evaluate RPN expression

def evaluate(rpn_expression):
	intermediate_results = []
	DELIMITER = ','
	OPERATORS = {
	    '+':lambda y, x: x + y, '-': lambda y, x: x - y, '*':
	    lambda y, x: x * y. '/': lambda y, x: int(x / y)
	}

	for token in RPN_expression.split(DELIMETER):
		if token in OPERATORS:
			intermediate_results.append(OPERATORS[token](
				intermediate_results.pop(), intermediate_results.pop()))
		else: # token is a number.
            intermediate_results.append(int(token))
    return intermediate_results[-1]