code: def write_molecule(filename, format=None):
      '''Write the system displayed in a file as a molecule.'''
      datafile(filename, format=format,
               mode='w').write('molecule',current_system()f write_molecule(filename, format=None):
      '''Write the system displayed in a file as a molecule.'''
      datafile(filename, format=format,
               mode='w').write('molecule',current_system())
docs: Write the system displayed in a file as a molecule.