def indices_from_symbol(self, symbol: str) -> tuple:
        """
        Returns a tuple with the sequential indices of the sites
        that contain an element with the given chemical symbol.
        """
        return tuple((i for i, specie in enumerate(self.species)
                      if specie.symbol == symbol))
def indices_from_symbol ( self , symbol : str ) -> tuple : return tuple ( ( i for i , specie in enumerate ( self . species ) if specie . symbol == symbol ) )
Returns a tuple with the sequential indices of the sites
        that contain an element with the given chemical symbol.