Return the pseudo with the given chemical symbol.

        Args:
            symbols: String with the chemical symbol of the element
            allow_multi: By default, the method raises ValueError
                if multiple occurrences are found. Use allow_multi to prevent this.

        Raises:
            ValueError if symbol is not found or multiple occurences are present and not allow_multi

def pseudo_with_symbol(self, symbol, allow_multi=False):
        """
        Return the pseudo with the given chemical symbol.

        Args:
            symbols: String with the chemical symbol of the element
            allow_multi: By default, the method raises ValueError
                if multiple occurrences are found. Use allow_multi to prevent this.

        Raises:
            ValueError if symbol is not found or multiple occurences are present and not allow_multi
        """
        pseudos = self.select_symbols(symbol, ret_list=True)
        if not pseudos or (len(pseudos) > 1 and not allow_multi):
            raise ValueError("Found %d occurrences of symbol %s" % (len(pseudos), symbol))

        if not allow_multi:
            return pseudos[0]
        else:
            return pseudos