{"id":7632,"date":"2019-08-08T02:47:14","date_gmt":"2019-08-08T09:47:14","guid":{"rendered":"https:\/\/www.coretechnologies.com\/blog\/?p=7632"},"modified":"2023-07-26T16:33:47","modified_gmt":"2023-07-26T23:33:47","slug":"python-windows-service-output","status":"publish","type":"post","link":"https:\/\/www.coretechnologies.com\/blog\/alwaysup\/python-windows-service-output\/","title":{"rendered":"Q&A: How Do I See the Output\/Traceback From my Python Windows Service?"},"content":{"rendered":"
\"Q&A<\/div>\n
\n  We’re using AlwaysUp to run a Python program as a service<\/a>. Do you have any recommendations about logging?<\/p>\n

Ideally I would see the output of the python program as if it were run in command line, to see the traceback if there is an error. For example:<\/p>\n

\r\n    Traceback (most recent call last):\r\n    File \"\", line 1, in \r\n    NameError: name 'r' is not defined\r\n<\/pre>\n
— Liam<\/p>\n<\/div>\n
Hi Liam. I see your problem. It’s important to know when Python runs into a problem, but errors can be difficult to spot when the service’s console — alive and well in the isolated Session 0<\/a> — isn’t visible on your desktop.<\/p>\n
You have a couple of options:<\/p>\n
1. Capture the output of your Python program in a text file<\/h2>\n
AlwaysUp can capture Python’s command line output to a file of your choosing. That option is available on the Extras<\/b> tab:<\/p>\n
\"Capture<\/a><\/div>\n
Check the Capture output to this log file<\/b> box and enter the full path to a (new) text file.<\/p>\n
If your script generates lots of text, you may want to prevent the file from growing too large. Check the Automatically trim<\/b> box and specify the maximum size in megabytes. When the file grows to the maximum size, the oldest 10% will be discarded to make room for new entries. Be sure to tune the max size so that you don’t lose useful data.<\/p>\n
With those settings in place, your Python service will write all console\/traceback output to the file. Both the standard output<\/a> and standard error<\/a> streams will be captured.<\/p>\n
Open the file to see what’s going on with your script. Or even better, use the free Tail for Win32<\/a> to “track” the file. New lines will appear in real-time — just if you were looking at the Python console.<\/p>\n
To confirm our advice, we ran a Python script with a deliberate error (borrowed from this page<\/a>) and captured the output. Here is the result (with WinTail monitoring the output file):<\/p>\n
\"Python<\/a><\/div>\n
It works!<\/p>\n
2. Run your Python script in the current session, where you will see the console<\/h2>\n
If you don’t want to configure logging — or you just want to see the console temporarily while debugging a problem — you can instruct AlwaysUp to run the Python console on your desktop.<\/p>\n
Simply select Application > Restart in this session<\/b> and AlwaysUp will temporarily stop Python and “re-parent” it onto your screen:<\/p>\n
\"Restart<\/a><\/div>\n
Your program will run visibly while you are logged in. When you logout, AlwaysUp will automatically return your application to the background (i.e. Session 0).<\/p>\n
One final bit of advice…<\/h2>\n
We recommend that you do your best to thoroughly debug your Python script before<\/b> running it as a set-it-and-forget-it Windows Service. Dynamic languages like Python need extra attention in that area.<\/p>\n
The fewer surprises in production the better, right?<\/p>\n