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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 load(self, modelfile, layer=None):
 """ Load or update a model or layers in a model. :param modelfile: The name of the json file to load. :type modelfile: str :param layer: Optionally load only specified layer. :type layer: str """

        # read modelfile, convert JSON and load/update model
        self.param_file = modelfile
        self._load(layer)
        self._update(layer)