numpy dtype anomaly

[stullis]

According to the documentation, the usecols parameter does this:

usecols : int or sequence, optional

Which columns to read, with 0 being the first. For example, usecols = (1,4,5) will extract the 2nd, 5th and 6th columns. The default, None, results in all columns being read.

So, you're telling it to use column 0 and column 2 only but your dtype has four columns listed. Have you tried usecols with the same number of columns as the dtype?