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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 mxnet_prefer_gpu():
 """If gpu available return gpu, else cpu Returns ------- context : Context The preferable GPU context. """

    gpu = int(os.environ.get('MXNET_GPU', default=0))
    if gpu in mx.test_utils.list_gpus():
        return mx.gpu(gpu)
    return mx.cpu()