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Improve type inference for "Optional[T] or T" expression #1817

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gvanrossum opened this issue Jul 7, 2016 · 1 comment · Fixed by #1828
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Improve type inference for "Optional[T] or T" expression #1817

gvanrossum opened this issue Jul 7, 2016 · 1 comment · Fixed by #1828
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gvanrossum commented Jul 7, 2016 •
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Consider this:

def f(a: Optional[str]) -> str:
    return a or 'default'

This should type-check under --strict-optional, but currently the type of a or 'default' is inferred as Optional[str]. It should realize that if a is None the right branch is always taken.
@gvanrossum gvanrossum changed the title Improve type inference for Optional[x] Improve type inference for "Optional[T] or T" expression Jul 7, 2016
@gvanrossum gvanrossum self-assigned this Jul 7, 2016
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JukkaL commented Jul 7, 2016

Dupe of #1733?

gvanrossum pushed a commit that referenced this issue Jul 7, 2016
For Optional[T] or T, infer the type T instead of Optional[T].
80056c6 
Fixes #1817.
@gvanrossum gvanrossum mentioned this issue Jul 7, 2016
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gvanrossum pushed a commit that referenced this issue Jul 7, 2016
For Optional[T] or T, infer the type T instead of Optional[T].
690c4d5 
Fixes #1817, fixes #1733.
@ddfisher ddfisher mentioned this issue Jul 8, 2016
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gvanrossum pushed a commit that referenced this issue Jul 8, 2016
@ddfisher @gvanrossum
Use information from find_isinstance_check typing boolean operators (#…
4c11bb3 
…1828)

Fixes #1817, fixes #1733.
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