Description

dfremont

opened on Feb 15, 2025

Issue body actions

Bug report

Bug description:

Prior to 3.13, the following code correctly raised a TypeError (I've tested 3.8-3.12, but see the last paragraph below):

def fun(x, /, **kwargs):
    pass

import inspect
sig = inspect.signature(fun)
sig.bind(x=1)

In 3.13, the binding succeeds even though the positional-only parameter was passed as a keyword argument (of course, fun(x=1) fails with a TypeError).

As far as I can tell this bug hasn't been previously reported, although issue #107831 reports inspect.getcallargs as having the same problem (prior to 3.13, unlike this bug).

I'm guessing the bug was introduced by #103404. If I try a version of 3.12 containing that patch (rather than the older versions I had installed previously), e.g. 3.12.9, it also exhibits the bug. It's possible that fixing the case where the positional-only parameter has a default value accidentally broke this case. Mentioning @jacobtylerwalls as the author of that PR in case they would like to take a look. Thanks!

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Linked PRs

• gh-130164: Fix inspect.Signature.bind() handling of positional-only args without defaults #130192
• [3.13] gh-130164: Fix inspect.Signature.bind() handling of positional-only args without defaults (GH-130192) #130271
• [3.12] gh-130164: Fix inspect.Signature.bind() handling of positional-only args without defaults (GH-130192) #132259

Reacted by Jacob Walls

Activity

1. dfremont

   added

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

   on Feb 15, 2025
2. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Feb 15, 2025
3. jacobtylerwalls commented on Feb 16, 2025

   

   jacobtylerwalls

   on Feb 16, 2025

   Contributor

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   Thanks, bisected to #103404 and testing a fix. Affects 3.12.4+
4. picnixz commented on Feb 16, 2025

   

   picnixz

   on Feb 16, 2025

   Member

   More actions

   Just to be clear, the issue is not that

   In 3.13, the binding succeeds even though the positional-only parameter was passed as a keyword argument

   Indeed, consider

   def fun(x, /, **kwargs): pass
   
   fun(1, x=2)

   So

   import inspect
   sig = inspect.signature(fun)
   sig.bind(x=1)

   means that you're binding it with a keyword argument x but it doesn't affect the positional-only parameter x itself. However, bind actually expects to specify all required arguments, in which case here the positional x is missing. So it's not because the positional-only parameter was passed as a keyword, it's more that we're actually thinking it was correctly specified.
5. picnixz

   added

   3.13only security fixesonly security fixes

   3.14bugs and security fixesbugs and security fixes

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

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   and removed

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

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Feb 16, 2025
6. picnixz commented on Feb 16, 2025

   

   picnixz

   on Feb 16, 2025

   Member

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   A fix for that could be to first check if we have a **kwargs in the signature. If we do, we need to first check if another argument should be bound before we fill the kwargs mapping. If a positional-only cannot be filled (for instance, x should first be checked as a non-keyword argument, if it's not possible to bind it, as in this case, we treat it as a kwarg), we store it as a keyword argument. Once we processed everything, we need to check if a positional-only is still missing because it wasn't treated in the first pass.

   EDIT: ok my paragraph is unclear but TL;DR we probably need a second pass to check that the arguments were properly bound (namely, a positional-only argument should only be bound from the *args of bind and not from anything **kwargs)
7. jacobtylerwalls

   added a commit that references this issue on Feb 16, 2025

   pythongh-130164: Fix inspect.signature.bind() handling of positional-…

   dd20797
8. serhiy-storchaka

   added a commit that references this issue on Feb 18, 2025

   gh-130164: Fix inspect.Signature.bind() handling of positional-only a…

   dab456d
9. serhiy-storchaka

   closed this as completedin #130192on Feb 18, 2025
10. miss-islington

    added a commit that references this issue on Feb 18, 2025

    pythongh-130164: Fix inspect.Signature.bind() handling of positional-…

    d6931c5
11. serhiy-storchaka commented on Feb 18, 2025

    

    serhiy-storchaka

    on Feb 18, 2025

    Member

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    Thank you for your report @dfremont and thank you for your quick fix @jacobtylerwalls.
12. serhiy-storchaka

    added a commit that references this issue on Apr 8, 2025

    [3.13] gh-130164: Fix inspect.Signature.bind() handling of positional…

    5c658c1
13. serhiy-storchaka

    added

    3.12only security fixesonly security fixes

    on Apr 8, 2025
14. miss-islington

    added a commit that references this issue on Apr 8, 2025

    pythongh-130164: Fix inspect.Signature.bind() handling of positional-…

    ecdf998
15. serhiy-storchaka

    added a commit that references this issue on Apr 8, 2025

    [3.12] gh-130164: Fix inspect.Signature.bind() handling of positional…

    40f81e1

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