Two questions about arrow operator ("->") in torch

the code i want to use has an arrow operator ("->") on their definition of the function
I understand what this operator meaning as the pre-specifiation of in/output variable type.
but i don’t know how to call this to refer/search the document. the first question is (1) what is the name of this operator or this rule?

and as my code described below, this function has different number of outputs depending on the name of the class. the error msg is
*** TypeError: dropout(): argument ‘input’ (position 1) must be Tensor, not tuple
i think the reason is pre-specifiation of the output as only “Tensor”. the second question is … (2) how can i fix it?

    def forward(self, inputs: Tensor, masks: Optional[Tensor] = None) -> Tensor:
        if self.module.__class__.__name__ is 'CLASSNAME_1':
            out_x, out_y  = self.module(inputs, masks) 
            return out_x, out_y 
            out = self.module(inputs)
            return out

I’m not sure about the exact name of the operator, but these are type annotations for the function that specify input and output types. The error is referring to the type of inputs, if it is a tuple then either the type annotation needs to be changed (seems unlikely) or the caller should make sure that inputs is indeed a Tensor.