pytype.abstract._singletons.Empty

An empty value. These values represent items extracted from empty containers. Because of false positives in flagging containers as empty (consider: x = [] def initialize(): populate(x) def f(): iterate(x) ), we treat these values as placeholders that we can do anything with, similar to Unsolvable, with the difference that they eventually convert to NothingType so that cases in which they are truly empty are discarded (see: x = ... # type: List[nothing] or Dict[int, str] y = [i for i in x] # The type of i is int; y is List[int] ). On the other hand, if Empty is the sole type candidate, we assume that the container was populated elsewhere: x = [] def initialize(): populate(x) def f(): return x[0] # Oops! The return type should be Any rather than nothing. The nothing -> anything conversion happens in convert.Converter._function_to_def and tracer_vm.CallTracer.pytd_for_types.