constructing SGDsolver not from file

[Z.L]

In python to call caffe Solver, we could do 

solver = caffe.SGDSolver("solver.prototxt")

Since I would like to change one item of solver.prototxt each time, is there anyway I could directly construct solver? for example

solver = caffe.SGDSolver()

solver.net = "trian_val.prototxt"

If someone could help, that will be great!