Bound TypeVar on generic methods inside generic class











up vote
1
down vote

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For some reason, this code lints up as a problem:



from typing import *

T = TypeVar("T", bound="Foo")

S = TypeVar("S")



class Foo(Generic[S]):

    @classmethod

    def func(cls: Type[T]) -> T:

        return cls()


Mypy linter sends me to the def func line, saying Unsupported type Type["T"]. This does not happen if Foo is not defined as a generic class.



Is this a bug? What am I doing wrong?



I'm using S for different methods, and I wish to use T and Type[T] later on inside subclasses of Foo.






python-3.x generics typing type-variables







share|improve this question


























    up vote
    1
    down vote

    favorite












    For some reason, this code lints up as a problem:



    from typing import *
    
T = TypeVar("T", bound="Foo")
    
S = TypeVar("S")
    

    
class Foo(Generic[S]):
    
    @classmethod
    
    def func(cls: Type[T]) -> T:
    
        return cls()


    Mypy linter sends me to the def func line, saying Unsupported type Type["T"]. This does not happen if Foo is not defined as a generic class.



    Is this a bug? What am I doing wrong?



    I'm using S for different methods, and I wish to use T and Type[T] later on inside subclasses of Foo.






    python-3.x generics typing type-variables







    share|improve this question
























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      For some reason, this code lints up as a problem:



      from typing import *
      
T = TypeVar("T", bound="Foo")
      
S = TypeVar("S")
      

      
class Foo(Generic[S]):
      
    @classmethod
      
    def func(cls: Type[T]) -> T:
      
        return cls()


      Mypy linter sends me to the def func line, saying Unsupported type Type["T"]. This does not happen if Foo is not defined as a generic class.



      Is this a bug? What am I doing wrong?



      I'm using S for different methods, and I wish to use T and Type[T] later on inside subclasses of Foo.






      python-3.x generics typing type-variables







      share|improve this question













      For some reason, this code lints up as a problem:



      from typing import *
      
T = TypeVar("T", bound="Foo")
      
S = TypeVar("S")
      

      
class Foo(Generic[S]):
      
    @classmethod
      
    def func(cls: Type[T]) -> T:
      
        return cls()


      Mypy linter sends me to the def func line, saying Unsupported type Type["T"]. This does not happen if Foo is not defined as a generic class.



      Is this a bug? What am I doing wrong?



      I'm using S for different methods, and I wish to use T and Type[T] later on inside subclasses of Foo.






      python-3.x generics typing type-variables




      python-3.x generics typing type-variables






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Jun 26 at 12:01









      Bharel

      6,14411638




      6,14411638
























          1 Answer
          1






          active

          oldest

          votes

















          up vote
          2
          down vote



          accepted










          I believe this is a bug in mypy. Unfortunately, the best workaround for now is to just add a # type: ignore annotation to that line, perhaps along with a link to the relevant issue. Later, you can check if that warning has been fixed by running mypy with the --warn-unused-ignores flag.






          share|improve this answer





















          • Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
            – Bharel
            Jun 29 at 13:26










          • @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
            – Michael0x2a
            Jun 30 at 1:14










          • In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
            – Michael0x2a
            Jun 30 at 1:16










          • More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
            – Michael0x2a
            Jun 30 at 1:18










          • Thank you very much for the extended explanation! You're awesome!
            – Bharel
            Jun 30 at 8:43













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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          2
          down vote



          accepted










          I believe this is a bug in mypy. Unfortunately, the best workaround for now is to just add a # type: ignore annotation to that line, perhaps along with a link to the relevant issue. Later, you can check if that warning has been fixed by running mypy with the --warn-unused-ignores flag.






          share|improve this answer





















          • Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
            – Bharel
            Jun 29 at 13:26










          • @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
            – Michael0x2a
            Jun 30 at 1:14










          • In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
            – Michael0x2a
            Jun 30 at 1:16










          • More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
            – Michael0x2a
            Jun 30 at 1:18










          • Thank you very much for the extended explanation! You're awesome!
            – Bharel
            Jun 30 at 8:43

















          up vote
          2
          down vote



          accepted










          I believe this is a bug in mypy. Unfortunately, the best workaround for now is to just add a # type: ignore annotation to that line, perhaps along with a link to the relevant issue. Later, you can check if that warning has been fixed by running mypy with the --warn-unused-ignores flag.






          share|improve this answer





















          • Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
            – Bharel
            Jun 29 at 13:26










          • @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
            – Michael0x2a
            Jun 30 at 1:14










          • In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
            – Michael0x2a
            Jun 30 at 1:16










          • More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
            – Michael0x2a
            Jun 30 at 1:18










          • Thank you very much for the extended explanation! You're awesome!
            – Bharel
            Jun 30 at 8:43















          up vote
          2
          down vote



          accepted







          up vote
          2
          down vote



          accepted






          I believe this is a bug in mypy. Unfortunately, the best workaround for now is to just add a # type: ignore annotation to that line, perhaps along with a link to the relevant issue. Later, you can check if that warning has been fixed by running mypy with the --warn-unused-ignores flag.






          share|improve this answer












          I believe this is a bug in mypy. Unfortunately, the best workaround for now is to just add a # type: ignore annotation to that line, perhaps along with a link to the relevant issue. Later, you can check if that warning has been fixed by running mypy with the --warn-unused-ignores flag.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Jun 28 at 13:12









          Michael0x2a

          21.4k1671124




          21.4k1671124












          • Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
            – Bharel
            Jun 29 at 13:26










          • @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
            – Michael0x2a
            Jun 30 at 1:14










          • In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
            – Michael0x2a
            Jun 30 at 1:16










          • More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
            – Michael0x2a
            Jun 30 at 1:18










          • Thank you very much for the extended explanation! You're awesome!
            – Bharel
            Jun 30 at 8:43




















          • Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
            – Bharel
            Jun 29 at 13:26










          • @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
            – Michael0x2a
            Jun 30 at 1:14










          • In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
            – Michael0x2a
            Jun 30 at 1:16










          • More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
            – Michael0x2a
            Jun 30 at 1:18










          • Thank you very much for the extended explanation! You're awesome!
            – Bharel
            Jun 30 at 8:43


















          Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
          – Bharel
          Jun 29 at 13:26




          Apart from remembering all of mypy's issues, how do you find if things like this are a bug or not? Searching github isn't always easy for these issues.
          – Bharel
          Jun 29 at 13:26












          @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
          – Michael0x2a
          Jun 30 at 1:14




          @Bharel -- In general, mypy's type system is designed to be relatively straightforward. Of course, there are a few gotchas here and there, but if something feels like a bug, it usually is. (The second most common scenario is that you're looking for a feature that hasn't been implemented yet.)
          – Michael0x2a
          Jun 30 at 1:14












          In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
          – Michael0x2a
          Jun 30 at 1:16




          In this case, I read your snippet and agreed the error made no sense. I then found the relevant issue by searching "typevar classmethod" -- that narrowed down the number of issues to about. The reason I tacked on the keyword "classmethod" was because I happened to know that mypy currently struggles a little when working with decorators. You used a classmethod in your snippet, so I suspected that was likely partially the culprit. (If I were less lazy, I would have also tried repro-ing your issue after removing the @classmethod to confirm my hunch.)
          – Michael0x2a
          Jun 30 at 1:16












          More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
          – Michael0x2a
          Jun 30 at 1:18




          More broadly, you can try just asking on the gitter or filing an issue -- that's what I do when I'm not sure if something's a bug/if I can't find an open issue. Of course, sometimes I'm wrong and the code is fine/I missed the issue, but no biggie, mistakes happen. The mypy core devs encourage people to ask questions using the issue tracker anyways.
          – Michael0x2a
          Jun 30 at 1:18












          Thank you very much for the extended explanation! You're awesome!
          – Bharel
          Jun 30 at 8:43






          Thank you very much for the extended explanation! You're awesome!
          – Bharel
          Jun 30 at 8:43




















           

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