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
Init system values.