为什么 exec() 或 os.system 在 pywin32 windows 服务中不起作用？

Question

### Run Python scripts as a service example (ryrobes.com)
### Usage : python aservice.py install (or / then start, stop, remove)

import win32service
import win32serviceutil
import win32api
import win32con
import win32event
import win32evtlogutil
import os, sys, string, time

class aservice(win32serviceutil.ServiceFramework):

    _svc_name_ = " Service"
    _svc_display_name_ = " Service"
    _svc_description_ = "Extract "
            
    def __init__(self, args):
            win32serviceutil.ServiceFramework.__init__(self, args)
            self.hWaitStop = win32event.CreateEvent(None, 0, 0, None)          

    def SvcStop(self):
            self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
            win32event.SetEvent(self.hWaitStop)                    
            
    def SvcDoRun(self):
        import servicemanager      
        servicemanager.LogMsg(servicemanager.EVENTLOG_INFORMATION_TYPE,servicemanager.PYS_SERVICE_STARTED,(self._svc_name_, ''))
        
        #self.timeout = 640000    #640 seconds / 10 minutes (value is in milliseconds)
        self.timeout = 10000     #120 seconds / 2 minutes
        # This is how long the service will wait to run / refresh itself (see script below)

        while 1:
            # Wait for service stop signal, if I timeout, loop again
            rc = win32event.WaitForSingleObject(self.hWaitStop, self.timeout)
            # Check to see if self.hWaitStop happened
            if rc == win32event.WAIT_OBJECT_0:
                # Stop signal encountered
                os.system("old_data.py")
                servicemanager.LogInfoMsg("Service - STOPPED!")  #For Event Log
                
                break

            else:

                    #Ok, here's the real money shot right here.
                    
                    #[actual service code between rests]
                try:
                    
                    os.system("old_data.py")
                    servicemanager.LogInfoMsg("OLD DATA UPDATED!")

                    #file_path = "C:\whereever\my_REAL_py_work_to_be_done.py"
                    exec(open("file.py").read())             #Execute the script
                    servicemanager.LogInfoMsg("Service - STARTED!")

                    #inc_file_path2 = "C:\whereever\MORE_REAL_py_work_to_be_done.py"
                    #exec(open(r"").read())        #Execute the script
                except:
                    pass
                #[actual service code between rests]