576 lines
20 KiB
Plaintext
576 lines
20 KiB
Plaintext
=======
|
|
Logging
|
|
=======
|
|
|
|
.. module:: django.utils.log
|
|
:synopsis: Logging tools for Django applications
|
|
|
|
A quick logging primer
|
|
======================
|
|
|
|
Django uses Python's builtin :mod:`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:
|
|
|
|
* :ref:`topic-logging-parts-loggers`
|
|
* :ref:`topic-logging-parts-handlers`
|
|
* :ref:`topic-logging-parts-filters`
|
|
* :ref:`topic-logging-parts-formatters`
|
|
|
|
.. _topic-logging-parts-loggers:
|
|
|
|
Loggers
|
|
~~~~~~~
|
|
|
|
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
|
|
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*.
|
|
|
|
.. _topic-logging-parts-handlers:
|
|
|
|
Handlers
|
|
~~~~~~~~
|
|
|
|
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.
|
|
|
|
.. _topic-logging-parts-filters:
|
|
|
|
Filters
|
|
~~~~~~~
|
|
|
|
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.
|
|
|
|
.. _topic-logging-parts-formatters:
|
|
|
|
Formatters
|
|
~~~~~~~~~~
|
|
|
|
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; 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 :func:`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 it's 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.critical()``
|
|
* ``logger.error()``
|
|
* ``logger.warning()``
|
|
* ``logger.info()``
|
|
* ``logger.debug()``
|
|
|
|
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.
|
|
|
|
.. _configuring-logging:
|
|
|
|
Configuring logging
|
|
===================
|
|
|
|
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`_.
|
|
|
|
.. note::
|
|
``logging.dictConfig`` is a builtin library in Python 2.7. In
|
|
order to make this library available for users of earlier Python
|
|
versions, Django includes a copy as part of ``django.utils.log``.
|
|
If you have Python 2.7 or later, the system native library will be used; if
|
|
you have Python 2.6, Django's copy will be used.
|
|
|
|
In order to configure logging, you use :setting:`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.
|
|
|
|
Prior to Django 1.5, the :setting:`LOGGING` setting overwrote the :ref:`default
|
|
Django logging configuration <default-logging-configuration>`. From Django
|
|
1.5 forward, the project's logging configuration is merged with Django's
|
|
defaults, hence you can decide if you want to add to, or replace the existing
|
|
configuration. To completely override the default configuration, set the
|
|
``disable_existing_loggers`` key to True in the :setting:`LOGGING`
|
|
dictConfig. Alternatively you can redefine some or all of the loggers.
|
|
|
|
Logging is configured as soon as settings have been loaded
|
|
(either manually using :func:`~django.conf.settings.configure` or when at least
|
|
one setting is accessed). Since the loading of settings is one of the first
|
|
things that Django does, you can be certain that loggers are always ready for
|
|
use in your project code.
|
|
|
|
.. _dictConfig format: http://docs.python.org/library/logging.config.html#configuration-dictionary-schema
|
|
|
|
.. _a third-party library: http://bitbucket.org/vinay.sajip/dictconfig
|
|
|
|
An example
|
|
----------
|
|
|
|
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 is an example of a fairly
|
|
complex logging setup, configured using :func:`logging.config.dictConfig`::
|
|
|
|
LOGGING = {
|
|
'version': 1,
|
|
'disable_existing_loggers': True,
|
|
'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',
|
|
}
|
|
},
|
|
'handlers': {
|
|
'null': {
|
|
'level': 'DEBUG',
|
|
'class': 'django.utils.log.NullHandler',
|
|
},
|
|
'console':{
|
|
'level': 'DEBUG',
|
|
'class': 'logging.StreamHandler',
|
|
'formatter': 'simple'
|
|
},
|
|
'mail_admins': {
|
|
'level': 'ERROR',
|
|
'class': 'django.utils.log.AdminEmailHandler',
|
|
'filters': ['special']
|
|
}
|
|
},
|
|
'loggers': {
|
|
'django': {
|
|
'handlers': ['null'],
|
|
'propagate': True,
|
|
'level': 'INFO',
|
|
},
|
|
'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.
|
|
|
|
* Disables all existing logging configurations.
|
|
|
|
* 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 the `formatter documentation`_.
|
|
|
|
* ``verbose``, that outputs the log level name, the log
|
|
message, plus the time, process, thread and module that
|
|
generate the log message.
|
|
|
|
* Defines one filter -- ``project.logging.SpecialFilter``,
|
|
using the alias ``special``. If this filter required additional
|
|
arguments at time of construction, 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 the ``SpecialFilter``.
|
|
|
|
* Defines three handlers:
|
|
|
|
* ``null``, a NullHandler, which will pass any ``DEBUG`` (or
|
|
higher) message to ``/dev/null``.
|
|
|
|
* ``console``, a StreamHandler, which will print any ``DEBUG``
|
|
(or higher) message to stderr. This handler uses the ``simple`` output
|
|
format.
|
|
|
|
* ``mail_admins``, an AdminEmailHandler, which will email any
|
|
``ERROR`` (or higher) message to the site admins. This handler uses
|
|
the ``special`` filter.
|
|
|
|
* Configures three loggers:
|
|
|
|
* ``django``, which passes all messages at ``INFO`` or higher
|
|
to the ``null`` 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.
|
|
|
|
.. _formatter documentation: http://docs.python.org/library/logging.html#formatter-objects
|
|
|
|
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 :setting:`LOGGING_CONFIG` setting defines the callable that will
|
|
be used to configure Django's loggers. By default, it points at
|
|
Python's :func:`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 :setting:`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
|
|
:setting:`LOGGING_CONFIG` to ``None``. This will disable the
|
|
configuration process.
|
|
|
|
.. note::
|
|
Setting :setting:`LOGGING_CONFIG` to ``None`` only means that the
|
|
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.
|
|
|
|
Loggers
|
|
-------
|
|
|
|
Django provides three built-in loggers.
|
|
|
|
``django``
|
|
~~~~~~~~~~
|
|
|
|
``django`` is the catch-all logger. No messages are posted directly to
|
|
this logger.
|
|
|
|
``django.request``
|
|
~~~~~~~~~~~~~~~~~~
|
|
|
|
Log messages related to the handling of requests. 5XX responses are
|
|
raised as ``ERROR`` messages; 4XX responses are raised as ``WARNING``
|
|
messages.
|
|
|
|
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.db.backends``
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Messages relating to the interaction of code with the database.
|
|
For example, every 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.
|
|
|
|
Handlers
|
|
--------
|
|
|
|
Django provides one log handler in addition to those provided by the
|
|
Python logging module.
|
|
|
|
.. class:: AdminEmailHandler([include_html=False])
|
|
|
|
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.
|
|
|
|
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 :setting:`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
|
|
:ref:`Filtering error reports<filtering-error-reports>`.
|
|
|
|
.. _Sentry: http://pypi.python.org/pypi/sentry
|
|
|
|
|
|
Filters
|
|
-------
|
|
|
|
Django provides two log filters in addition to those provided by the Python
|
|
logging module.
|
|
|
|
.. class:: CallbackFilter(callback)
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
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 :exc:`~django.http.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()
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
This filter will only pass on records when settings.DEBUG is False.
|
|
|
|
This filter is used as follows in the default :setting:`LOGGING`
|
|
configuration to ensure that the :class:`AdminEmailHandler` only sends error
|
|
emails to admins when :setting:`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()
|
|
|
|
.. versionadded:: 1.5
|
|
|
|
This filter is similar to :class:`RequireDebugFalse`, except that records are
|
|
passed only when :setting:`DEBUG` is ``True``.
|
|
|
|
.. _default-logging-configuration:
|
|
|
|
Django's default logging configuration
|
|
======================================
|
|
|
|
By default, Django configures the ``django.request`` logger so that all messages
|
|
with ``ERROR`` or ``CRITICAL`` level are sent to :class:`AdminEmailHandler`, as
|
|
long as the :setting:`DEBUG` setting is set to ``False``.
|
|
|
|
All messages reaching the ``django`` catch-all logger when :setting:`DEBUG` is
|
|
``True`` are sent to the console. They are simply discarded (sent to
|
|
``NullHandler``) when :setting:`DEBUG` is ``False``.
|
|
|
|
.. versionchanged:: 1.5
|
|
|
|
Before Django 1.5, all messages reaching the ``django`` logger were
|
|
discarded, regardless of :setting:`DEBUG`.
|
|
|
|
See also :ref:`Configuring logging <configuring-logging>` to learn how you can
|
|
complement or replace this default logging configuration.
|