docs: def init_tape(self, string):
          """Init system values."""
          for char in string:
              if char not in self.alphabet and not char.isspace() and char != self.EMPTY_SYMBOL:
                  raise RuntimeError('Invalid symbol: "' + char + '"')
  
          self.check()
          self.state = self.START_STATE
          self.head = 0
  
          self.tape = {}
          for i in range(len(string)):
              symbol = string[i] if not string[i].isspace() else self.EMPTY_SYMBOL
              self.tape[i] = symbol