[Python-Dev] Remaining decisions on PEP 471 -- os.scandir()

Ben Hoyt benhoyt at gmail.com
Tue Jul 15 14:19:35 CEST 2014

> I'd *keep DirEntry.lstat() method* regardless of existence of
> .stat(*, follow_symlinks=True) method (despite the slight violation of
> DRY principle) for readability. `dir_entry.lstat().st_mode` is more
> consice than `dir_entry.stat(follow_symlinks=False).st_mode` and the
> meaning of lstat is well-established -- get (symbolic link) status [2].

The meaning of lstat() is well-established, so I don't mind this. But
I don't think it's necessary, either. My thought would be that in new
code/functions we should kind of prescribe best-practices rather than
leave the options open. Yes, it's a few more characters, but
"follow_symlinks=True" is allow much clear than "l" to describe this
behaviour, especially for non-Linux hackers.

> I suggest *renaming .full_name -> .path* due to reasons outlined in [1].
> [1]: https://mail.python.org/pipermail/python-dev/2014-July/135441.html

Hmmm, perhaps. You suggest .full_name implies it's the absolute path,
which isn't true. I don't mind .path, but it kind of sounds like "the
Path object associated with this entry". I think "full_name" is fine
-- it's not "abs_name".

> follow_symlinks (if added) should be *keyword-only parameter* because
> `dir_entry.is_dir(False)` is unreadable (it is not clear at a glance
> what `False` means in this case).

Agreed follow_symlinks should be a keyword-only parameter (as it is in
os.stat() in Python 3).

> Exceptions are part of the public API. pathlib is inconsitent with
> os.path here e.g., os.path.isdir() ignores all OS errors raised by
> the stat() call but the corresponding pathlib call ignores only broken
> symlinks (non-existent entries).
> The cherry-picking of which stat errors to silence (implicitly) seems
> worse than either silencing the errors (like os.path.isdir does) or
> allowing them to propagate.

Hmmm, you're right there's a subtle difference here. I think the
os.path.isdir() behaviour could mask real errors, and the pathlib
behaviour is more correct. pathlib's behaviour is not implicit though
-- it's clearly documented in the docs:

> Returning False instead of raising OSError in is_dir() method simplifies
> the usage greatly without (much) negative consequences. It is a *rare*
> case when silencing errors could be more practical.

I think is_X() *should* fail if there are permissions errors or other
fatal errors. Whether or not they should fail if the file doesn't
exist (unlikely to happen anyway) or on a broken symlink is a
different question, but there's a good prececent with the existing
os/pathlib functions there.


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