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PEP 702: More discussion of precedent and runtime behavior (#2946) 

Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>
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Jelle Zijlstra 2023-01-03 09:00:06 -08:00 committed by GitHub
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@ -85,6 +85,14 @@ Several users have requested support for such a feature:
* `Pyright feature request <https://github.com/microsoft/pyright/discussions/2300>`__ * `Pyright feature request <https://github.com/microsoft/pyright/discussions/2300>`__
* `mypy feature request <https://github.com/python/mypy/issues/11439>`__ * `mypy feature request <https://github.com/python/mypy/issues/11439>`__
There are similar existing third-party tools:
* `Deprecated <https://pypi.org/project/Deprecated/>`__ provides a decorator to
mark classes, functions, or methods as deprecated. Access to decorated objects
raises a runtime warning, but is not detected by type checkers.
* `flake8-deprecated <https://pypi.org/project/flake8-deprecated/>`__ is a linter
plugin that warns about use of deprecated features. However, it is limited to
a short, hard-coded list of deprecations.
Specification Specification
============= =============
@ -157,8 +165,8 @@ Here is how type checkers should handle usage of this library:
import library import library
library.norwegian_gray(1) # error: Use of deprecated function norwegian_gray. It is pining for the fiords. library.norwegian_blue(1) # error: Use of deprecated function norwegian_blue. It is pining for the fiords.
map(library.norwegian_gray, [1, 2, 3]) # error: Use of deprecated function norwegian_gray. It is pining for the fiords. map(library.norwegian_blue, [1, 2, 3]) # error: Use of deprecated function norwegian_blue. It is pining for the fiords.
library.foo(1) # error: Use of deprecated overload for foo. Only str will be allowed. library.foo(1) # error: Use of deprecated overload for foo. Only str will be allowed.
library.foo("x") # no error library.foo("x") # no error
@ -236,9 +244,11 @@ Users might expect usage of the ``@deprecated`` decorator to issue a
thorny issues: thorny issues:
* When the decorator is applied to a class or an overload, the warning * When the decorator is applied to a class or an overload, the warning
would not be raised as expected. would not be raised as expected. For classes, the warning could be
* Users may want to control the ``warn`` call in more detail (e.g., raised on instantiation, but this would not cover usage in type
changing the warning class). annotations or :func:`isinstance` checks.
* Users may want to control the :func:`~warnings.warn` call in more detail
(e.g., changing the warning class).
* ``typing.py`` generally aims to avoid affecting runtime behavior. * ``typing.py`` generally aims to avoid affecting runtime behavior.
Users who want to use ``@deprecated`` while also issuing a runtime warning Users who want to use ``@deprecated`` while also issuing a runtime warning