bpo-34137: Add pathlib.Path.lexists and related

This adds the `follow_symlink` parameter to `pathlib.Path.exists()`,
and wraps the new functionality in `pathlib.Path.lexists()`, analogous
to `os.stat()` ./. `os.lstat()` and `os.path.exists()` ./.
`os.path.lexists()`.

GH-NNNN

Signed-off-by: Nils Philippsen <[email protected]>

Author: nphilipp

Doc/library/pathlib.rst

@@ -739,7 +739,7 @@ call fails (for example because the path doesn't exist).
       33060
 
 
-.. method:: Path.exists()
+.. method:: Path.exists(*, follow_symlinks=True)
 
    Whether the path points to an existing file or directory::
 
@@ -754,7 +754,11 @@ call fails (for example because the path doesn't exist).
 
    .. note::
       If the path points to a symlink, :meth:`exists` returns whether the
-      symlink *points to* an existing file or directory.
+      symlink *points to* an existing file or directory, unless
+      *follow_symlinks* is False.
+
+   .. versionchanged:: 3.10
+      The *follow_symlinks* parameter was added.
 
 
 .. method:: Path.expanduser()
@@ -903,6 +907,14 @@ call fails (for example because the path doesn't exist).
    symbolic link's mode is changed rather than its target's.
 
 
+.. method:: Path.lexists()
+
+   Like :meth:`Path.exists` but, if the path points to a symbolic link, return
+   the symbolic link's information rather than its target's.
+
+   .. versionadded:: 3.10
+
+
 .. method:: Path.lstat()
 
    Like :meth:`Path.stat` but, if the path points to a symbolic link, return
@@ -1219,6 +1231,7 @@ Below is a table mapping various :mod:`os` functions to their corresponding
 :func:`os.path.isdir`                  :meth:`Path.is_dir`
 :func:`os.path.isfile`                 :meth:`Path.is_file`
 :func:`os.path.islink`                 :meth:`Path.is_symlink`
+:func:`os.path.lexists`                :meth:`Path.lexists`
 :func:`os.link`                        :meth:`Path.link_to`
 :func:`os.symlink`                     :meth:`Path.symlink_to`
 :func:`os.readlink`                    :meth:`Path.readlink`

Lib/pathlib.py

@@ -1402,12 +1402,18 @@ def symlink_to(self, target, target_is_directory=False):
 
     # Convenience functions for querying the stat results
 
-    def exists(self):
+    def exists(self, *, follow_symlinks=True):
         """
         Whether this path exists.
+
+        Returns False for broken symbolic links unless follow_symlinks is set
+        to False.
         """
         try:
-            self.stat()
+            if follow_symlinks:
+                self.stat()
+            else:
+                self.lstat()
         except OSError as e:
             if not _ignore_error(e):
                 raise
@@ -1549,6 +1555,14 @@ def is_socket(self):
             # Non-encodable path
             return False
 
+    def lexists(self):
+        """
+        Whether this path exists, but don't follow symbolic links.
+
+        Returns True for broken symbolic links.
+        """
+        return self.exists(follow_symlinks=False)
+
     def expanduser(self):
         """ Return a new path with expanded ~ and ~user constructs
         (as returned by os.path.expanduser)

Lib/test/test_pathlib.py

@@ -1509,11 +1509,31 @@ def test_exists(self):
             self.assertIs(True, (p / 'linkB').exists())
             self.assertIs(True, (p / 'linkB' / 'fileB').exists())
             self.assertIs(False, (p / 'linkA' / 'bah').exists())
+            self.assertIs(False, (p / 'brokenLink').exists())
+            self.assertIs(False, (p / 'brokenLinkLoop').exists())
+            self.assertIs(True, (p / 'brokenLink').exists(
+                follow_symlinks=False))
+            self.assertIs(True, (p / 'brokenLinkLoop').exists(
+                follow_symlinks=False))
         self.assertIs(False, (p / 'foo').exists())
         self.assertIs(False, P('/xyzzy').exists())
         self.assertIs(False, P(BASE + '\udfff').exists())
         self.assertIs(False, P(BASE + '\x00').exists())
 
+    @os_helper.skip_unless_symlink
+    def test_exists_follow_symlinks(self):
+        P = self.cls
+        p = P(BASE)
+        self.assertIs(True, (p / 'brokenLink').exists(follow_symlinks=False))
+        self.assertIs(True, (p / 'brokenLinkLoop').exists(follow_symlinks=False))
+
+    @os_helper.skip_unless_symlink
+    def test_lexists(self):
+        P = self.cls
+        p = P(BASE)
+        self.assertIs(True, (p / 'brokenLink').lexists())
+        self.assertIs(True, (p / 'brokenLinkLoop').lexists())
+
     def test_open_common(self):
         p = self.cls(BASE)
         with (p / 'fileA').open('r') as f:

Misc/NEWS.d/next/Library/2020-06-25-16-34-59.bpo-34137.JomN6i.rst

@@ -0,0 +1,4 @@
+Add the *follow_symlinks* parameter in :meth:`pathlib.Path.exists` and
+:meth:`pathlib.Path.lexists` as a wrapper analogous to
+:func:`os.stat` ./. :func:`os.lstat` and
+:func:`os.path.exists` ./. :func:`os.path.lexists`.