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bpo-1154351: Add get_current_dir_name() to os module #10117

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1daae93
bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 26, 2018
ee4c4f6
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 26, 2018
f836691
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 26, 2018
89e1984
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 26, 2018
4bfb33c
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 27, 2018
963659a
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 27, 2018
cc1735f
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 27, 2018
d49fdf3
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 27, 2018
17386e1
fixup! bpo-1154351: add get_current_dir_name() to os module
bradengroom Oct 27, 2018
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14 changes: 14 additions & 0 deletions Doc/library/os.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -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`.
Expand Down Expand Up @@ -1698,6 +1699,19 @@ 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 ``PWD`` environment variable if it exists. This is
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Use :envvar:?

opposed to :func:`getcwd()` which dereferences symlinks in the path. This
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Remove (). It is added automatically.

function is identical to :func:`getcwd()` on systems that do **not**
support the ``PWD`` environment variable.

.. availability:: Unix.
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This function is available on all platforms.

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Actually, while this is undoubtably an ancient link ( https://www.gnu.org/software/gnulib/manual/html_node/get_005fcurrent_005fdir_005fname.html ) I do not believe this function is available in all POSIX environments. It may be common in GNU runtime environments.

FYI: I just checked AIX and found the routine name "exists" in AIX <unistd.h>, but there is no documentation. So, it seems it may be visible on AIX, even if they have never taken the time to a is adding dd it to the getcwd() manual page.

Confusion #1 in adding this


.. versionadded:: 3.8


.. function:: lchflags(path, flags)

Set the flags of *path* to the numeric *flags*, like :func:`chflags`, but do
Expand Down
25 changes: 24 additions & 1 deletion Lib/os.py
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Expand Up @@ -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()
Expand Down Expand Up @@ -651,6 +651,29 @@ 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()

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I think empty lines in this functions are redundant. Empty lines inside functions are used for separating groups of statements in large functions, but this function is enough small and simple. And will be smaller after removing empty lines.

try:
pwd = environ["PWD"]
except KeyError:
return cwd

cwd_stat, pwd_stat = map(stat, [cwd, pwd])
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Would be clearer just to write two stat calls.


if (cwd_stat.st_dev == pwd_stat.st_dev and
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Maybe use samefile()?

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So, confusion #2 -, assuming that get_current_dir_name() is supported by the platform why is that not just being called rather than rewriting it? I admit my confusion comes from the lack of platform documentation, but why so hard? Wouldn't calling the "platform" implementation be more efficient than writing this in "pure" python.

More simply, why not use the platform implementation, perhaps adding it to posixmodule.c rather than here?

cwd_stat.st_ino == pwd_stat.st_ino):
return pwd
return cwd


# Change environ to automatically call putenv(), unsetenv if they exist.
from _collections_abc import MutableMapping

Expand Down
38 changes: 38 additions & 0 deletions Lib/test/test_os.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
import uuid
import warnings
from test import support
from unittest import mock

try:
import resource
Expand Down Expand Up @@ -1252,6 +1253,43 @@ 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(self.tmp_dir, os.getcwd())
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Swap arguments. The first argument is an actual value, the second argument is an expected value.

os.symlink(self.tmp_dir, self.tmp_lnk, True)
os.chdir(self.tmp_lnk)
self.assertEqual(self.tmp_dir, os.getcwd())
with mock.patch.dict('os.environ', {'PWD': self.tmp_dir}):
self.assertEqual(self.tmp_dir, os.getcwd())
with mock.patch.dict('os.environ', {'PWD': self.tmp_lnk}):
self.assertEqual(self.tmp_dir, os.getcwd())
os.unlink(self.tmp_lnk)
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The link will be leaked in the case of failure. It is better to use addCleanup(). Add the following line just before creating a link.

self.addCleanup(support.unlink, self.tmp_lnk)


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(self.tmp_dir, os.get_current_dir_name())
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(self.tmp_lnk, os.get_current_dir_name())
else:
self.assertEqual(self.tmp_dir, os.get_current_dir_name())
os.unlink(self.tmp_lnk)


class RemoveDirsTests(unittest.TestCase):
def setUp(self):
os.makedirs(support.TESTFN)
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-10-25-19-44-42.bpo-1154351.KhXLos.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Add get_current_dir_name() to the os module.
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