infer dunder types

[KotlinIsland]

__str__ returns str
__repr__ returns str
__len__ returns int
__del__ returns None
__bool__ returns bool
__bytes__ returns bytes
__format__ returns str
__contains__ returns bool
__complex__ returns complex
__int__ returns int
__float__ returns float
__index__ returns int
__exit__: the three parameters are Optional[Type[BaseException]], Optional[BaseException], and Optional[TracebackType]
__aexit__: same as __exit__