Narrowed down types sometimes not propagated to lambda #4297

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1. JukkaL

   added

   bugmypy got something wrongmypy got something wrong

   priority-1-normal

   topic-strict-optional

   on Nov 30, 2017
2. ikonst commented on Dec 31, 2018

   

   ikonst

   on Dec 31, 2018

   Contributor

   More actions

   Workaround:

   def g(b: Optional[str]) -> None:
       if b:
           _b = b  # https://github.com/python/mypy/issues/4297
           f1(lambda: _b.upper())

   👍React with 👍1Reacted by Peter Schutt
3. calimeroteknik commented on Sep 19, 2019

   

   calimeroteknik

   on Sep 19, 2019

   More actions

   This also seems to happen with native collection types whose size is "runtime" (i.e. recursive types in lambda-calculus terms), but not tuples (whose size is "fixed").

   Error / non-error cases added for reproduction, based on the original post:

   from typing import Optional, Callable
   
   def f1(key: Callable[[], str]) -> None: ...
   def f2(key: object) -> None: ...
   
   def g(b: Optional[str]) -> None:
       if b is not None:
           f1(lambda: b.upper())  # Item "None" of "Optional[str]" has no attribute "upper"
           z: Callable[[], str] = lambda: b.upper()  # Item "None" of "Optional[str]" has no attribute "upper"
           d = { "foo": lambda: b.upper() }  # Item "None" of "Optional[str]" has no attribute "upper"
           l = [ lambda: b.upper() ]  # Item "None" of "Optional[str]" has no attribute "upper"
           t = ( lambda: b.upper(), ) # No error
           f2(lambda: b.upper())  # No error
           lambda: b.upper()  # No error

   👍React with 👍1Reacted by herr kaste
4. JelleZijlstra

   added

   topic-type-narrowingConditional type narrowing / binderConditional type narrowing / binder

   on Mar 19, 2022
5. ilevkivskyi

   closed this as completedin #16407on Nov 4, 2023
6. ilevkivskyi

   added a commit that references this issue on Nov 4, 2023

   Fix type narrowing in lambda expressions (#16407)

   ...

   544e6ce
7. JukkaL

   added a commit that references this issue on Nov 10, 2023

   Fix type narrowing in lambda expressions (#16407)

   ...

   8813968