Python win32 service

Question

Hey guys,

I am fairly new to python, and have no experience with writing services for windows. I have tried to hack together a windows service based on afew tutorials i have found out there.

I need this service to constantly monitor a directory for changes and when it sees a change it runs a script. Here is what i have so far:

import win32service
import win32serviceutil
import time

class aservice(win32serviceutil.ServiceFramework):
    _svc_name_ = "aservice"
    _svc_display_name_ = "aservice - It Does nothing"

    def __init__(self,args):
        win32serviceutil.ServiceFramework.__init__(self,args)
        self.isAlive = True

    def SvcDoRun(self):
        import servicemanager
        while self.isAlive:
            # This is where i am trying to run my code...is that right?
            self.main()
            #servicemanager.LogInfoMsg("aservice - is alive and well")
            #time.sleep(5)
            #servicemanager.LogInfoMsg("aservice - Stopped")

    def SvcStop(self):
        import servicemanager
        servicemanager.LogInfoMsg("aservice - Recieved stop signal")
        self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
        self.isAlive = False #this will make SvcDoRun() break the while loop at the next iteration.

    # This code monitors a directory for changes and calls a script when there is a change
    # At the moment, it creates a log file instead of calling the script
    def main(self):
        import os
        import win32file
        import win32con
        ACTIONS = {
            1: "Created",
            2: "Deleted",
            3: "Updated",
            4: "Renamed from something",
            5: "Ranamed to something"
        }

        FILE_LIST_DIRECTORY = 0x0001

        path_to_watch = "folder"
        hDir = win32file.CreateFile (
            path_to_watch,
            FILE_LIST_DIRECTORY,
            win32con.FILE_SHARE_READ | win32con.FILE_SHARE_WRITE,
            None,
            win32con.OPEN_EXISTING,
            win32con.FILE_FLAG_BACKUP_SEMANTICS,
            None
        )
        while 1:
            results = win32file.ReadDirectoryChangesW (
                hDir,
                1024,
                True,
                win32con.FILE_NOTIFY_CHANGE_FILE_NAME |
                win32con.FILE_NOTIFY_CHANGE_DIR_NAME |
                win32con.FILE_NOTIFY_CHANGE_ATTRIBUTES |
                win32con.FILE_NOTIFY_CHANGE_SIZE |
                win32con.FILE_NOTIFY_CHANGE_LAST_WRITE |
                win32con.FILE_NOTIFY_CHANGE_SECURITY,
                None,
                None
            )
            for action, file in results:
                #import script
                log = open ('log.txt', 'w')
                full_filename = os.path.join(path_to_watch)
                log.write(full_filename + ACTIONS.get(action, "Unknown"))
                log.close()

if __name__ == '__main__':
    win32serviceutil.HandleCommandLine(aservice)

Any ideas on what i am doing wrong?

EDIT: Here is the event log error i am getting for it.

Event Type: Error
Event Source:   aservice
Event Category: None
Event ID:   3
Date:       21/01/2010
Time:       11:27:43 AM
User:       N/A
Computer:
Description:
The instance's SvcRun() method failed 
Traceback (most recent call last):
  File "C:\Python25\Lib\site-packages\win32\lib\win32serviceutil.py", line 806, in SvcRun
    self.SvcDoRun()
  File "D:\TEST\simpleservice2.py", line 35, in SvcDoRun
    self.main()
  File "D:\TEST\simpleservice2.py", line 72, in main
    None
error: (2, 'CreateFile', 'The system cannot find the file specified.') 
%2: %3

Answer 1

I'm not familiar with pywin32's ServiceFramework, but based on your code and the error message, I bet you have a problem with path_to_watch.

I assume you sanitized the folder name for your example, and you're not actually looking for folder.

How about:

• Are you using the full path to the folder? The current working directory of the service may not be what you expect.
• Are you escaping any backslashes in the folder path?

Try using:

path_to_watch = r"c:\foo\bar\"

Answer 2

One thing to keep in mind with Windows services is that by default, they run under the LOCAL_SYSTEM account. This means that permissions to local volumes apply (LOCAL_SYSTEM can certainly be denied access to any given folder), and that LOCAL_SYSTEM does not have any access to any network volumes.