TypedDict and NamedTuple do not evaluate cross-module ForwardRef in all cases #90531

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1. aha79 commented on Jan 14, 2022

   

   aha79mannequin

   on Jan 14, 2022

   MannequinAuthor

   More actions

   TypedDict does not resolve cross-module ForwardRefs when the ForwardRef is not a direct one.

   In other words the fix #71204 (bpo-41249) for TypedDict seems incomplete.

   The same issue seem to exist for NamedTuple.

   Example:

      #module.py
      TD = typing.TypedDict("TD", {'test': typing.List[typing.Optional['Y']]})
      class Y:
         pass
   
   
      # other module
      class TDSub(module.TD):
          a: int
      get_type_hints(TDSub)
      # -> Exception   NameError: Y not found

   On the other hand, with direct ForwardRef, as e.g. in
   TD = typing.TypedDict("TD", {'test': 'Y' } )

   it works (that was indeed fixed by #71204)

   Same issue exists for NamedTuple. There neither of the above works, i.e. cross-module ForwardRefs are never resolve (but they could - als NamedTuple has the __module__ member set with to calling module). I am not sure if inheritance for NamedTuple is supported so I do not know if it is really a bug.

   The problem in the code is that in TypedDict the module parameter is passed only onto the immediate ForwardRef. One option could be to recursively walk the type and search for unpatched ForwardRefs and set the module parameter.
   On the other hand, the retroactive patching of forward refs is problematic as it may mess with the caching mechanism im typing.py. There may be a type with ForwardRef already in cache (and used by more than one user), but only for one user the module is to be updated. So probably a correct implementation is tricky, or some other way has to be found to update the module of ForwardRefs (e.g. by copying the type tree).

   For NamedTuple the whole mechanism of passing the module parameter to the ForwardRefs is not done (not even for direct ForwardRef ones).

   Not sure how important this (likely not very) is as I do not use TypedDict and NamedTuple. This is just to report it.
2. aha79

   added

   3.10 (EOL)end of lifeend of life

   3.11only security fixesonly security fixes

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Jan 14, 2022
3. ezio-melotti

   transferred this issue fromon Apr 10, 2022
4. AlexWaygood

   added

   topic-typing

   on Apr 13, 2022