code: def load_array(self, fn, name):
          
  
          if os.path.exists(fn + '.npz'):
              array = np.load(fn + '.npz')
              try:
                  setattr(self, name, array['arr_0'])
              except Exception, e:
                  print e
              finally:
                  array.close()
  
          else:
              raise RuntimeError("File %s does not exist." % (fn + '.npz'))
docs: Can only load files that were saved in the 'raw' format.
          Loads previously computed field 'name' from file
          Valid names are 'mag', 'direction', 'uca', 'twi'