Signature.bind TypeErrors could be more helpful #83901

Activity

1. RazerM commented on Feb 21, 2020

   

   RazerMmannequin

   on Feb 21, 2020

   MannequinAuthor

   More actions

   Signature.bind does not tell you if a missing argument is keyword-only for example. I created the following snippet to examine the differences:

       import inspect
       
       def run(f):
           try:
               f()
           except TypeError as exc:
               print(exc.args[0])
           else:
               raise RuntimeError('Expected to raise!')
           sig = inspect.signature(f)
           try:
               sig.bind()
           except TypeError as exc:
               print(exc.args[0])
           else:
               raise RuntimeError('Expected to raise!')
           print()
       
       @run
       def f1(pos_only, /): ...
       
       @run
       def f2(pos_or_kw): ...
       
       @run
       def f3(*, kw_only): ...

   Output on current 3.9 master:

   f1() missing 1 required positional argument: 'pos_only'
   missing a required argument: 'pos_only'
   
   f2() missing 1 required positional argument: 'pos_or_kw'
   missing a required argument: 'pos_or_kw'
   
   f3() missing 1 required keyword-only argument: 'kw_only'
   missing a required argument: 'kw_only'
   

   I am willing to create a PR so that the TypeError for f3 says "missing a required keyword-only argument: 'kw_only'", if this would be accepted.
2. RazerM

   added

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

   type-featureA feature request or enhancementA feature request or enhancement

   on Feb 21, 2020
3. ezio-melotti

   transferred this issue fromon Apr 10, 2022
4. JelleZijlstra

   closed this as completedin f4f8133on Oct 7, 2022
5. carljm

   added a commit that references this issue on Oct 8, 2022

   Merge branch 'main' into typewatch

   ...

   27a4980
6. mpage

   added a commit that references this issue on Oct 11, 2022

   pythonGH-83901: Improve Signature.bind error message for missing keyw…

   ...

   c437b6e
7. serhiy-storchaka

   added a commit that references this issue on Aug 9, 2026

   pythonGH-83901: Improve Signature.bind error message for missing keyw…

   ...

   f4f8133