Evaluate a postfix expression

In postfix notation the operator comes after its two operands: 3 4 + means 3 + 4, and 3 4 + 2 * means (3 + 4) * 2. It can be evaluated with a stack in one pass: read the tokens left to right; push every number; when you meet an operator, pop two numbers, apply the operator with the first-popped as the right-hand operand, and push the result. At the end the stack holds exactly one number, the answer.

Write evaluate(expression) for a space-separated expression using integers and the operators +, -, *. The expression is always valid.

evaluate("3 4 +")       ->  7
evaluate("3 4 + 2 *")   ->  14
evaluate("10 2 3 * -")  ->  4

def evaluate(expression):
    ...