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Title: inspect.Parameter.__str__ does not include subscripted types in annotations
Type: behavior Stage: resolved
Components: Library (Lib) Versions: Python 3.11, Python 3.10, Python 3.9
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: andrei.avk, antonio-caceres, kj
Priority: normal Keywords:

Created on 2021-09-03 01:25 by antonio-caceres, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Messages (2)
msg400972 - (view) Author: Antonio Caceres (antonio-caceres) Date: 2021-09-03 01:25
The __str__ method of the inspect.Parameter class in the standard library's inspect module does not include subscripted types in annotations.

For example, consider the function foo(a: list[int]).
When I run str(inspect.signature(foo)), I would expect the returned string to be '(a: list[int])', but instead the string is '(a: list)'.

(I have tested this on Python 3.9.7, but the code I believe is the problem is on the branches for versions 3.9-3.11.) 

From a first glance at the source code, the problem is in the inspect.formatannotation function. If the annotation is a type, the formatannotation uses the __qualname__ attribute of the annotation instead of its __repr__ attribute. Indeed, list[int].__qualname__ == 'list' and repr(list[int]) == 'list[int]'. This problem was probably code that should have been changed, but never was, after PEP 585.

The only workarounds I have found is to implement an alternative string method that accepts inspect.Signature or subclass inspect.Parameter and override the __str__ method.
msg406132 - (view) Author: Andrei Kulakov (andrei.avk) * (Python triager) Date: 2021-11-10 20:55
I have confirmed and tested -- this was fixed in and so I'm closing it as fixed.
Date User Action Args
2022-04-11 14:59:49adminsetgithub: 89254
2021-11-10 20:55:42andrei.avksetstatus: open -> closed

nosy: + kj, andrei.avk
messages: + msg406132

resolution: fixed
stage: resolved
2021-09-03 01:25:32antonio-cacerescreate