The Function class inherits from with_metaclass(FunctionMeta, _C._FunctionBase, _ContextMethodMixin, _HookMixin) and it is really not clear whether the super class has an apply function.
Using pytorch 0.3.0
>>> from torch.autograd import Function
>>> Function.apply
<built-in method apply of FunctionMeta object at 0x55c10dfec7f8>