Python logging SMTPHandler - handling offline SMTP server

Question

I have setup the logging module for my new python script. I have two handlers, one sending stuff to a file, and one for email alerts. The SMTPHandler is setup to mail anything at the ERROR level or above.

Everything works great, unless the SMTP connection fails. If the SMTP server does not respond or authentication fails (it requires SMTP auth), then the whole script dies.

I am fairly new to python, so I am trying to figure out how to capture the exception that the SMTPHandler is raising so that any problems sending the log message via email won't bring down my entire script. Since I am also writing errors to a log file, if the SMTP alert fails, I just want to keep going, not halt anything.

If I need a "try:" statement, would it go around the logging.handlers.SMTPHandler setup, or around the individual calls to my_logger.error()?

Answer 1

Exceptions which occur during logging should not stop your script, though they may cause a traceback to be printed to sys.stderr. In order to prevent this printout, do the following:

logging.raiseExceptions = 0

This is not the default (because in development you typically want to know about failures) but in production, raiseExceptions should not be set.

You should find that the SMTPHandler will attempt a re-connection the next time an ERROR (or higher) is logged.

logging does pass through SystemExit and KeyboardInterrupt exceptions, but all others should be handled so that they do not cause termination of an application which uses logging. If you find that this is not the case, please post specific details of the exceptions which are getting through and causing your script to terminate, and about your version of Python/operating system. Bear in mind that the script may appear to hang if there is a network timeout which is causing the handler to block (e.g. if a DNS lookup takes a long time, or if the SMTP connection takes a long time).

Answer 2

You probably need to do both. To figure this out, I suggest to install a local mail server and use that. This way, you can shut it down while your script runs and note down the error message.

To keep the code maintainable, you should extends SMTPHandler in such a way that you can handle the exceptions in a single place (instead of wrapping every logger call with try-except).