docs: def channel_names(fn, usecols=None):
      """Return the field names (channel names) from dbf file fn. With
      usecols, return only names corresponding to the integers in
      usecols."""
  
      with open(fn, 'rb') as fo:
          names = dbfreader(fo).next()
  
      return usecols and [names[i] for i in usecols] or names