Logging¶
Extension for logging and registering errors.
In short, use the Flask application logger (current_app.logger
). Do
not create log files manually.
To run the examples below in a shell, be sure to first create the Flask application:
>>> from flask import current_app
>>> from invenio.base.factory import create_app
>>> app = create_app()
Logging errors¶
The preferred way to log errors is by using the Flask application logger:
>>> with app.app_context():
... try:
... raise Exception("This is an exception")
... except Exception:
... current_app.logger.exception("My message")
logger.exception()
will automatically include the exception stacktrace in
the log record, which each log handler may decide to include or not.
You may also manually include exception information in the logger using the
exc_info
keyword argument:
>>> import sys
>>> with app.app_context():
... try:
... raise Exception("This is an exception")
... except Exception:
... current_app.logger.critical("My message", exc_info=1)
Naturally, other log levels may also be used:
>>> app.logger.info("This is an info message")
>>> app.logger.warning("This is a warning message")
>>> app.logger.debug("This is a debug message")
Log handlers¶
Log messages written to the Flask application logger can be handled by many different backends, which is configurable by the an administrator. By default Invenio ships with following log handlers:
invenio.ext.logging.backends.fs
- Rotating file system handler.invenio.ext.logging.backends.legacy
- Error email reporting and logging to database. Default logging behaviour of Invenio 1.x.invenio.ext.logging.backends.sentry
- Logging to Sentry service (see https://pypi.python.org/pypi/sentry and https://getsentry.com/)
Installing one or more of the logging backends is a simple as including
them in your configuration variable EXTENSIONS
:
EXTENSIONS = [
# ...
'invenio.ext.logging',
'invenio.ext.logging.backends.fs',
'invenio.ext.logging.backends.legacy',
'invenio.ext.logging.backends.sentry',
# ...
]
Note that each backend may require additional configuration. Please see Backends for specific details.
Additionally if you plan to write your own backend, you may wish to consult Python’s logging documentation for how to create handlers, formatters and filters: https://docs.python.org/2/library/logging.html
Legacy handling of errors¶
Invenio 1.x used a method register_exception
to log errors. This method may
still be used, but may be deprecated in the future:
>>> from invenio.ext.logging import register_exception
>>> with app.app_context():
... try:
... raise Exception("This is an exception")
... except Exception as e:
... register_exception()
The method register_exception
is in fact just a small wrapper around the
application logger.
Error handling do’s and don’ts¶
Always use ``except Exception:`` (or preferably more specific exceptions)
over ``except:``, unless you explicitly want to catch the following built-in
exceptions (SystemExit
, KeyboardInterrupt
, GeneratorExit
).
See https://docs.python.org/2/library/exceptions.html#exception-hierarchy
Reraise. To gracefully handle errors, you may often catch
exceptions to perform some cleanup or e.g. convert a low-level library
exception into a more high-level application exception. This may however often
discard the initial exception and its traceback, making it hard to track
down the root cause. To preserve the traceback, simply reraise the caught
exception using a raise
with no arguments:
>>> with app.app_context():
... try:
... try:
... 0 / 0
... except ZeroDivisionError as e:
... # Do clean-up
... raise
... except Exception as e:
... current_app.logger.exception("Something bad happened")
If you like to convert the exception, it can be done like this:
>>> import six
>>> class AppError(Exception):
... pass
>>> with app.app_context():
... try:
... try:
... 0 / 0
... except ZeroDivisionError as e:
... six.reraise(MyAppError, "Custom message", sys.exc_info()[2])
... except AppError as e:
... current_app.logger.exception("Something bad happened")
Warnings¶
Warnings are useful to alert developers and system administrators about possible problems, e.g. usage of obsolete modules, deprecated APIs etc.
Please follow Invenio Deprecation policy section.
Backends¶
File system¶
Rotating file log handler for writing logs to the file system.
Configuration
LOGGING_FS_BACKUPCOUNT | Number of files to keep. Default: 5 . |
LOGGING_FS_MAXBYTES | Max file size in bytes. Default: 104857600
(100 MB). |
LOGGING_FS_LEVEL | Log level threshold for handler. Default:
WARNING . |
Sentry¶
Sentry logging backend.
Currently only Python application errors are sent to Sentry. Future extensions may allow for sending JavaScript errors to Sentry as well.
Configuration
SENTRY_DSN | Sentry DSN (get it from your Sentry account) . Required. |
LOGGING_SENTRY_LEVEL | Log level threshold for handler.
Default: WARNING . |
LOGGING_SENTRY_INCLUDE_WARNINGS | Include messages from warnings module.
Default: True . |
LOGGING_SENTRY_CELERY | Log Celery messages to Sentry.
Default: True . |
LOGGING_SENTRY_CELERY_TRANSPORT | Transport mechanism for Celery.
Default: sync . |
Raven (the Python library responsible for sending log messages to Sentry), supports some additionally configuration variables. See https://github.com/getsentry/raven-python/blob/master/raven/contrib/flask.py for further details.
Legacy¶
Invenio 1.x style error handling.
Logs exceptions to database and sends emails. Works only in connection with register_exception().
Configuration
LOGGING_LEGACY_LEVEL | Log level threshold for handler. Default:
ERROR . |