.rename(self, target)
         return self.__class__(target)
 
     def replace(self, target):
@@ -1234,7 +1177,7 @@ class Path(PurePath):
 
         Returns the new Path instance pointing to the target path.
         """
-        self._accessor.replace(self, target)
+        os.replace(self, target)
         return self.__class__(target)
 
     def symlink_to(self, target, target_is_directory=False):
@@ -1242,7 +1185,9 @@ class Path(PurePath):
         Make this path a symlink pointing to the target path.
         Note the order of arguments (link, target) is the reverse of os.symlink.
         """
-        self._accessor.symlink(target, self, target_is_directory)
+        if not hasattr(os, "symlink"):
+            raise NotImplementedError("os.symlink() not available on this system")
+        os.symlink(target, self, target_is_directory)
 
     def hardlink_to(self, target):
         """
@@ -1250,7 +1195,9 @@ class Path(PurePath):
 
         Note the order of arguments (self, target) is the reverse of os.link's.
         """
-        self._accessor.link(target, self)
+        if not hasattr(os, "link"):
+            raise NotImplementedError("os.link() not available on this system")
+        os.link(target, self)
 
     def link_to(self, target):
         """
@@ -1268,7 +1215,7 @@ class Path(PurePath):
                       "for removal in Python 3.12. "
                       "Use pathlib.Path.hardlink_to() instead.",
                       DeprecationWarning, stacklevel=2)
-        self._accessor.link(self, target)
+        self.__class__(target).hardlink_to(self)
 
     # Convenience functions for querying the stat results
 
@@ -1425,7 +1372,7 @@ class Path(PurePath):
         """
         if (not (self._drv or self._root) and
             self._parts and self._parts[0][:1] == '~'):
-            homedir = self._accessor.expanduser(self._parts[0])
+            homedir = os.path.expanduser(self._parts[0])
             if homedir[:1] == "~":
                 raise RuntimeError("Could not determine home directory.")
             return self._from_parts([homedir] + self._parts[1:])
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 3fbf1d1..5e46b4f 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -1,3 +1,4 @@
+import contextlib
 import collections.abc
 import io
 import os
@@ -1459,7 +1460,7 @@ class _BasePathTest(object):
     def test_absolute_common(self):
         P = self.cls
 
-        with mock.patch("pathlib._normal_accessor.getcwd") as getcwd:
+        with mock.patch("os.getcwd") as getcwd:
             getcwd.return_value = BASE
 
             # Simple relative paths.
@@ -1738,21 +1739,18 @@ class _BasePathTest(object):
         # Patching is needed to avoid relying on the filesystem
         # to return the order of the files as the error will not
         # happen if the symlink is the last item.
-
-        with mock.patch("os.scandir") as scandir:
-            scandir.return_value = sorted(os.scandir(base))
+        real_scandir = os.scandir
+        def my_scandir(path):
+            with real_scandir(path) as scandir_it:
+                entries = list(scandir_it)
+            entries.sort(key=lambda entry: entry.name)
+            return contextlib.nullcontext(entries)
+
+        with mock.patch("os.scandir", my_scandir):
             self.assertEqual(len(set(base.glob("*"))), 3)
-
-        subdir.mkdir()
-
-        with mock.patch("os.scandir") as scandir:
-            scandir.return_value = sorted(os.scandir(base))
+            subdir.mkdir()
             self.assertEqual(len(set(base.glob("*"))), 4)
-
-        subdir.chmod(000)
-
-        with mock.patch("os.scandir") as scandir:
-            scandir.return_value = sorted(os.scandir(base))
+            subdir.chmod(000)
             self.assertEqual(len(set(base.glob("*"))), 4)
 
     def _check_resolve(self, p, expected, strict=True):
@@ -2199,6 +2197,7 @@ class _BasePathTest(object):
             p = self.cls(BASE, 'dirCPC%d' % pattern_num)
             self.assertFalse(p.exists())
 
+            real_mkdir = os.mkdir
             def my_mkdir(path, mode=0o777):
                 path = str(path)
                 # Emulate another process that would create the directory
@@ -2207,15 +2206,15 @@ class _BasePathTest(object):
                 # function is called at most 5 times (dirCPC/dir1/dir2,
                 # dirCPC/dir1, dirCPC, dirCPC/dir1, dirCPC/dir1/dir2).
                 if pattern.pop():
-                    os.mkdir(path, mode)  # From another process.
+                    real_mkdir(path, mode)  # From another process.
                     concurrently_created.add(path)
-                os.mkdir(path, mode)  # Our real call.
+                real_mkdir(path, mode)  # Our real call.
 
             pattern = [bool(pattern_num & (1 << n)) for n in range(5)]
             concurrently_created = set()
             p12 = p / 'dir1' / 'dir2'
             try:
-                with mock.patch("pathlib._normal_accessor.mkdir", my_mkdir):
+                with mock.patch("os.mkdir", my_mkdir):
                     p12.mkdir(parents=True, exist_ok=False)
             except FileExistsError:
                 self.assertIn(str(p12), concurrently_created)
@@ -2676,7 +2675,7 @@ class WindowsPathTest(_BasePathTest, unittest.TestCase):
         self.assertEqual(str(P(share + 'a\\b').absolute()), share + 'a\\b')
 
         # UNC relative paths.
-        with mock.patch("pathlib._normal_accessor.getcwd") as getcwd:
+        with mock.patch("os.getcwd") as getcwd:
             getcwd.return_value = share
 
             self.assertEqual(str(P().absolute()), share)