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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 get_mnist_sym(output_op=None, num_hidden=400):
 """Get symbol of mnist"""

    net = mx.symbol.Variable('data')
    net = mx.symbol.FullyConnected(data=net, name='mnist_fc1', num_hidden=num_hidden)
    net = mx.symbol.Activation(data=net, name='mnist_relu1', act_type="relu")
    net = mx.symbol.FullyConnected(data=net, name='mnist_fc2', num_hidden=num_hidden)
    net = mx.symbol.Activation(data=net, name='mnist_relu2', act_type="relu")
    net = mx.symbol.FullyConnected(data=net, name='mnist_fc3', num_hidden=10)
    if output_op is None:
        net = mx.symbol.SoftmaxOutput(data=net, name='softmax')
    else:
        net = output_op(data=net, name='softmax')
    return net