def _make_default_operation_costs(self, allow_spaces=False):
        """
        sets 1.0 cost for every replacement, insertion, deletion and transposition
        """
        self.operation_costs = dict()
        self.operation_costs[""] = {c: 1.0 for c in list(self.alphabet) + [' ']}
        for a in self.alphabet:
            current_costs = {c: 1.0 for c in self.alphabet}
            current_costs[a] = 0.0
            current_costs[""] = 1.0
            if allow_spaces:
                current_costs[" "] = 1.0
            self.operation_costs[a] = current_costs
        # транспозиции
        for a, b in itertools.permutations(self.alphabet, 2):
            self.operation_costs[a + b] = {b + a: 1.0}
        # пробелы
        if allow_spaces:
            self.operation_costs[" "] = {c: 1.0 for c in self.alphabet}
            self.operation_costs[" "][""] = 1.0