im2rec.py doesn't have docstrings. The online doc that describes the RecordIO format (here) doesn't describe how to use the script. Another page does, but it could really use a full-fledged real-world example, and should either be unified with or at least linked to from the other doc page.

In addition, the im2rec.py script encodes class labels as floating point numbers:

def write_list(path_out, image_list):
    with open(path_out, 'w') as fout:
        for i, item in enumerate(image_list):
            line = '%d\t' % item[0]
            for j in item[2:]:
                line += '%f\t' % j ### <---- THIS IS THE FLOATING POINT LABEL
            line += '%s\n' % item[1]
            fout.write(line)

But the doc page has integer labels in the example. When trying to make my own test .lst file by hand I used integer labels which in fact didn't work with mx.io.ImageRecordIter. It'd be great to get a clarification on the exact required .lst file format.