code: def load_file(cls, filepath):
          
          obj = cls()
          obj.system = obj._Input.load_file(filepath)
          obj.filename = os.path.basename(filepath)
          obj.system_id = obj.filename.split(".")[0]
          obj.name, ext = os.path.splitext(obj.filename)
          return obj
docs: Create a :class:`MolecularSystem` from an input file.
  
          Recognized input file formats: XYZ, PDB and MOL (V3000).
  
          Parameters
          ----------
          filepath : :class:`str`
             The input's filepath.
  
          Returns
          -------
          :class:`pywindow.molecular.MolecularSystem`
              :class:`MolecularSystem`