Type torch::jit::Module converted to torch._C.ScriptModule

I’m trying to develop some torch.jit modules with c++,and then use them in python with pybind.
I found that the orginal method of torch._C.ScriptModule._create_method_from_trace
was created with arg types torch::jit::Module in c++. But the corresponding method arg type was torch._c.ScriptModule in python.
How dose this conversion happens?
I try to define a method in c++ with arg type torch::jit::Module. When exported to python, it’s arg type still torch::jit::Module.
What’s missed when building the program?