input: Write a function to evaluate a given postfix expression and return the result. The function should take a string containing the postfix expression as input and return the evaluated value of the expression.
  
  def evaluate(expression):
  
      # split expression into list
      expression = expression.split()
  
      # stack to store integer values.
      stack = []
  
      # do for every element of expression.
      for element in expression:
  
          # If element is an operand push
          # into stack it's a number only
          if element.isdigit():
              stack.append(element)
  
          # if element is an operator,
          # pop two elements from stack
          # perform respective operations
          else:
              val1 = stack.pop()
              val2 = stack.pop()
              stack.append(str(eval(val2 + element + val1)))
  
      # return the value
      return (int(stack[0]))
  
  # Test cases
  assert evaluate("2 3 + 4 5 * *")==46
  assert evaluate("5 3 +")==8
  assert evaluate("10 3 5 * +")==25
  assert evaluate("2 3 + 4 *")==20
  assert evaluate("1 2 3 * +")==7
  assert evaluate("8 4 /")==2
  assert evaluate("9 3 %")==0
  assert evaluate("7 2 **")==49
  assert evaluate("3 4 + 2 * 7 /")==2
  assert evaluate("9 3 + 4 2 * +")==17
output: def evaluate(expression):
      expression = expression.split()
      stack = []
      for element in expression:
          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)
              elif element == '%':
                  stack.append(val2 % val1)
              elif element == '**':
                  stack.append(val2 ** val1)
      return stack[0]