code: def pseudos_with_symbols(self, symbols):
          
          pseudos = self.select_symbols(symbols, ret_list=True)
          found_symbols = [p.symbol for p in pseudos]
          duplicated_elements = [s for s, o in collections.Counter(found_symbols).items() if o > 1]
  
          if duplicated_elements:
              raise ValueError("Found multiple occurrences of symbol(s) %s" % ', '.join(duplicated_elements))
          missing_symbols = [s for s in symbols if s not in found_symbols]
  
          if missing_symbols:
              raise ValueError("Missing data for symbol(s) %s" % ', '.join(missing_symbols))
  
          return pseudos
docs: Return the pseudos with the given chemical symbols.
  
          Raises:
              ValueError if one of the symbols is not found or multiple occurences are present.