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Python_Log_Level_Considerations.md

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Python Log Level Considerations

logging.basicConfig

In a Django application, consider whether or not the usage of logging.basicConfig will conflict with logging settings configured in the Django settings file. For example, if a module contains logging.basicConfig(level=logging.INFO) and a root logger is configured to log at DEBUG, what happens when the following is executed in the module: log.debug()? Is the log statement suppressed?

It's important to ensure that logging configuration can be modified via the settings file and not overridden by hard coded configuration.

Question

Do we really need to use this method at all in Django apps? If so, why?

Log levels

Ensure exceptions are logged using log.exception.

Logging errors at INFO level

Consider the following:

    try
        ...some code
    except Exception as error:
        log.info(error)

Here's an example of how an error looks when logged at INFO level:

INFO [2017-10-27 10:48:04,326] /abc/app/xyz/views.py [1533 140735838659520] list index out of range

This example has two problems:

  1. An error is logged at INFO level. Suppose a monitoring tool is checking log files by filtering on the log level, e.g. INFO, ERROR, etc. Also suppose it alerts on ERROR only. In this example the alert would never be triggered.
  2. It only logs the error message. It's critical to capture full stack traces and other relevant context when errors occur, not just messages.

Logging errors at ERROR level

The following example fixes these issues:

    try
        ...some code
    except Exception as error:
        log.exception(error)

Here's an example of the same error above, when logged at ERROR level, using log.exception:

ERROR [2017-10-27 10:58:38,933] /abc/app/xyz/views.py [1702 140735838659520] list index out of range 
Traceback (most recent call last):
  File "/abc/app/xyz/views.py", line 356, in some_function
    today = context['upcoming'][0].start
  File "/.virtualenvs/abc/lib/python2.7/site-packages/django/db/models/query.py", line 201, in __getitem__
    return list(qs)[0]
IndexError: list index out of range

Also, the python logging library contains two methods for logging errors: log.error() and log.exceptions(). Both log at ERROR level, however only one (exception method) will log a full stack trace.