Narrowing types to Literal using in syntax #12535
Description
Take this example code:
x = "a"
reveal_type(x)
assert x in ("a", "b", "c")
reveal_type(x)
y = 20
reveal_type(y)
assert y == 10 or y == 20 or y == 50
reveal_type(y)The current output of this is:
$ mypy x.py
x.py:2: note: Revealed type is "builtins.str"
x.py:4: note: Revealed type is "builtins.str"
x.py:7: note: Revealed type is "builtins.int"
x.py:9: note: Revealed type is "builtins.int"If mypy were to support type narrowing using chained or statements and in statements, the output would look like:
$ mypy x.py
x.py:4: note: Revealed type is "builtins.str"
x.py:6: note: Revealed type is "Union[Literal['a'], Literal['b'], Literal['c']]"
x.py:9: note: Revealed type is "builtins.int"
x.py:11: note: Revealed type is "Union[Literal[10], Literal[20], Literal[50]]"I think doing simple narrowing here would be relatively easy and very useful.