input: Write a function to evaluate a given 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_postfix(expression):
      elements = expression.split()
      stack = []
      for element in elements:
          if element.isdigit():
              stack.append(int(element))
          else:
              val1 = stack.pop()
              val2 = stack.pop()
              if element == '+':
                  stack.append(val2 + val1)
              elif element == '-':
                  stack.append(val2 - val1)
              elif element == '*':
                  stack.append(val2 * val1)
              elif element == '/':
                  stack.append(val2 // val1)
      return stack[0]
  assert evaluate_postfix("2 3 + 4 5 * *")==46
  assert evaluate_postfix("5 3 + 4 *")==32
  assert evaluate_postfix("10 2 * 5 +")==25
  assert evaluate_postfix("7 3 - 4 *")==16
  assert evaluate_postfix("8 4 / 2 *")==4
output: def evaluate_postfix(expression):
      elements = expression.split()
      stack = []
      for element in elements:
          if element.isdigit():
              stack.append(int(element))
          else:
              val1 = stack.pop()
              val2 = stack.pop()
              if element == '+':
                  stack.append(val2 + val1)
              elif element == '-':
                  stack.append(val2 - val1)
              elif element == '*':
                  stack.append(val2 * val1)
              elif element == '/':
                  stack.append(val2 // val1)
      return stack[0]