input: Write a function to evaluate a postfix expression. The input to the function should be a string with the postfix expression. The output should be the evaluated value of the expression.
  def evaluate(expression): 
      expression = expression.split() 
      stack = []  
      for element in expression: 
          if element.isdigit(): 
              stack.append(element) 
          else:  
              val1 = stack.pop() 
              val2 = stack.pop() 
              stack.append(str(eval(val2 + element + val1))) 
      return (int(stack[0]))
  assert evaluate("2 3 + 4 5 * *")==46
output: def evaluate(expression): 
      expression = expression.split() 
      stack = []  
      for element in expression: 
          if element.isdigit(): 
              stack.append(element) 
          else:  
              val1 = stack.pop() 
              val2 = stack.pop() 
              stack.append(str(eval(val2 + element + val1))) 
      return (int(stack[0]))