Attempting to parse specific keys in zoneinfo.ZoneInfo with tzdata installed will raise unhandled exceptions

e.g. on windows

>>> import zoneinfo
>>> zoneinfo.ZoneInfo('Pacific')
PermissionError: [Errno 13] Permission denied: 'C:\\Program Files\\Python39\\lib\\site-packages\\tzdata\\zoneinfo\\Pacific'

>>> import zoneinfo
>>> zoneinfo.ZoneInfo('__init__.py')
ValueError: Invalid TZif file: magic not found

This happens when non TZif files or directories in the tzdata.zoneinfo module are used as keys.

Hi. It seems like you are running Windows.

About the permission error, how did you install tzdata? Did you install it as an admin user and do you run Python as a different user?

tzdata was installed as an admin user, however this behaviour was
reproducible on a linux installation where for the ZoneInfo.('Pacific')
instance an IsADirectoryError would instead be raised.

On Wed, Aug 12, 2020 at 9:50 PM STINNER Victor <report@bugs.python.org>
wrote:

>
> STINNER Victor <vstinner@python.org> added the comment:
>
> Hi. It seems like you are running Windows.
>
> About the permission error, how did you install tzdata? Did you install it
> as an admin user and do you run Python as a different user?
>
> ----------
> nosy: +vstinner
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue41530>
> _______________________________________
>

Oh right, 'Pacific' is a directory, not a valid zone, and so ZoneInfoNotFoundError should be raised. I see.

Example:

$ ./python -m venv env
$ env/bin/python -m pip install tzdata
$ env/bin/python 

# ZoneInfoNotFoundError expected, get IsADirectoryError
>>> import zoneinfo; zoneinfo.ZoneInfo('Pacific')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/vstinner/python/master/Lib/zoneinfo/_common.py", line 12, in load_tzdata
    return importlib.resources.open_binary(package_name, resource_name)
  File "/home/vstinner/python/master/Lib/importlib/resources.py", line 40, in open_binary
    return reader.open_resource(resource)
  File "/home/vstinner/python/master/Lib/importlib/abc.py", line 419, in open_resource
    return self.files().joinpath(resource).open('rb')
  File "/home/vstinner/python/master/Lib/pathlib.py", line 1238, in open
    return io.open(self, mode, buffering, encoding, errors, newline,
IsADirectoryError: [Errno 21] Is a directory: '/home/vstinner/python/master/env/lib/python3.10/site-packages/tzdata/zoneinfo/Pacific'

# valid zone
>>> import zoneinfo; zoneinfo.ZoneInfo('Pacific/Noumea')
zoneinfo.ZoneInfo(key='Pacific/Noumea')

# raise ZoneInfoNotFoundError as expected (from FileNotFoundError)
>>> import zoneinfo; zoneinfo.ZoneInfo('xxx')
Traceback (most recent call last):
  File "/home/vstinner/python/master/Lib/zoneinfo/_common.py", line 12, in load_tzdata
    return importlib.resources.open_binary(package_name, resource_name)
  File "/home/vstinner/python/master/Lib/importlib/resources.py", line 40, in open_binary
    return reader.open_resource(resource)
  File "/home/vstinner/python/master/Lib/importlib/abc.py", line 419, in open_resource
    return self.files().joinpath(resource).open('rb')
  File "/home/vstinner/python/master/Lib/pathlib.py", line 1238, in open
    return io.open(self, mode, buffering, encoding, errors, newline,
  File "/home/vstinner/python/master/Lib/pathlib.py", line 1106, in _opener
    return self._accessor.open(self, flags, mode)
FileNotFoundError: [Errno 2] No such file or directory: '/home/vstinner/python/master/env/lib/python3.10/site-packages/tzdata/zoneinfo/xxx'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/vstinner/python/master/Lib/zoneinfo/_common.py", line 24, in load_tzdata
    raise ZoneInfoNotFoundError(f"No time zone found with key {key}")
zoneinfo._common.ZoneInfoNotFoundError: 'No time zone found with key xxx'

On Linux, converting IsADirectoryError to ZoneInfoNotFoundError is easy.

But on Windows, I don't think that converting any PermissionError into a ZoneInfoNotFoundError is a good idea. Maybe if PermissionError happens, we should check if the path is a directory.

Pseudo-code:

try:
  <open and read file>
except OSError as exc:
  if os.path.isdir(zone_path):
    raise ZoneInfoNotFoundError
  else:
    raise

Oh, I dislike Roundup UI. I didn't notice that a PR was submitted: PR 21839 (now closed).

I had opened a PR which just caught IsADirectoryError and PermissionError
but closed it as you'd mentioned that handling PermissionError that way
probably would not be the best, and I agree. I can reopen and modify to
check path on OSerror if you'd like otherwise feel free to handle however
you see fit.

I think that `ZoneInfo('__init__.py')` is also a problem, but a slightly different one. That comes from the fact that in order to support `importlib.resources`, each of the zoneinfo subdirectories needs an `__init__.py`, but the ZoneInfo constructor should probably ignore those, since they are added by `tzdata` and not actually part of a tzdata distribution.

By the way, it might be easiest to start with a PR against backports.zoneinfo, because I have a lot more linting, coverage and format checks set up there: https://github.com/pganssle/zoneinfo

I'll reopen the PR with an attempted resolution of the OSError related
issues however. In my quick testing it seems at least on Linux
backports.zoneinfo segfaults when trying `ZoneInfo('__init__.py')` so that
might be a larger issue for Paul to look into.