code: def pseudo_with_symbol(self, symbol, allow_multi=False):
          
          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
docs: 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