Type hints for __new__ no longer work when subclassing Dict #15135

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1. ShaneHarvey

   added

   bugmypy got something wrongmypy got something wrong

   on Apr 25, 2023
2. finite-state-machine commented on Aug 5, 2023

   

   finite-state-machine

   on Aug 5, 2023

   More actions

   This applies to (at least) FrozenSet as well.

   mypy-play.net: minimal reproduction case

   As motivation, consider [mypy-play.net]:

   from __future__ import annotations
   from typing import *
   
   class ModFrozenSet(FrozenSet[int]):
   
       some_str: str
   
       def __new__(cls, init: Iterable[int], some_str: str) -> ModFrozenSet:
           _ = some_str  # used by '__init__()'
           return frozenset.__new__(cls, init)
   
       def __init__(self, init: Iterable[int], some_str: str):
           _ = init  # used by '__new__()'
           self.some_str = some_str
   
   
   # Empirical test to show that this works in practice:
   
   def test_motivation_empirically() -> None:
   
       created = ModFrozenSet([1, 2, 3], "hello")
   
       assert type(created) is ModFrozenSet
       assert isinstance(created, frozenset)
       assert sorted(created) == [1, 2, 3]
       assert created.some_str == "hello"
3. finite-state-machine commented on Oct 30, 2023

   

   finite-state-machine

   on Oct 30, 2023

   More actions

   This appears to be fixed on the master branch, but not in 1.6.1 (per the first gist in my reply above).

   🎉React with 🎉1Reacted by Shane Harvey
4. ilevkivskyi

   closed this as completedon Nov 1, 2023