code: def from_csv(cls, path):
          
          with open(path) as f:
              fields = map(float, next(f).split(','))
          if len(fields) == 3:
              return u.Quantity([[fields[0], 0, 0],
                                 [0, fields[1], 0],
                                 [0, 0, fields[2]]], unit=u.nanometers)
          elif len(fields) == 9:
              return u.Quantity([fields[0:3],
                                 fields[3:6],
                                 fields[6:9]], unit=u.nanometers)
          else:
              raise ValueError('This type of CSV is not supported. Please '
                               'provide a comma-separated list of three or nine '
                               'floats in a single-line file.')
docs: Get box vectors from comma-separated values in file `path`.
  
          The csv file must containt only one line, which in turn can contain
          three values (orthogonal vectors) or nine values (triclinic box).
  
          The values should be in nanometers.
  
          Parameters
          ----------
          path : str
              Path to CSV file
  
          Returns
          -------
          vectors : simtk.unit.Quantity([3, 3], unit=nanometers