input: Write a function to evaluate a postfix expression. The input to the function should be a string with the postfix expression, and 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])) 
  
  # Test cases
  assert evaluate("2 3 + 4 5 * *") == 46
  assert evaluate("3 4 + 2 * 7 /") == 2
  assert evaluate("5 3 4 * +") == 17
  assert evaluate("10 20 +") == 30
  assert evaluate("100 5 2 * 25 - +") == 105
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]