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): 
    
      # 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])) 
  
  assert evaluate("2 3 + 4 5 * *") == 46
  assert evaluate("3 4 + 2 *") == 14
  assert evaluate("5 3 1 + *") == 20
  assert evaluate("8 2 / 4 *") == 16
  assert evaluate("9") == 9
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)
      return stack[0]