Perhaps declare a __new__ instead of an __init__ for str and other similar types #4514

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1. srittau commented on Sep 6, 2020

   

   srittau

   on Sep 6, 2020

   Last edited by srittau

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   A short test indicates to me that str has both __init__() and __new__(), so we should define both in typeshed. (After checking with the implementation, of course.)

   Edit:

   Python 3.7.3 (default, Jul 25 2020, 13:03:44) 
   [GCC 8.3.0] on linux
   Type "help", "copyright", "credits" or "license" for more information.
   >>> str.__new__
   <built-in method __new__ of type object at 0x81ec40>
   >>> str.__init__
   <slot wrapper '__init__' of 'object' objects>
   >>> 

   👍React with 👍1Reacted by Yannick Duchêne
2. srittau

   added

   stubs: false positiveType checkers report false errorsType checkers report false errors

   on Sep 6, 2020
3. srittau commented on Sep 6, 2020

   

   srittau

   on Sep 6, 2020

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   @JelleZijlstra pointed to #1352 and #1464, where this was (unsuccessfully) tried before.
4. srittau commented on Sep 6, 2020

   

   srittau

   on Sep 6, 2020

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   FWIW, I just checked the following example from #1464:

   from enum import Enum
   from typing import TYPE_CHECKING
   
   if not TYPE_CHECKING:
       reveal_type = print
   
   class I(int, Enum):
       a = 1
   reveal_type(I['a'])  # E: Revealed type is '__main__.I'
   
   class S(str, Enum):
       a = '1'
   reveal_type(S['a'])  # E: Revealed type is '__main__.S'
   
   class F(float, Enum):
       a = 1.0
   reveal_type(F['a'])  # E: Revealed type is '__main__.F'

   It still works when I add the following definitions to str:

           @overload
           def __new__(cls: Type[_T], o: object = ...) -> _T: ...
           @overload
           def __new__(cls: Type[_T], o: bytes, encoding: str = ..., errors: str = ...) -> _T: ...

   (No guarantee that these are the correct definitions for str, though.) This makes me hopeful that the original underlying problem is solved.
5. srittau

   added a commit that references this issue on Sep 17, 2020

   Use __new__ instead of __init__ for some builtin classes

   ...

   This issue will close once commit 89b34c7 is merged into the 'main' branch.

   89b34c7
6. hauntsaninja

   closed this as completedin #4555on Sep 30, 2020
7. hauntsaninja

   added a commit that references this issue on Sep 30, 2020

   Use __new__ instead of __init__ for some builtin classes (#4555)

   ...

   This issue will close once commit 27dfbf6 is merged into the 'main' branch.

   27dfbf6