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Conditional expression with branches of type None and T should be Optional[T], not object #1820
Description
Consider:
def f(flag; bool) -> Optional[int]:
a = (None if flag else 0)
return aWhen run with --strict-optional I get the error
error: Incompatible return value type (got "object", expected "Optional[int]")
It looks like the unification code is not understanding what's going on and falling back on object.
Activity
ddfisher commentedon Jul 21, 2016
Related to #1863. This is due to mypy's reluctance to make Union types.
gnprice commentedon Aug 1, 2016
As discussed under #1863, we should go ahead and become willing to make Union types when one of the types to be combined is None. We might go back later and become less reluctant to make Union types more broadly, but there's more detailed discussion to be had there (see #1863.)
Make join(None, T) produce Optional[T] in strict-optional (#1999)