bpo-1154351: Add get_current_dir_name() to os module

Doc/library/os.rst

@@ -155,6 +155,7 @@ process and user.
 .. function:: chdir(path)
               fchdir(fd)
               getcwd()
+              get_current_dir_name()
    :noindex:
 
    These functions are described in :ref:`os-file-dir`.
@@ -1698,6 +1699,17 @@ features:
    Return a bytestring representing the current working directory.
 
 
+.. function:: get_current_dir_name()
+
+    Return a string representing the current working directory taking into
+    consideration the users :envvar:`PWD` environment variable if it exists. This is
+    opposed to :func:`getcwd` which dereferences symlinks in the path. This
+    function is identical to :func:`getcwd` on systems that do **not**
+    support the :envvar:`PWD` environment variable.
+
+    .. versionadded:: 3.8
+
+
 .. function:: lchflags(path, flags)
 
    Set the flags of *path* to the numeric *flags*, like :func:`chflags`, but do

Doc/whatsnew/3.8.rst

@@ -141,6 +141,12 @@ by right-clicking the button.  (Contributed by Tal Einat in :issue:`1529353`.)
 The changes above have been backported to 3.7 maintenance releases.
 
 
+os
+--
+
+Added :func:`~os.get_current_dir_name` function.
+(Contributed by Braden Groom in :issue:`1154351`.)
+
 os.path
 -------
 

Lib/os.py

@@ -32,7 +32,7 @@
 __all__ = ["altsep", "curdir", "pardir", "sep", "pathsep", "linesep",
            "defpath", "name", "path", "devnull", "SEEK_SET", "SEEK_CUR",
            "SEEK_END", "fsencode", "fsdecode", "get_exec_path", "fdopen",
-           "popen", "extsep"]
+           "popen", "extsep", "get_current_dir_name"]
 
 def _exists(name):
     return name in globals()
@@ -651,6 +651,26 @@ def get_exec_path(env=None):
     return path_list.split(pathsep)
 
 
+def get_current_dir_name():
+    """
+    Return a string representing the current working directory taking into
+    consideration the users *PWD* environment variable if it exists. This
+    is opposed to getcwd() which dereferences symlinks in the path. This
+    function is identical to getcwd() on systems that do *not* support
+    the *PWD* environment variable.
+    """
+    cwd = getcwd()
+    if name == 'nt':
+        return cwd
+    try:
+        pwd = environ["PWD"]
+    except KeyError:
+        return cwd
+    if path.samefile(cwd, pwd):
+        return pwd
+    return cwd
+
+
 # Change environ to automatically call putenv(), unsetenv if they exist.
 from _collections_abc import MutableMapping
 

Lib/test/test_os.py

@@ -28,6 +28,7 @@
 import uuid
 import warnings
 from test import support
+from unittest import mock
 
 try:
     import resource
@@ -1252,6 +1253,48 @@ def tearDownClass(cls):
         os.rmdir(support.TESTFN)
 
 
+class CurrentDirTests(unittest.TestCase):
+
+    def setUp(self):
+        base = os.path.abspath(support.TESTFN)
+        self.tmp_dir = base + '_dir'
+        self.tmp_lnk = base + '_lnk'
+
+    def test_getcwd(self):
+        # os.getcwd() always returns the dereferenced path
+        with support.temp_cwd(self.tmp_dir):
+            os.chdir(self.tmp_dir)
+            self.assertEqual(os.getcwd(), self.tmp_dir)
+            self.addCleanup(support.unlink, self.tmp_lnk)
+            os.symlink(self.tmp_dir, self.tmp_lnk, True)
+            os.chdir(self.tmp_lnk)
+            if os.name == 'nt':
+                # windows doesn't dereference the path
+                expected_cwd = self.tmp_lnk
+            else:
+                expected_cwd = self.tmp_dir
+            self.assertEqual(os.getcwd(), expected_cwd)
+            with mock.patch.dict('os.environ', {'PWD': self.tmp_dir}):
+                self.assertEqual(os.getcwd(), expected_cwd)
+            with mock.patch.dict('os.environ', {'PWD': self.tmp_lnk}):
+                self.assertEqual(os.getcwd(), expected_cwd)
+
+    def test_get_current_dir_name(self):
+        # os.get_current_dir_name() returns the direct path--mirroring
+        # the PWD environment variable if it exists regardless of
+        # whether the path contains symlinks.
+        with support.temp_cwd(self.tmp_dir):
+            with mock.patch.dict('os.environ', {'PWD': self.tmp_dir}):
+                self.assertEqual(os.get_current_dir_name(), self.tmp_dir)
+            self.addCleanup(support.unlink, self.tmp_lnk)
+            os.symlink(self.tmp_dir, self.tmp_lnk, True)
+            with mock.patch.dict('os.environ', {'PWD': self.tmp_lnk}):
+                if os.name == 'posix':
+                    self.assertEqual(os.get_current_dir_name(), self.tmp_lnk)
+                else:
+                    self.assertEqual(os.get_current_dir_name(), self.tmp_dir)
+
+
 class RemoveDirsTests(unittest.TestCase):
     def setUp(self):
         os.makedirs(support.TESTFN)

Misc/NEWS.d/next/Library/2018-10-25-19-44-42.bpo-1154351.KhXLos.rst

@@ -0,0 +1,2 @@
+Add get_current_dir_name() to the os module.
+Patch by Braden Groom