when the input expression has been completely processedthe result is on the stack pop the operand_stack and return the value the complete function for the evaluation of postfix expressions is shown below to assist with the arithmetica helper function do_math is defined that will take two operands and an operator and then perform the proper arithmetic operation import stack as previously defined def postfix_eval(postfix_expr)operand_stack stack(token_list postfix_expr split(for token in token_listif token in " "operand_stack push(int(token)elseoperand operand_stack pop(operand operand_stack pop(result do_math(tokenoperand operand operand_stack push(resultreturn operand_stack pop(def do_math(opop op )if op ="*"return op op elif op ="/"return op op elif op ="+"return op op elsereturn op op print(postfix_eval(' /')it is important to note that in both the postfix conversion and the postfix evaluation programs we assumed that there were no errors in the input expression using these programs as starting pointyou can easily see how error detection and reporting can be included we leave this as an exercise at the end of the self check convert the following expression to postfix /( modify the infix_to_postfix function so that it can convert the following expression ^( the stack abstract data type