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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def PublishableBox(publishable, box_type, nodelist, model=None):
    "add some content type info of self.target"
    if not model:
        model = publishable.content_type.model_class()
    box_class = model.box_class

    if box_class == PublishableBox:
        box_class = Box
    return box_class(publishable, box_type, nodelist, model=model)