The following code does not work on many OSX installations of Python via homebrew:

>> import webbrowser
>> webbrowser.open("http://www.google.com")

And throws the following error stack trace:

File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/webbrowser.py", line 26, in register
register_standard_browsers()
File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/webbrowser.py", line 551, in register_standard_browsers
raw_result = subprocess.check_output(cmd, stderr=subprocess.DEVNULL)
File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 411, in check_output
return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 489, in run
with Popen(*popenargs, **kwargs) as process:
File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 854, in __init__
self._execute_child(args, executable, preexec_fn, close_fds,
File "/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py", line 1702, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
NotADirectoryError: [Errno 20] Not a directory: 'xdg-settings'

The only workaround right now is to modify webbrowser.py via the instructions here: jupyter/notebook#3746 (comment).

Thank you for resolving.

It is far from clear what's going on here. In particular, it not clear to my why check_output(['xdg-settings', ...]) would ever raise NotADirectoryError.

• What packages do you have installed through homebrew?
• Is there an xdg-settings command installed on your system?
• Are DISPLAY or WAYLAND_DISPLAY in your shell environment?

That does seem very odd but the issue clearly has been seen by multiple users. Since it shouldn't cause any negative effects, I'm in favor of just adding NotADirectoryError to the try/except list as suggested in the workaround and make the problem go away.

I've created a PR that ignores this exception.

New changeset 23831a7 by Ronald Oussoren in branch 'master':
bpo-41754: Ignore NotADirectoryError in invocation of xdg-settings (GH-23075)
23831a7

New changeset 371c335 by Miss Islington (bot) in branch '3.9':
bpo-41754: Ignore NotADirectoryError in invocation of xdg-settings (GH-23075)
371c335

New changeset db087f6 by Miss Islington (bot) in branch '3.8':
bpo-41754: Ignore NotADirectoryError in invocation of xdg-settings (GH-23075) (GH-23198)
db087f6

Is it possible that your PATH contains a non-directory? Because it can give results a NotADirectoryError:

>>> subprocess.check_output(['xdg-settings', 'get', 'default-web-browser'], env={'PATH': '/etc/hosts'})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 429, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 510, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 962, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 1840, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
NotADirectoryError: [Errno 20] Not a directory: 'xdg-settings'

Reopened because I afraid that there may be a severe configuration error hidden by silencing NotADirectoryError.

Could you please show os.environ['PATH'] on your computer?

Is it possible that your PATH contains a non-directory? Because it can give results a NotADirectoryError:

>>> subprocess.check_output(['xdg-settings', 'get', 'default-web-browser'], env={'PATH': '/etc/hosts'})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 429, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 510, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 962, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/home/serhiy/py/cpython/Lib/subprocess.py", line 1840, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
NotADirectoryError: [Errno 20] Not a directory: 'xdg-settings'

Reopened because I afraid that there may be a severe configuration error hidden by silencing NotADirectoryError.

Could you please show os.environ['PATH'] on your computer?

Ignoring NotADirectoryError can ignore a configuration error, but this does match the behaviour of shells:

$ PATH=/etc/hosts ls                                                                                                             
zsh: command not found: ls

IMHO ignoring NotADirectory is the right thing to do here, there is no xdc-settings command found on the user's PATH even if that contains an invalid entry (not a directory or not existing). This avoids a strange error when the user has a directory on PATH that does not exist. One way this might happen is by having a shell profile that's shared between machines without having the same directory setup on all of them, I generally have the same PATH setting on all my test machines including $HOME/.local/bin but don't have that directory on all of them at all times.

I'm therefore reclining the issue.