Django uses Python’s builtin logging module to perform system logging.
The usage of this module is discussed in detail in Python’s own documentation.
However, if you’ve never used Python’s logging framework (or even if you have),
here’s a quick primer.
A Python logging configuration consists of four parts:
A logger is the entry point into the logging system. Each logger is a named bucket to which messages can be written for processing.
A logger is configured to have a log level. This log level describes the severity of the messages that the logger will handle. Python defines the following log levels:
DEBUG: Low level system information for debugging purposesINFO: General system informationWARNING: Information describing a minor problem that has
occurred.ERROR: Information describing a major problem that has
occurred.CRITICAL: Information describing a critical problem that has
occurred.Each message that is written to the logger is a Log Record. Each log record also has a log level indicating the severity of that specific message. A log record can also contain useful metadata that describes the event that is being logged. This can include details such as a stack trace or an error code.
When a message is given to the logger, the log level of the message is compared to the log level of the logger. If the log level of the message meets or exceeds the log level of the logger itself, the message will undergo further processing. If it doesn’t, the message will be ignored.
Once a logger has determined that a message needs to be processed, it is passed to a Handler.
The handler is the engine that determines what happens to each message in a logger. It describes a particular logging behavior, such as writing a message to the screen, to a file, or to a network socket.
Like loggers, handlers also have a log level. If the log level of a log record doesn’t meet or exceed the level of the handler, the handler will ignore the message.
A logger can have multiple handlers, and each handler can have a
different log level. In this way, it is possible to provide different
forms of notification depending on the importance of a message. For
example, you could install one handler that forwards ERROR and
CRITICAL messages to a paging service, while a second handler
logs all messages (including ERROR and CRITICAL messages) to a
file for later analysis.
A filter is used to provide additional control over which log records are passed from logger to handler.
By default, any log message that meets log level requirements will be
handled. However, by installing a filter, you can place additional
criteria on the logging process. For example, you could install a
filter that only allows ERROR messages from a particular source to
be emitted.
Filters can also be used to modify the logging record prior to being
emitted. For example, you could write a filter that downgrades
ERROR log records to WARNING records if a particular set of
criteria are met.
Filters can be installed on loggers or on handlers; multiple filters can be used in a chain to perform multiple filtering actions.
Ultimately, a log record needs to be rendered as text. Formatters describe the exact format of that text. A formatter usually consists of a Python formatting string containing LogRecord attributes; however, you can also write custom formatters to implement specific formatting behavior.
Once you have configured your loggers, handlers, filters and formatters, you need to place logging calls into your code. Using the logging framework works like this:
# import the logging library
import logging
# Get an instance of a logger
logger = logging.getLogger(__name__)
def my_view(request, arg1, arg):
...
if bad_mojo:
# Log an error message
logger.error('Something went wrong!')
And that’s it! Every time the bad_mojo condition is activated, an
error log record will be written.
The call to logging.getLogger() obtains (creating, if
necessary) an instance of a logger. The logger instance is identified
by a name. This name is used to identify the logger for configuration
purposes.
By convention, the logger name is usually __name__, the name of
the Python module that contains the logger. This allows you to filter
and handle logging calls on a per-module basis. However, if you have
some other way of organizing your logging messages, you can provide
any dot-separated name to identify your logger:
# Get an instance of a specific named logger
logger = logging.getLogger('project.interesting.stuff')
The dotted paths of logger names define a hierarchy. The
project.interesting logger is considered to be a parent of the
project.interesting.stuff logger; the project logger
is a parent of the project.interesting logger.
Why is the hierarchy important? Well, because loggers can be set to
propagate their logging calls to their parents. In this way, you can
define a single set of handlers at the root of a logger tree, and
capture all logging calls in the subtree of loggers. A logging handler
defined in the project namespace will catch all logging messages
issued on the project.interesting and
project.interesting.stuff loggers.
This propagation can be controlled on a per-logger basis. If you don’t want a particular logger to propagate to its parents, you can turn off this behavior.
The logger instance contains an entry method for each of the default log levels:
logger.debug()logger.info()logger.warning()logger.error()logger.critical()There are two other logging calls available:
logger.log(): Manually emits a logging message with a
specific log level.logger.exception(): Creates an ERROR level logging
message wrapping the current exception stack frame.Of course, it isn’t enough to just put logging calls into your code. You also need to configure the loggers, handlers, filters and formatters to ensure that logging output is output in a useful way.
Python’s logging library provides several techniques to configure logging, ranging from a programmatic interface to configuration files. By default, Django uses the dictConfig format.
In order to configure logging, you use LOGGING to define a
dictionary of logging settings. These settings describes the loggers,
handlers, filters and formatters that you want in your logging setup,
and the log levels and other properties that you want those components
to have.
By default, the LOGGING setting is merged with Django’s
default logging configuration using the
following scheme.
If the disable_existing_loggers key in the LOGGING dictConfig is
set to True (which is the dictConfig default if the key is missing)
then all loggers from the default configuration will be disabled. Disabled
loggers are not the same as removed; the logger will still exist, but will
silently discard anything logged to it, not even propagating entries to a
parent logger. Thus you should be very careful using
'disable_existing_loggers': True; it’s probably not what you want. Instead,
you can set disable_existing_loggers to False and redefine some or all
of the default loggers; or you can set LOGGING_CONFIG to None
and handle logging config yourself.
Logging is configured as part of the general Django setup() function.
Therefore, you can be certain that loggers are always ready for use in your
project code.
The full documentation for dictConfig format is the best source of information about logging configuration dictionaries. However, to give you a taste of what is possible, here are several examples.
First, here’s a configuration which writes all logging from the django logger to a local file:
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'handlers': {
'file': {
'level': 'DEBUG',
'class': 'logging.FileHandler',
'filename': '/path/to/django/debug.log',
},
},
'loggers': {
'django': {
'handlers': ['file'],
'level': 'DEBUG',
'propagate': True,
},
},
}
If you use this example, be sure to change the 'filename' path to a
location that’s writable by the user that’s running the Django application.
Second, here’s an example of how to make the logging system print Django’s logging to the console. It may be useful during local development.
By default, this config only sends messages of level INFO or higher to the
console (same as Django’s default logging config, except that the default only
displays log records when DEBUG=True). Django does not log many such
messages. With this config, however, you can also set the environment variable
DJANGO_LOG_LEVEL=DEBUG to see all of Django’s debug logging which is very
verbose as it includes all database queries:
import os
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'handlers': {
'console': {
'class': 'logging.StreamHandler',
},
},
'loggers': {
'django': {
'handlers': ['console'],
'level': os.getenv('DJANGO_LOG_LEVEL', 'INFO'),
},
},
}
Finally, here’s an example of a fairly complex logging setup:
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'formatters': {
'verbose': {
'format': '{levelname} {asctime} {module} {process:d} {thread:d} {message}',
'style': '{',
},
'simple': {
'format': '{levelname} {message}',
'style': '{',
},
},
'filters': {
'special': {
'()': 'project.logging.SpecialFilter',
'foo': 'bar',
},
'require_debug_true': {
'()': 'django.utils.log.RequireDebugTrue',
},
},
'handlers': {
'console': {
'level': 'INFO',
'filters': ['require_debug_true'],
'class': 'logging.StreamHandler',
'formatter': 'simple'
},
'mail_admins': {
'level': 'ERROR',
'class': 'django.utils.log.AdminEmailHandler',
'filters': ['special']
}
},
'loggers': {
'django': {
'handlers': ['console'],
'propagate': True,
},
'django.request': {
'handlers': ['mail_admins'],
'level': 'ERROR',
'propagate': False,
},
'myproject.custom': {
'handlers': ['console', 'mail_admins'],
'level': 'INFO',
'filters': ['special']
}
}
}
This logging configuration does the following things:
Identifies the configuration as being in ‘dictConfig version 1’ format. At present, this is the only dictConfig format version.
Defines two formatters:
simple, that outputs the log level name (e.g., DEBUG) and the log
message.
The format string is a normal Python formatting string
describing the details that are to be output on each logging
line. The full list of detail that can be output can be
found in Formatter Objects.
verbose, that outputs the log level name, the log
message, plus the time, process, thread and module that
generate the log message.
Defines two filters:
project.logging.SpecialFilter, using the alias special. If this
filter required additional arguments, they can be provided as additional
keys in the filter configuration dictionary. In this case, the argument
foo will be given a value of bar when instantiating
SpecialFilter.django.utils.log.RequireDebugTrue, which passes on records when
DEBUG is True.Defines two handlers:
console, a StreamHandler, which prints any INFO
(or higher) message to sys.stderr. This handler uses the simple
output format.mail_admins, an AdminEmailHandler, which emails any ERROR
(or higher) message to the site ADMINS. This handler uses the
special filter.Configures three loggers:
django, which passes all messages to the console handler.django.request, which passes all ERROR messages to
the mail_admins handler. In addition, this logger is
marked to not propagate messages. This means that log
messages written to django.request will not be handled
by the django logger.myproject.custom, which passes all messages at INFO
or higher that also pass the special filter to two
handlers – the console, and mail_admins. This
means that all INFO level messages (or higher) will be
printed to the console; ERROR and CRITICAL
messages will also be output via email.If you don’t want to use Python’s dictConfig format to configure your logger, you can specify your own configuration scheme.
The LOGGING_CONFIG setting defines the callable that will
be used to configure Django’s loggers. By default, it points at
Python’s logging.config.dictConfig() function. However, if you want to
use a different configuration process, you can use any other callable
that takes a single argument. The contents of LOGGING will
be provided as the value of that argument when logging is configured.
If you don’t want to configure logging at all (or you want to manually
configure logging using your own approach), you can set
LOGGING_CONFIG to None. This will disable the
configuration process for Django’s default logging. Here’s an example that disables Django’s
logging configuration and then manually configures logging:
LOGGING_CONFIG = None
import logging.config
logging.config.dictConfig(...)
Setting LOGGING_CONFIG to None only means that the automatic
configuration process is disabled, not logging itself. If you disable the
configuration process, Django will still make logging calls, falling back to
whatever default logging behavior is defined.
Django provides a number of utilities to handle the unique requirements of logging in Web server environment.
Django provides several built-in loggers.
django¶The catch-all logger for messages in the django hierarchy. No messages are
posted using this name but instead using one of the loggers below.
django.request¶Log messages related to the handling of requests. 5XX responses are
raised as ERROR messages; 4XX responses are raised as WARNING
messages. Requests that are logged to the django.security logger aren’t
logged to django.request.
Messages to this logger have the following extra context:
status_code: The HTTP response code associated with the
request.request: The request object that generated the logging
message.django.server¶Log messages related to the handling of requests received by the server invoked
by the runserver command. HTTP 5XX responses are logged as ERROR
messages, 4XX responses are logged as WARNING messages, and everything else
is logged as INFO.
Messages to this logger have the following extra context:
status_code: The HTTP response code associated with the request.request: The request object that generated the logging message.django.template¶Log messages related to the rendering of templates.
DEBUG messages.django.db.backends¶Messages relating to the interaction of code with the database. For example,
every application-level SQL statement executed by a request is logged at the
DEBUG level to this logger.
Messages to this logger have the following extra context:
duration: The time taken to execute the SQL statement.sql: The SQL statement that was executed.params: The parameters that were used in the SQL call.For performance reasons, SQL logging is only enabled when
settings.DEBUG is set to True, regardless of the logging
level or handlers that are installed.
This logging does not include framework-level initialization (e.g.
SET TIMEZONE) or transaction management queries (e.g. BEGIN,
COMMIT, and ROLLBACK). Turn on query logging in your database if you
wish to view all database queries.
django.security.*¶The security loggers will receive messages on any occurrence of
SuspiciousOperation and other security-related
errors. There is a sub-logger for each subtype of security error, including all
SuspiciousOperations. The level of the log event depends on where the
exception is handled. Most occurrences are logged as a warning, while
any SuspiciousOperation that reaches the WSGI handler will be logged as an
error. For example, when an HTTP Host header is included in a request from
a client that does not match ALLOWED_HOSTS, Django will return a 400
response, and an error message will be logged to the
django.security.DisallowedHost logger.
These log events will reach the django logger by default, which mails error
events to admins when DEBUG=False. Requests resulting in a 400 response due
to a SuspiciousOperation will not be logged to the django.request
logger, but only to the django.security logger.
To silence a particular type of SuspiciousOperation, you can override that
specific logger following this example:
'handlers': {
'null': {
'class': 'logging.NullHandler',
},
},
'loggers': {
'django.security.DisallowedHost': {
'handlers': ['null'],
'propagate': False,
},
},
Other django.security loggers not based on SuspiciousOperation are:
django.security.csrf: For CSRF failures.django.db.backends.schema¶Logs the SQL queries that are executed during schema changes to the database by
the migrations framework. Note that it won’t log the
queries executed by RunPython.
Messages to this logger have params and sql in their extra context (but
unlike django.db.backends, not duration). The values have the same meaning
as explained in django.db.backends.
Django provides one log handler in addition to those provided by the Python logging module.
AdminEmailHandler(include_html=False, email_backend=None, reporter_class=None)¶This handler sends an email to the site ADMINS for each log
message it receives.
If the log record contains a request attribute, the full details
of the request will be included in the email. The email subject will
include the phrase “internal IP” if the client’s IP address is in the
INTERNAL_IPS setting; if not, it will include “EXTERNAL IP”.
If the log record contains stack trace information, that stack trace will be included in the email.
The include_html argument of AdminEmailHandler is used to
control whether the traceback email includes an HTML attachment
containing the full content of the debug Web page that would have been
produced if DEBUG were True. To set this value in your
configuration, include it in the handler definition for
django.utils.log.AdminEmailHandler, like this:
'handlers': {
'mail_admins': {
'level': 'ERROR',
'class': 'django.utils.log.AdminEmailHandler',
'include_html': True,
}
},
Note that this HTML version of the email contains a full traceback, with names and values of local variables at each level of the stack, plus the values of your Django settings. This information is potentially very sensitive, and you may not want to send it over email. Consider using something such as Sentry to get the best of both worlds – the rich information of full tracebacks plus the security of not sending the information over email. You may also explicitly designate certain sensitive information to be filtered out of error reports – learn more on Filtering error reports.
By setting the email_backend argument of AdminEmailHandler, the
email backend that is being used by the
handler can be overridden, like this:
'handlers': {
'mail_admins': {
'level': 'ERROR',
'class': 'django.utils.log.AdminEmailHandler',
'email_backend': 'django.core.mail.backends.filebased.EmailBackend',
}
},
By default, an instance of the email backend specified in
EMAIL_BACKEND will be used.
The reporter_class argument of AdminEmailHandler allows providing
an django.views.debug.ExceptionReporter subclass to customize the
traceback text sent in the email body. You provide a string import path to
the class you wish to use, like this:
'handlers': {
'mail_admins': {
'level': 'ERROR',
'class': 'django.utils.log.AdminEmailHandler',
'include_html': True,
'reporter_class': 'somepackage.error_reporter.CustomErrorReporter'
}
},
The reporter_class argument was added.
send_mail(subject, message, *args, **kwargs)¶Sends emails to admin users. To customize this behavior, you can
subclass the AdminEmailHandler class and
override this method.
Django provides some log filters in addition to those provided by the Python logging module.
CallbackFilter(callback)¶This filter accepts a callback function (which should accept a single argument, the record to be logged), and calls it for each record that passes through the filter. Handling of that record will not proceed if the callback returns False.
For instance, to filter out UnreadablePostError
(raised when a user cancels an upload) from the admin emails, you would
create a filter function:
from django.http import UnreadablePostError
def skip_unreadable_post(record):
if record.exc_info:
exc_type, exc_value = record.exc_info[:2]
if isinstance(exc_value, UnreadablePostError):
return False
return True
and then add it to your logging config:
'filters': {
'skip_unreadable_posts': {
'()': 'django.utils.log.CallbackFilter',
'callback': skip_unreadable_post,
}
},
'handlers': {
'mail_admins': {
'level': 'ERROR',
'filters': ['skip_unreadable_posts'],
'class': 'django.utils.log.AdminEmailHandler'
}
},
RequireDebugFalse¶This filter will only pass on records when settings.DEBUG is False.
This filter is used as follows in the default LOGGING
configuration to ensure that the AdminEmailHandler only sends
error emails to admins when DEBUG is False:
'filters': {
'require_debug_false': {
'()': 'django.utils.log.RequireDebugFalse',
}
},
'handlers': {
'mail_admins': {
'level': 'ERROR',
'filters': ['require_debug_false'],
'class': 'django.utils.log.AdminEmailHandler'
}
},
RequireDebugTrue¶This filter is similar to RequireDebugFalse, except that records are
passed only when DEBUG is True.
By default, Django configures the following logging:
When DEBUG is True:
django logger sends messages in the django hierarchy (except
django.server) at the INFO level or higher to the console.When DEBUG is False:
django logger sends messages in the django hierarchy (except
django.server) with ERROR or CRITICAL level to
AdminEmailHandler.Independent of the value of DEBUG:
INFO level
or higher to the console.All loggers except django.server propagate logging to their
parents, up to the root django logger. The console and mail_admins
handlers are attached to the root logger to provide the behavior described
above.
See also Configuring logging to learn how you can complement or replace this default logging configuration defined in django/utils/log.py.
Dec 20, 2019