Mypy doesn't ensure self types are reasonable #2374

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1. ddfisher commented on Oct 28, 2016

   

   ddfisher

   on Oct 28, 2016

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   @elazarg
2. elazarg commented on Oct 29, 2016

   

   elazarg

   on Oct 29, 2016

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   Based on the above issue, this seems like a good idea... :)
3. JukkaL commented on Oct 31, 2016

   

   JukkaL

   on Oct 31, 2016

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   This looks like a dupe of #16, but I'll leave this open since there's a PR that references this.

   One thought from the discussion at #16: It may be reasonable to have a first argument (at least one not spelled as self) with an arbitrary annotation, but that function will not be a proper instance method and should only be callable within the class body. Example:

   class A:
       def f(x: str) -> int:   # ok
           return int(x)
   
       a = f('123')  # ok
   
   A().f()  # error, f is not a method
   

   #16 has more discussion.
4. gvanrossum commented on Oct 31, 2016

   

   gvanrossum

   on Oct 31, 2016 via email

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   Hm. Having fixed a bunch of issues the latest master found in both of our internal repos and typeshed, I would say that the fear of the pattern (functions without 'self' in classes) is exaggerated. The only thing we found was an interface (IMetadataProvider) in pkg_resources.py, which was meant for documentation only.
5. elazarg commented on Oct 31, 2016

   

   elazarg

   on Oct 31, 2016

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   IMO, ideally we would only allow use of such a function from within the class' scope. We would report an error for functions that are used from the outside (as suggested by Jukka), and also for functions that are unused from the inside.

   However, personally I would vote for requiring an explicit hint for such functions, keeping the policy and implementation simpler.
6. gvanrossum commented on Oct 31, 2016

   

   gvanrossum

   on Oct 31, 2016 via email

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   What would such an explicit hint look like?
7. elazarg commented on Nov 1, 2016

   

   elazarg

   on Nov 1, 2016

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   I was thinking about type: ignore... But of course it can be something else. And you can use @staticmethod I guess.
8. gvanrossum commented on Nov 1, 2016

   

   gvanrossum

   on Nov 1, 2016

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   Static methods can't be called without a class.

   >>> @staticmethod
   ... def f(): pass
   ...
   >>> f()
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: 'staticmethod' object is not callable
   >>>
   

   😕React with 😕1Reacted by Elazar Gershuni
9. gvanrossum

   closed this as completedin #2381on Nov 2, 2016
10. gvanrossum

    added a commit that references this issue on Nov 2, 2016

    Sanity checks for declared selftype (#2381)

    ...

    This issue will close once commit a90841f is merged into the 'master' branch.

    a90841f