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Return type of dict.get is wrong when using strict optional checking #1732

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JukkaL opened this issue Jun 22, 2016 · 4 comments
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Return type of dict.get is wrong when using strict optional checking #1732

JukkaL opened this issue Jun 22, 2016 · 4 comments
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bug mypy got something wrong topic-strict-optional

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@JukkaL
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JukkaL commented Jun 22, 2016

The revealed type in the following program is int though it should be Optional[int] when using --strict-optional:

d = {'x': 1}
a = d.get('y')
reveal_type(a)

This also needs a typeshed change, but I think that there was a mypy issue with overloaded functions that is related. It's worth having a separate issue to track this here.
@JukkaL JukkaL added the bug mypy got something wrong label Jun 22, 2016
@gvanrossum
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I think this is relevant: python/typeshed#223 (comment)

@gvanrossum gvanrossum changed the title Return type of dict get wrong then using strict optional checking Return type of dict.get is wrong when using strict optional checking Jun 23, 2016
@ambv
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ambv commented Jan 12, 2017

Currently landed PR for this feature in typeshed: python/typeshed#822. Contains a Union[] return type so might have to be fixed to simple @overload.

@gvanrossum gvanrossum mentioned this issue May 11, 2017
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@ilevkivskyi
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It looks like this is fixed on master, I get:

Revealed type is 'Union[builtins.int*, builtins.None]'

@gvanrossum
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(Also, if you pass an explicit default of a different type, it becomes a union of int and that type, regardless of the --strict-optional setting. IIRC that was a problem in the past too.)

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@ambv @ddfisher @JukkaL @gvanrossum @ilevkivskyi