Recommender example is broken

[zjost]

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Description

Symbol used for enumeration in for loops is unintentionally overridden within the loop, which replaces the integer value with an mx.nd.array. This value is used in the return to scale the results, so it throws an exception.

Environment info (Required)

Ubuntu 16.01.

What to do:
1. Download the diagnosis script from https://raw.githubusercontent.com/apache/incubator-mxnet/master/tools/diagnose.py
2. Run the script using `python diagnose.py` and paste its output here.

Package used (Python/R/Scala/Julia):
Python

Steps to reproduce

Run the example.

What have you tried to solve it?

Submitted #14438

[mxnet-label-bot]

Hey, this is the MXNet Label Bot.
Thank you for submitting the issue! I will try and suggest some labels so that the appropriate MXNet community members can help resolve it.
Here are my recommended labels: Example