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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 model_fn(model_dir):
 """ Load the gluon model. Called once when hosting service starts. :param: model_dir The directory where model files are stored. :return: a model (in this case a Gluon network) """

    symbol = mx.sym.load('%s/model.json' % model_dir)
    outputs = mx.symbol.softmax(data=symbol, name='softmax_label')
    inputs = mx.sym.var('data')
    param_dict = gluon.ParameterDict('model_')
    net = gluon.SymbolBlock(outputs, inputs, param_dict)
    net.load_params('%s/model.params' % model_dir, ctx=mx.cpu())
    return net