'Save the preprocessor list to a dict.'

def save(self, model):

    d = {'name': ''}
    preprocessors = []
    for i in range(model.rowCount()):
        item = model.item(i)
        pp_def = item.data(DescriptionRole)
        params = item.data(ParametersRole)
        preprocessors.append((pp_def.qualname, params))
    d['preprocessors'] = preprocessors
    return d
