An interactive book on deep learning. Much easy, so MXNet. Wow. [Straight Dope is growing up] ---> Much of this content has been incorporated into the new Dive into Deep Learning Book available at https://d2l.ai/.
Actually I would suggest author to remove most of the data_ctx in examples except maybe for one specific topic. It's a simple and straight concept but usually won't help a lot in simple/small-data examples.
I have been working through the gluon tutorials and found that in http://gluon.mxnet.io/chapter03_deep-neural-networks/mlp-gluon.html after the declaration of:
data_ctx = mx.cpu()
data_ctx is never actually used in the code. Unless I'm just being dense.