Referencing function input variables from other input variables [duplicate]

I want to make some function like below:

def test_fn(var1: int = 1, var2: int = var1+1):     
    return var1, var2

(and the function above simply does not work which would raise NameError)

Is there any smart way of referencing var2 from var1 as input variable without adding or running other lines before this function?

Thanks in advance :D