Description

assignee = None
closed_at = None
created_at = <Date 2020-02-21.22:41:33.023>
labels = ['type-feature', 'library']
title = 'Signature.bind TypeErrors could be more helpful'
updated_at = <Date 2020-02-21.22:41:33.023>
user = 'https://github.com/RazerM'

activity = <Date 2020-02-21.22:41:33.023>
actor = 'RazerM'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-02-21.22:41:33.023>
creator = 'RazerM'
dependencies = []
files = []
hgrepos = []
issue_num = 39720
keywords = []
message_count = 1.0
messages = ['362439']
nosy_count = 1.0
nosy_names = ['RazerM']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39720'
versions = []

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

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