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