it looks like you are saving a string as part of your model. See https://stackoverflow.com/questions/28218466/unpickling-a-python-2-object-with-python-3 312 for example.
Either dont save strings on your model, or instead of saving and loading the whole model, you can:
torch.save(filename, model.state_dict())

##
model = Model() # construct a new model
model.load_state_dict(torch.load(filename))

See https://github.com/pytorch/examples/tree/master/imagenet 145 for an example.