Reading in single str column with loadtxt
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I have the file called `mda_bk-adds-gro.inp`:

    # -*- mode:python -*-
    0.5, 0.5, 0.5, walp_fixed.gro
    0.5, 0.5, 0.4, walp.gro

I think I'll read the numbers and the the word separately. I've succeded in parsing the numbers:

    loadtxt('mda_bk-adds-gro.inp', comments='#', delimiter=',', usecols=(0,1,2))

But can't read in just words:

    loadtxt('mda_bk-adds-gro.inp', comments='#', delimiter=',', dtype=('fileName', '|S100'), usecols=(3))

but it gives an error:

     TypeError: 'int' object is not iterable

So my question is - how to I read the forth column with `loadtxt` provided the column is `str`?