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None should be a subtype of an empty protocol #3906

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ilevkivskyi opened this issue Sep 1, 2017 · 4 comments
Closed

None should be a subtype of an empty protocol #3906

ilevkivskyi opened this issue Sep 1, 2017 · 4 comments
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@ilevkivskyi
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bug mypy got something wrong priority-2-low topic-protocols

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@ilevkivskyi
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Currently this gives an incompatible type error with --strict-optional, although it works with plain object:

class Empty(Protocol):
    pass

e: Empty
e = None  # Error

o: object
o = None # This is OK
@ilevkivskyi ilevkivskyi self-assigned this Sep 1, 2017
@ilevkivskyi ilevkivskyi added bug mypy got something wrong priority-2-low labels Sep 1, 2017
@gvanrossum
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Should we have a topic-protocols label?

@JukkaL
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JukkaL commented Sep 1, 2017

Yes. Do you want to add one?

@gvanrossum
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Created the label and added some issues. Ivan may want to double-check, there may be more issues to be categorized this way.

@ilevkivskyi
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Thanks! I added the label to few other issues.

@ilevkivskyi ilevkivskyi mentioned this issue Sep 24, 2017
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gvanrossum pushed a commit that referenced this issue Sep 29, 2017
@ilevkivskyi @gvanrossum
Minor updates to protocol semantics (#3996)
b3ca169 
This updates protocol semantic according to the discussion in python/typing#464:

    None should be considered a subtype of an empty protocol
    method = None rule should apply only to callable protocol members
    issublcass() is prohibited for protocols with non-method members.

Fixes #3906
Fixes #3938
Fixes #3939
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@JukkaL @gvanrossum @ilevkivskyi