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Django2.0手册 AI君 124℃

A quick logging primer¶

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.

The cast of players

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 purposes
  • INFO: General system information
  • WARNING: Information describing a minor problem that has
  • ERROR: Information describing a major problem that has
  • CRITICAL: Information describing a critical problem that has

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.

Using logging¶

Once you have configured your loggers, handlers, filters and
formatters, you need to place logging calls into your code. Using the
logging framework is very simple. Here’s an example:

# 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.

Naming loggers

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

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.

Making logging calls

The logger instance contains an entry method for each of the default
log levels:

  • logger.debug()
  • 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.




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 default) 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 simple configuration which writes all logging from the
django logger to a local file:

    '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

    '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:

    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'verbose': {
            'format': '%(levelname)s %(asctime)s %(module)s %(process)d %(thread)d %(message)s'
        'simple': {
            'format': '%(levelname)s %(message)s'
    '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 just 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
    • 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.

Custom logging configuration

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.

Disabling logging configuration

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:

import logging.config

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’s logging extensions¶

Django provides a number of utilities to handle the unique
requirements of logging in Web server environment.


Django provides several built-in loggers.


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.


Log messages related to the handling of requests. 5XX responses are
raised as ERROR messages; 4XX responses are raised as WARNING

Messages to this logger have the following extra context:

  • status_code: The HTTP response code associated with the
  • request: The request object that generated the logging


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.


Log messages related to the rendering of templates.

  • Missing context variables are logged as DEBUG messages.
  • Uncaught exceptions raised during the rendering of an
    {% include %} are logged as WARNING messages when
    debug mode is off (helpful since {% include %} silences the exception and
    returns an empty string in that case).


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.*

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 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 logger.

To silence a particular type of SuspiciousOperation, you can override that
specific logger following this example:

'handlers': {
    'null': {
        'class': 'logging.NullHandler',
'loggers': {
    '': {
        'handlers': ['null'],
        'propagate': False,

Other loggers not based on SuspiciousOperation are:


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.

class AdminEmailHandler(include_html=False, email_backend=None)[source]

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.

send_mail(subject, message, *args, **kwargs)[source]

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.

class CallbackFilter(callback)[source]

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'
class RequireDebugFalse[source]

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'
class RequireDebugTrue[source]

This filter is similar to RequireDebugFalse, except that records are
passed only when DEBUG is True.

Django’s default logging configuration¶

By default, Django configures the following logging:

When DEBUG is True:

  • The django logger sends messages in the django hierarchy (except
    django.server) at the INFO level or higher to the console.

When DEBUG is False:

  • The django logger sends messages in the django hierarchy (except
    django.server) with ERROR or CRITICAL level to

Independent of the value of DEBUG:

  • The django.server logger sends messages at the INFO level
    or higher to the console.

See also Configuring logging to learn how you can
complement or replace this default logging configuration.

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