8000 Make join(None, T) produce Optional[T] in strict-optional by ddfisher · Pull Request #1999 · python/mypy · GitHub
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Make join(None, T) produce Optional[T] in strict-optional #1999

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Merged
merged 2 commits into from
Aug 8, 2016
Merged

Make join(None, T) produce Optional[T] in strict-optional #1999

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17acef1
Make join(None, T) produce Optional[T]
ddfisher Aug 8, 2016
93b57cf
remove extraneous blank line
ddfisher Aug 8, 2016
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Make join(None, T) produce Optional[T]
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@ddfisher
ddfisher committed Aug 8, 2016
commit 17acef12bcf155cd55559174345801d919ac3e10
10 changes: 9 additions & 1 deletion mypy/join.py
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Original file line number Diff line number Diff line change
Expand Up @@ -66,13 +66,17 @@ def join_types(s: Type, t: Type) -> Type:
if isinstance(s, ErasedType):
return t

if isinstance(s, UnionType) and not isinstance(t, UnionType):
s, t = t, s

if isinstance(s, NoneTyp) and not isinstance(t, NoneTyp):
s, t = t, s

# Use a visitor to handle non-trivial cases.
return t.accept(TypeJoinVisitor(s))



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You should never need three blank lines.

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Oops! That was accidental. As they say, "0.002K blank lines ought to be enough for anybody".

class TypeJoinVisitor(TypeVisitor[Type]):
"""Implementation of the least upper bound algorithm.

Expand Down Expand Up @@ -114,8 +118,12 @@ def visit_none_type(self, t: NoneTyp) -> Type:
if experiments.STRICT_OPTIONAL:
if isinstance(self.s, (NoneTyp, UninhabitedType)):
return t
elif isinstance(self.s, UnboundType):
return AnyType()
elif isinstance(self.s, Void) or isinstance(self.s, ErrorType):
return ErrorType()
else:
return self.default(self.s)
return UnionType.make_simplified_union([self.s, t])
else:
if not isinstance(self.s, Void):
return self.s
Expand Down
8 changes: 8 additions & 0 deletions test-data/unit/check-optional.test
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Expand Up @@ -330,3 +330,11 @@ def lookup_field(name, obj):
[out]
main: note: In function "lookup_field":
main:10: error: Need type annotation for variable

[case testTernaryWithNone]
reveal_type(None if bool() else 0) # E: Revealed type is 'Union[builtins.int, builtins.None]'
[builtins fixtures/bool.py]

[case testListWithNone]
reveal_type([0, None, 0]) # E: Revealed type is 'builtins.list[Union[builtins.int, builtins.None]]'
[builtins fixtures/list.py]
0