python - How to do calculations using text files and save the sum on the same text file -

i want calculations using text files , user input, want ask user number minus, want number text file used , minus number user gives , save sum in same text file original number was. problem don't know how this, example have number 13 on text file, user enters 4 sum 9, want 9 saved in same text file number 13 don't know how this. tried using file.write function no success.

i not quite sure how compare values of text file in if/else statement or while statements.

this have done far, apologize might not make sense, need work want work.

number = int(input('please enter number minus')) d = open("numberfile.txt","r+")            d.write(int(d.read()) - int(number))  d.close() 

whenever run says write argument must in str not int, when change str says operation - not supported.

you should open files with since handles outmatic file closing etc.

you should try if input of user , of input file convertable int.

import sys  input = input('please enter number minus\n') try:     number = int(input) except valueerror e:     print('error: ' + str(e))     print('input not integer, ' + str(type(input)))     sys.exit(1)  io_file = "numberfile.txt" open(io_file,"r") f:     input_from_file = f.read()  try:     number_from_file = int(input_from_file) except valueerror e:     print('error: ' + str(e))     print('input not integer, ' + str(type(input_from_file)))     sys.exit(1)  result = number_from_file - number open(io_file,"w") f:      f.write(str(result))