Description

nineteendo

opened on Mar 29, 2024

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Bug report

Bug description:

>>> import ntpath
>>> ntpath.commonpath(["/foo", "foo"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<frozen ntpath>", line 808, in commonpath
ValueError: Can't mix absolute and relative paths

/foo is not an absolute path, but a rooted path, which can't be mixed with not-rooted paths.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-117381: Fix error message for ntpath.commonpath #117382

Activity

1. nineteendo

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Mar 29, 2024
2. aisk

   added

   OS-windows

   on Mar 30, 2024
3. aisk commented on Mar 30, 2024

   

   aisk

   on Mar 30, 2024

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   I did some googling and found that Microsoft has a document which describes "relative rooted path": https://learn.microsoft.com/en-us/dotnet/api/system.io.path.ispathrooted?view=net-8.0#remarks

   A relative rooted path specifies a drive, but its fully qualified path is resolved against the current directory.

   So I think the relative rooted path should be something like C:foo (please notice that it's not C:/foo), but /foo still is an absolute path. And ntpath.isabs('/foo') returns True, so I think it's an absolute path.
4. nineteendo commented on Mar 30, 2024

   

   nineteendo

   on Mar 30, 2024

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   ntpath.isabs('/foo') returns True

   That was recently changed:

   • GH-44626, GH-105476: Fix ntpath.isabs() handling of part-absolute paths #113829

   The error message could also be "Can't mix rooted and not-rooted paths" as /foo is rooted and foo is not.

   Reacted by An Long
5. zooba commented on Apr 2, 2024

   

   zooba

   on Apr 2, 2024

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   How does this change make life better or easier for those encountering this message?

   At first glance, it appears to be getting into overly precise terminology that doesn't help educate or correct the caller.
6. nineteendo commented on Apr 2, 2024

   

   nineteendo

   on Apr 2, 2024

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   The error message states: "Can't mix absolute and relative paths".
   But /foo & foo are both relative according to ntpath.isabs():

   Path	Rooted?	Absolute?
   c:/foo	Yes	Yes
   c:foo	Yes	No
   /foo	Yes	No
   foo	No	No

   So, this error message is factually incorrect.
   But /foo is rooted and foo is not, so that's what the new error message is in that case.
   On a side note, it could be useful to add os.path.isrooted.
7. serhiy-storchaka

   added a commit that references this issue on Apr 3, 2024

   gh-117381: Improve error messages for ntpath.commonpath() (GH-117382)

   2ec6bb4
8. serhiy-storchaka

   closed this as completedon Apr 3, 2024
9. diegorusso

   added a commit that references this issue on Apr 17, 2024

   pythongh-117381: Improve error messages for ntpath.commonpath() (pyth…

   6463fe5

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