code: def _attach_files(self, files_info):
          
  
          if not files_info.empty:
              if (len(files_info.index.unique()) != len(files_info)):
                  estr = 'WARNING! Duplicate datetimes in provided file '
                  estr = '{:s}information.\nKeeping one of each '.format(estr)
                  estr = '{:s}of the duplicates, dropping the rest.'.format(estr)
                  print(estr)
                  print(files_info.index.get_duplicates())
  
                  idx = np.unique(files_info.index, return_index=True)
                  files_info = files_info.ix[idx[1]]
                  #raise ValueError('List of files must have unique datetimes.')
  
              self.files = files_info.sort_index()
              date = files_info.index[0]
              self.start_date = pds.datetime(date.year, date.month, date.day)
              date = files_info.index[-1]
              self.stop_date = pds.datetime(date.year, date.month, date.day)
          else:
              self.start_date = None
              self.stop_date = None
              # convert to object type
              # necessary if Series is empty, enables == checks with strings
              self.files = files_info.astype(np.dtype('O'))
docs: Attaches info returned by instrument list_files routine to
          Instrument object.