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self type on property creates a spurious error #3223

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JelleZijlstra opened this issue Apr 22, 2017 · 4 comments · Fixed by #4016
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self type on property creates a spurious error #3223

JelleZijlstra opened this issue Apr 22, 2017 · 4 comments · Fixed by #4016

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@JelleZijlstra
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Running mypy master on this file:

from typing import TypeVar, List
_T = TypeVar('_T')

class X:
    @property
    def __members__(self: _T) -> List[_T]: ...

reveal_type(X().__members__)

gives

../bin/selftypeproperty.py:8: error: Revealed type is 'builtins.list[selftypeproperty.X*]'
../bin/selftypeproperty.py:8: error: Invalid method type

The revealed type is correct but the "Invalid method type" doesn't make sense.
@JelleZijlstra JelleZijlstra mentioned this issue Apr 22, 2017
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@gvanrossum
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Is it the same if you rename __members__ to foo?

@JelleZijlstra
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Yes, doesn't make a difference.

@elazarg
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elazarg commented Apr 23, 2017

I should look into it.

Note that adding a bound, i.e. _T = TypeVar('_T', bound='X') seems to fix this.

@JelleZijlstra
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Thanks! FYI, the code where I found this had a Type over a bound typevar (python/typeshed#1195). It has _T = TypeVar('_T', bound=Enum) and the property is def __members__(self: Type[_T]) -> Mapping[str, _T]: ....

@elazarg elazarg mentioned this issue Apr 23, 2017
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@ilevkivskyi ilevkivskyi mentioned this issue Sep 4, 2017
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@elazarg elazarg mentioned this issue Sep 26, 2017
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elazarg added a commit to elazarg/mypy that referenced this issue Sep 26, 2017
@elazarg
Fix handling of non-method callable attribute (python#3223)
023219b 
1. Reverse subtyping check for self argument
2. For classmethod, fallback on the argument instead of on the parameter
3. Mimic dispatch better: meet original_type with static class
4. Better error message
@elazarg elazarg mentioned this issue Sep 26, 2017
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JukkaL pushed a commit that referenced this issue Oct 12, 2017
@elazarg @JukkaL
Fix checking of self when accessing a non-method callable attribute (…
bf9dc4c 
…take 2) (#4016)

Fix #3223. Minimal examples:

```
from typing import Callable
class X:
    f: Callable[[object], None]
X().f  # E: Invalid method type
```

```
class X:
    @Property
    def g(self: object): pass
X().g  # E: Invalid method type
```

The problem is that for non-methods the check performed on access 
to self is whether object <: X instead of the other way around.

1. Reverse subtyping check. This change alone fixes the issue described 
   above.
2. For classmethod, fall back on the argument instead of on the parameter.
3. Mimic dispatch better: meet original_type with static class. This handles 
   the case were instead of X() above there was something of type 
   Union[X, Y].
4. Better error message.

Take 2 of #3227, but without the reverse-operator part.
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@JelleZijlstra @gvanrossum @elazarg