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Title: Unusable type hint should not be silently ignored
Type: behavior Stage: resolved
Components: Versions: Python 3.9, Python 3.8, Python 3.7, Python 3.6
Status: closed Resolution: not a bug
Dependencies: Superseder:
Assigned To: Nosy List: aroberge, gvanrossum, levkivskyi
Priority: normal Keywords:

Created on 2020-08-05 14:25 by aroberge, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Messages (2)
msg374884 - (view) Author: Andre Roberge (aroberge) * Date: 2020-08-05 14:25
The following code is currently consistent with the type hint syntax but contains a line that is completely ignored.

   >>> d = {}
   >>> d['a']: int
   >>> d
   >>> __annotations__
    >>> '__annotations__' in dir(d)

I believe that type hints that cannot be either attached to an object nor added to any other __annotations__ dict should either generate a SyntaxError or, at the very least, result in a warning.
msg374889 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2020-08-05 15:03
No, that is up to the static type checker. With PEP 563 nearing completion in Python 3.10 we will in fact be ignoring all annotations silently.
Date User Action Args
2022-04-11 14:59:34adminsetgithub: 85660
2020-08-05 15:03:27gvanrossumsetstatus: open -> closed
resolution: not a bug
messages: + msg374889

stage: resolved
2020-08-05 14:53:46xtreaksetnosy: + gvanrossum, levkivskyi
2020-08-05 14:25:10arobergecreate