code: def get_session_id(self):
          
          max_session = '0'
          try:
              with open(self.log_folder + os.sep + '_sessions.txt', 'r') as f:
                  for _ in f:
                      txt = f.readline()
                      if txt.strip('\n') != '':
                          max_session = txt
          except Exception:
              max_session = '1'
          
          this_session = str(int(max_session) + random.randint(9,100)).zfill(9) # not a great way to ensure uniqueness - TODO FIX  
          with open(self.log_folder + os.sep + '_sessions.txt', 'a') as f2:
              f2.write(this_session + '\n')
          return this_session
docs: get a unique id (shortish string) to allow simple aggregation
          of log records from multiple sources. This id is used for the 
          life of the running program to allow extraction from all logs.
          WARING - this can give duplicate sessions when 2 apps hit it 
          at the same time.