Implement sentinels as types, support isinstance and match statments #715
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The `repr` parameters position was replaced by `module_name` to conform to PEP 661. Added copy and pickle tests. Updated documentation for Sentinel. `_marker` was defined before `caller` which causes minor issues, resolved by setting its module name manually.
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## main #715 +/- ##
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Adds support for isinstance and match statements Methods required to make sentinels pretend they are types are no longer necessary `self._name` replaced with `self.__name__` Updated tests and documentation
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This should be in PEP 661 first before we guarantee support for additional behaviors in typing-extensions. |
I guess I got ahead of myself following the PEP 661 discussions. The only additional behavior here is Does this apply to #617 too? Because I thought that was following the specification after I removed all the extraneous changes in the latest push, but I never received feedback on that which is why I made a separate PR for this one because I couldn't tell if anything was wrong with #617 or if simply nobody was free to look at it at the time. |
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If we implement sentinels as classes, users will surely start relying on this fact. I don't think we should do that unless and until PEP 661 calls for it. Unfortunately PEP 661 stalled out again... I wrote to Tal a few months ago offering to help push it to completion, but he thought he'd be able to work on it. Maybe I should reach out to him again, but I'm more busy again now too. |
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Two main things here:
typefunction to dynamically generate new sentinel types._SentinelMetais setup so that sentinels can be used with themselves inisinstancechecks.This new type logic ended up being simpler than the workarounds required to make sentinels pretend they are types so I ended up removing those workarounds. I'm not fully experienced with their usage but they were covered by tests.
This PR is based on #617 so
reprbeing made a keyword parameter is included. With sentinels being types now it's more important to get__module__correct anyways. Pickle is supported and tested.self.__name__takes the place ofself._namenow that sentinels are types.Updated documentation for sentinels, in addition to #617 it now explains
isinstanceandmatchstatements.Improved the error message for calling a sentinel to include the name of the sentinel.
isinstance(MySentinel, typing_extensions.Sentinel)currently returnsFalse, but that can be changed in__instancecheck__if necessary.Relevant documentation:
__instancecheck__typefunctionCloses #720