| :mod:`logging` --- Logging facility for Python | |
| ============================================== | |
| .. module:: logging | |
| :synopsis: Flexible event logging system for applications. | |
| .. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com> | |
| .. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com> | |
| .. index:: pair: Errors; logging | |
| .. sidebar:: Important | |
| This page contains the API reference information. For tutorial | |
| information and discussion of more advanced topics, see | |
| * :ref:`Basic Tutorial <logging-basic-tutorial>` | |
| * :ref:`Advanced Tutorial <logging-advanced-tutorial>` | |
| * :ref:`Logging Cookbook <logging-cookbook>` | |
| **Source code:** :source:`Lib/logging/__init__.py` | |
| -------------- | |
| .. versionadded:: 2.3 | |
| This module defines functions and classes which implement a flexible event | |
| logging system for applications and libraries. | |
| The key benefit of having the logging API provided by a standard library module | |
| is that all Python modules can participate in logging, so your application log | |
| can include your own messages integrated with messages from third-party | |
| modules. | |
| The module provides a lot of functionality and flexibility. If you are | |
| unfamiliar with logging, the best way to get to grips with it is to see the | |
| tutorials (see the links on the right). | |
| The basic classes defined by the module, together with their functions, are | |
| listed below. | |
| * Loggers expose the interface that application code directly uses. | |
| * Handlers send the log records (created by loggers) to the appropriate | |
| destination. | |
| * Filters provide a finer grained facility for determining which log records | |
| to output. | |
| * Formatters specify the layout of log records in the final output. | |
| .. _logger: | |
| Logger Objects | |
| -------------- | |
| Loggers have the following attributes and methods. Note that Loggers are never | |
| instantiated directly, but always through the module-level function | |
| ``logging.getLogger(name)``. Multiple calls to :func:`getLogger` with the same | |
| name will always return a reference to the same Logger object. | |
| The ``name`` is potentially a period-separated hierarchical value, like | |
| ``foo.bar.baz`` (though it could also be just plain ``foo``, for example). | |
| Loggers that are further down in the hierarchical list are children of loggers | |
| higher up in the list. For example, given a logger with a name of ``foo``, | |
| loggers with names of ``foo.bar``, ``foo.bar.baz``, and ``foo.bam`` are all | |
| descendants of ``foo``. The logger name hierarchy is analogous to the Python | |
| package hierarchy, and identical to it if you organise your loggers on a | |
| per-module basis using the recommended construction | |
| ``logging.getLogger(__name__)``. That's because in a module, ``__name__`` | |
| is the module's name in the Python package namespace. | |
| .. class:: Logger | |
| .. attribute:: Logger.propagate | |
| If this evaluates to true, events logged to this logger will be passed to the | |
| handlers of higher level (ancestor) loggers, in addition to any handlers | |
| attached to this logger. Messages are passed directly to the ancestor | |
| loggers' handlers - neither the level nor filters of the ancestor loggers in | |
| question are considered. | |
| If this evaluates to false, logging messages are not passed to the handlers | |
| of ancestor loggers. | |
| The constructor sets this attribute to ``True``. | |
| .. note:: If you attach a handler to a logger *and* one or more of its | |
| ancestors, it may emit the same record multiple times. In general, you | |
| should not need to attach a handler to more than one logger - if you just | |
| attach it to the appropriate logger which is highest in the logger | |
| hierarchy, then it will see all events logged by all descendant loggers, | |
| provided that their propagate setting is left set to ``True``. A common | |
| scenario is to attach handlers only to the root logger, and to let | |
| propagation take care of the rest. | |
| .. method:: Logger.setLevel(lvl) | |
| Sets the threshold for this logger to *lvl*. Logging messages which are less | |
| severe than *lvl* will be ignored. When a logger is created, the level is set to | |
| :const:`NOTSET` (which causes all messages to be processed when the logger is | |
| the root logger, or delegation to the parent when the logger is a non-root | |
| logger). Note that the root logger is created with level :const:`WARNING`. | |
| The term 'delegation to the parent' means that if a logger has a level of | |
| NOTSET, its chain of ancestor loggers is traversed until either an ancestor with | |
| a level other than NOTSET is found, or the root is reached. | |
| If an ancestor is found with a level other than NOTSET, then that ancestor's | |
| level is treated as the effective level of the logger where the ancestor search | |
| began, and is used to determine how a logging event is handled. | |
| If the root is reached, and it has a level of NOTSET, then all messages will be | |
| processed. Otherwise, the root's level will be used as the effective level. | |
| See :ref:`levels` for a list of levels. | |
| .. method:: Logger.isEnabledFor(lvl) | |
| Indicates if a message of severity *lvl* would be processed by this logger. | |
| This method checks first the module-level level set by | |
| ``logging.disable(lvl)`` and then the logger's effective level as determined | |
| by :meth:`getEffectiveLevel`. | |
| .. method:: Logger.getEffectiveLevel() | |
| Indicates the effective level for this logger. If a value other than | |
| :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise, | |
| the hierarchy is traversed towards the root until a value other than | |
| :const:`NOTSET` is found, and that value is returned. The value returned is | |
| an integer, typically one of :const:`logging.DEBUG`, :const:`logging.INFO` | |
| etc. | |
| .. method:: Logger.getChild(suffix) | |
| Returns a logger which is a descendant to this logger, as determined by the suffix. | |
| Thus, ``logging.getLogger('abc').getChild('def.ghi')`` would return the same | |
| logger as would be returned by ``logging.getLogger('abc.def.ghi')``. This is a | |
| convenience method, useful when the parent logger is named using e.g. ``__name__`` | |
| rather than a literal string. | |
| .. versionadded:: 2.7 | |
| .. method:: Logger.debug(msg, *args, **kwargs) | |
| Logs a message with level :const:`DEBUG` on this logger. The *msg* is the | |
| message format string, and the *args* are the arguments which are merged into | |
| *msg* using the string formatting operator. (Note that this means that you can | |
| use keywords in the format string, together with a single dictionary argument.) | |
| There are two keyword arguments in *kwargs* which are inspected: *exc_info* | |
| which, if it does not evaluate as false, causes exception information to be | |
| added to the logging message. If an exception tuple (in the format returned by | |
| :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info` | |
| is called to get the exception information. | |
| The second keyword argument is *extra* which can be used to pass a | |
| dictionary which is used to populate the __dict__ of the LogRecord created for | |
| the logging event with user-defined attributes. These custom attributes can then | |
| be used as you like. For example, they could be incorporated into logged | |
| messages. For example:: | |
| FORMAT = '%(asctime)-15s %(clientip)s %(user)-8s %(message)s' | |
| logging.basicConfig(format=FORMAT) | |
| d = {'clientip': '192.168.0.1', 'user': 'fbloggs'} | |
| logger = logging.getLogger('tcpserver') | |
| logger.warning('Protocol problem: %s', 'connection reset', extra=d) | |
| would print something like :: | |
| 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset | |
| The keys in the dictionary passed in *extra* should not clash with the keys used | |
| by the logging system. (See the :class:`Formatter` documentation for more | |
| information on which keys are used by the logging system.) | |
| If you choose to use these attributes in logged messages, you need to exercise | |
| some care. In the above example, for instance, the :class:`Formatter` has been | |
| set up with a format string which expects 'clientip' and 'user' in the attribute | |
| dictionary of the LogRecord. If these are missing, the message will not be | |
| logged because a string formatting exception will occur. So in this case, you | |
| always need to pass the *extra* dictionary with these keys. | |
| While this might be annoying, this feature is intended for use in specialized | |
| circumstances, such as multi-threaded servers where the same code executes in | |
| many contexts, and interesting conditions which arise are dependent on this | |
| context (such as remote client IP address and authenticated user name, in the | |
| above example). In such circumstances, it is likely that specialized | |
| :class:`Formatter`\ s would be used with particular :class:`Handler`\ s. | |
| .. method:: Logger.info(msg, *args, **kwargs) | |
| Logs a message with level :const:`INFO` on this logger. The arguments are | |
| interpreted as for :meth:`debug`. | |
| .. method:: Logger.warning(msg, *args, **kwargs) | |
| Logs a message with level :const:`WARNING` on this logger. The arguments are | |
| interpreted as for :meth:`debug`. | |
| .. method:: Logger.error(msg, *args, **kwargs) | |
| Logs a message with level :const:`ERROR` on this logger. The arguments are | |
| interpreted as for :meth:`debug`. | |
| .. method:: Logger.critical(msg, *args, **kwargs) | |
| Logs a message with level :const:`CRITICAL` on this logger. The arguments are | |
| interpreted as for :meth:`debug`. | |
| .. method:: Logger.log(lvl, msg, *args, **kwargs) | |
| Logs a message with integer level *lvl* on this logger. The other arguments are | |
| interpreted as for :meth:`debug`. | |
| .. method:: Logger.exception(msg, *args, **kwargs) | |
| Logs a message with level :const:`ERROR` on this logger. The arguments are | |
| interpreted as for :meth:`debug`, except that any passed *exc_info* is not | |
| inspected. Exception info is always added to the logging message. This method | |
| should only be called from an exception handler. | |
| .. method:: Logger.addFilter(filt) | |
| Adds the specified filter *filt* to this logger. | |
| .. method:: Logger.removeFilter(filt) | |
| Removes the specified filter *filt* from this logger. | |
| .. method:: Logger.filter(record) | |
| Applies this logger's filters to the record and returns a true value if the | |
| record is to be processed. The filters are consulted in turn, until one of | |
| them returns a false value. If none of them return a false value, the record | |
| will be processed (passed to handlers). If one returns a false value, no | |
| further processing of the record occurs. | |
| .. method:: Logger.addHandler(hdlr) | |
| Adds the specified handler *hdlr* to this logger. | |
| .. method:: Logger.removeHandler(hdlr) | |
| Removes the specified handler *hdlr* from this logger. | |
| .. method:: Logger.findCaller() | |
| Finds the caller's source filename and line number. Returns the filename, line | |
| number and function name as a 3-element tuple. | |
| .. versionchanged:: 2.4 | |
| The function name was added. In earlier versions, the filename and line | |
| number were returned as a 2-element tuple. | |
| .. method:: Logger.handle(record) | |
| Handles a record by passing it to all handlers associated with this logger and | |
| its ancestors (until a false value of *propagate* is found). This method is used | |
| for unpickled records received from a socket, as well as those created locally. | |
| Logger-level filtering is applied using :meth:`~Logger.filter`. | |
| .. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info, func=None, extra=None) | |
| This is a factory method which can be overridden in subclasses to create | |
| specialized :class:`LogRecord` instances. | |
| .. versionchanged:: 2.5 | |
| *func* and *extra* were added. | |
| .. _levels: | |
| Logging Levels | |
| -------------- | |
| The numeric values of logging levels are given in the following table. These are | |
| primarily of interest if you want to define your own levels, and need them to | |
| have specific values relative to the predefined levels. If you define a level | |
| with the same numeric value, it overwrites the predefined value; the predefined | |
| name is lost. | |
| +--------------+---------------+ | |
| | Level | Numeric value | | |
| +==============+===============+ | |
| | ``CRITICAL`` | 50 | | |
| +--------------+---------------+ | |
| | ``ERROR`` | 40 | | |
| +--------------+---------------+ | |
| | ``WARNING`` | 30 | | |
| +--------------+---------------+ | |
| | ``INFO`` | 20 | | |
| +--------------+---------------+ | |
| | ``DEBUG`` | 10 | | |
| +--------------+---------------+ | |
| | ``NOTSET`` | 0 | | |
| +--------------+---------------+ | |
| .. _handler: | |
| Handler Objects | |
| --------------- | |
| Handlers have the following attributes and methods. Note that :class:`Handler` | |
| is never instantiated directly; this class acts as a base for more useful | |
| subclasses. However, the :meth:`__init__` method in subclasses needs to call | |
| :meth:`Handler.__init__`. | |
| .. method:: Handler.__init__(level=NOTSET) | |
| Initializes the :class:`Handler` instance by setting its level, setting the list | |
| of filters to the empty list and creating a lock (using :meth:`createLock`) for | |
| serializing access to an I/O mechanism. | |
| .. method:: Handler.createLock() | |
| Initializes a thread lock which can be used to serialize access to underlying | |
| I/O functionality which may not be threadsafe. | |
| .. method:: Handler.acquire() | |
| Acquires the thread lock created with :meth:`createLock`. | |
| .. method:: Handler.release() | |
| Releases the thread lock acquired with :meth:`acquire`. | |
| .. method:: Handler.setLevel(lvl) | |
| Sets the threshold for this handler to *lvl*. Logging messages which are less | |
| severe than *lvl* will be ignored. When a handler is created, the level is set | |
| to :const:`NOTSET` (which causes all messages to be processed). | |
| See :ref:`levels` for a list of levels. | |
| .. method:: Handler.setFormatter(form) | |
| Sets the :class:`Formatter` for this handler to *form*. | |
| .. method:: Handler.addFilter(filt) | |
| Adds the specified filter *filt* to this handler. | |
| .. method:: Handler.removeFilter(filt) | |
| Removes the specified filter *filt* from this handler. | |
| .. method:: Handler.filter(record) | |
| Applies this handler's filters to the record and returns a true value if the | |
| record is to be processed. The filters are consulted in turn, until one of | |
| them returns a false value. If none of them return a false value, the record | |
| will be emitted. If one returns a false value, the handler will not emit the | |
| record. | |
| .. method:: Handler.flush() | |
| Ensure all logging output has been flushed. This version does nothing and is | |
| intended to be implemented by subclasses. | |
| .. method:: Handler.close() | |
| Tidy up any resources used by the handler. This version does no output but | |
| removes the handler from an internal list of handlers which is closed when | |
| :func:`shutdown` is called. Subclasses should ensure that this gets called | |
| from overridden :meth:`close` methods. | |
| .. method:: Handler.handle(record) | |
| Conditionally emits the specified logging record, depending on filters which may | |
| have been added to the handler. Wraps the actual emission of the record with | |
| acquisition/release of the I/O thread lock. | |
| .. method:: Handler.handleError(record) | |
| This method should be called from handlers when an exception is encountered | |
| during an :meth:`emit` call. If the module-level attribute | |
| ``raiseExceptions`` is ``False``, exceptions get silently ignored. This is | |
| what is mostly wanted for a logging system - most users will not care about | |
| errors in the logging system, they are more interested in application | |
| errors. You could, however, replace this with a custom handler if you wish. | |
| The specified record is the one which was being processed when the exception | |
| occurred. (The default value of ``raiseExceptions`` is ``True``, as that is | |
| more useful during development). | |
| .. method:: Handler.format(record) | |
| Do formatting for a record - if a formatter is set, use it. Otherwise, use the | |
| default formatter for the module. | |
| .. method:: Handler.emit(record) | |
| Do whatever it takes to actually log the specified logging record. This version | |
| is intended to be implemented by subclasses and so raises a | |
| :exc:`NotImplementedError`. | |
| For a list of handlers included as standard, see :mod:`logging.handlers`. | |
| .. _formatter-objects: | |
| Formatter Objects | |
| ----------------- | |
| .. currentmodule:: logging | |
| :class:`Formatter` objects have the following attributes and methods. They are | |
| responsible for converting a :class:`LogRecord` to (usually) a string which can | |
| be interpreted by either a human or an external system. The base | |
| :class:`Formatter` allows a formatting string to be specified. If none is | |
| supplied, the default value of ``'%(message)s'`` is used, which just includes | |
| the message in the logging call. To have additional items of information in the | |
| formatted output (such as a timestamp), keep reading. | |
| A Formatter can be initialized with a format string which makes use of knowledge | |
| of the :class:`LogRecord` attributes - such as the default value mentioned above | |
| making use of the fact that the user's message and arguments are pre-formatted | |
| into a :class:`LogRecord`'s *message* attribute. This format string contains | |
| standard Python %-style mapping keys. See section :ref:`string-formatting` | |
| for more information on string formatting. | |
| The useful mapping keys in a :class:`LogRecord` are given in the section on | |
| :ref:`logrecord-attributes`. | |
| .. class:: Formatter(fmt=None, datefmt=None) | |
| Returns a new instance of the :class:`Formatter` class. The instance is | |
| initialized with a format string for the message as a whole, as well as a | |
| format string for the date/time portion of a message. If no *fmt* is | |
| specified, ``'%(message)s'`` is used. If no *datefmt* is specified, the | |
| ISO8601 date format is used. | |
| .. method:: format(record) | |
| The record's attribute dictionary is used as the operand to a string | |
| formatting operation. Returns the resulting string. Before formatting the | |
| dictionary, a couple of preparatory steps are carried out. The *message* | |
| attribute of the record is computed using *msg* % *args*. If the | |
| formatting string contains ``'(asctime)'``, :meth:`formatTime` is called | |
| to format the event time. If there is exception information, it is | |
| formatted using :meth:`formatException` and appended to the message. Note | |
| that the formatted exception information is cached in attribute | |
| *exc_text*. This is useful because the exception information can be | |
| pickled and sent across the wire, but you should be careful if you have | |
| more than one :class:`Formatter` subclass which customizes the formatting | |
| of exception information. In this case, you will have to clear the cached | |
| value after a formatter has done its formatting, so that the next | |
| formatter to handle the event doesn't use the cached value but | |
| recalculates it afresh. | |
| .. method:: formatTime(record, datefmt=None) | |
| This method should be called from :meth:`format` by a formatter which | |
| wants to make use of a formatted time. This method can be overridden in | |
| formatters to provide for any specific requirement, but the basic behavior | |
| is as follows: if *datefmt* (a string) is specified, it is used with | |
| :func:`time.strftime` to format the creation time of the | |
| record. Otherwise, the ISO8601 format is used. The resulting string is | |
| returned. | |
| This function uses a user-configurable function to convert the creation | |
| time to a tuple. By default, :func:`time.localtime` is used; to change | |
| this for a particular formatter instance, set the ``converter`` attribute | |
| to a function with the same signature as :func:`time.localtime` or | |
| :func:`time.gmtime`. To change it for all formatters, for example if you | |
| want all logging times to be shown in GMT, set the ``converter`` | |
| attribute in the ``Formatter`` class. | |
| .. method:: formatException(exc_info) | |
| Formats the specified exception information (a standard exception tuple as | |
| returned by :func:`sys.exc_info`) as a string. This default implementation | |
| just uses :func:`traceback.print_exception`. The resulting string is | |
| returned. | |
| .. _filter: | |
| Filter Objects | |
| -------------- | |
| ``Filters`` can be used by ``Handlers`` and ``Loggers`` for more sophisticated | |
| filtering than is provided by levels. The base filter class only allows events | |
| which are below a certain point in the logger hierarchy. For example, a filter | |
| initialized with 'A.B' will allow events logged by loggers 'A.B', 'A.B.C', | |
| 'A.B.C.D', 'A.B.D' etc. but not 'A.BB', 'B.A.B' etc. If initialized with the | |
| empty string, all events are passed. | |
| .. class:: Filter(name='') | |
| Returns an instance of the :class:`Filter` class. If *name* is specified, it | |
| names a logger which, together with its children, will have its events allowed | |
| through the filter. If *name* is the empty string, allows every event. | |
| .. method:: filter(record) | |
| Is the specified record to be logged? Returns zero for no, nonzero for | |
| yes. If deemed appropriate, the record may be modified in-place by this | |
| method. | |
| Note that filters attached to handlers are consulted before an event is | |
| emitted by the handler, whereas filters attached to loggers are consulted | |
| whenever an event is logged (using :meth:`debug`, :meth:`info`, | |
| etc.), before sending an event to handlers. This means that events which have | |
| been generated by descendant loggers will not be filtered by a logger's filter | |
| setting, unless the filter has also been applied to those descendant loggers. | |
| You don't actually need to subclass ``Filter``: you can pass any instance | |
| which has a ``filter`` method with the same semantics. | |
| Although filters are used primarily to filter records based on more | |
| sophisticated criteria than levels, they get to see every record which is | |
| processed by the handler or logger they're attached to: this can be useful if | |
| you want to do things like counting how many records were processed by a | |
| particular logger or handler, or adding, changing or removing attributes in | |
| the LogRecord being processed. Obviously changing the LogRecord needs to be | |
| done with some care, but it does allow the injection of contextual information | |
| into logs (see :ref:`filters-contextual`). | |
| .. _log-record: | |
| LogRecord Objects | |
| ----------------- | |
| :class:`LogRecord` instances are created automatically by the :class:`Logger` | |
| every time something is logged, and can be created manually via | |
| :func:`makeLogRecord` (for example, from a pickled event received over the | |
| wire). | |
| .. class:: LogRecord(name, level, pathname, lineno, msg, args, exc_info, func=None) | |
| Contains all the information pertinent to the event being logged. | |
| The primary information is passed in :attr:`msg` and :attr:`args`, which | |
| are combined using ``msg % args`` to create the :attr:`message` field of the | |
| record. | |
| :param name: The name of the logger used to log the event represented by | |
| this LogRecord. Note that this name will always have this | |
| value, even though it may be emitted by a handler attached to | |
| a different (ancestor) logger. | |
| :param level: The numeric level of the logging event (one of DEBUG, INFO etc.) | |
| Note that this is converted to *two* attributes of the LogRecord: | |
| ``levelno`` for the numeric value and ``levelname`` for the | |
| corresponding level name. | |
| :param pathname: The full pathname of the source file where the logging call | |
| was made. | |
| :param lineno: The line number in the source file where the logging call was | |
| made. | |
| :param msg: The event description message, possibly a format string with | |
| placeholders for variable data. | |
| :param args: Variable data to merge into the *msg* argument to obtain the | |
| event description. | |
| :param exc_info: An exception tuple with the current exception information, | |
| or ``None`` if no exception information is available. | |
| :param func: The name of the function or method from which the logging call | |
| was invoked. | |
| .. versionchanged:: 2.5 | |
| *func* was added. | |
| .. method:: getMessage() | |
| Returns the message for this :class:`LogRecord` instance after merging any | |
| user-supplied arguments with the message. If the user-supplied message | |
| argument to the logging call is not a string, :func:`str` is called on it to | |
| convert it to a string. This allows use of user-defined classes as | |
| messages, whose ``__str__`` method can return the actual format string to | |
| be used. | |
| .. _logrecord-attributes: | |
| LogRecord attributes | |
| -------------------- | |
| The LogRecord has a number of attributes, most of which are derived from the | |
| parameters to the constructor. (Note that the names do not always correspond | |
| exactly between the LogRecord constructor parameters and the LogRecord | |
| attributes.) These attributes can be used to merge data from the record into | |
| the format string. The following table lists (in alphabetical order) the | |
| attribute names, their meanings and the corresponding placeholder in a %-style | |
| format string. | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | Attribute name | Format | Description | | |
| +================+=========================+===============================================+ | |
| | args | You shouldn't need to | The tuple of arguments merged into ``msg`` to | | |
| | | format this yourself. | produce ``message``, or a dict whose values | | |
| | | | are used for the merge (when there is only one| | |
| | | | argument, and it is a dictionary). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | asctime | ``%(asctime)s`` | Human-readable time when the | | |
| | | | :class:`LogRecord` was created. By default | | |
| | | | this is of the form '2003-07-08 16:49:45,896' | | |
| | | | (the numbers after the comma are millisecond | | |
| | | | portion of the time). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | created | ``%(created)f`` | Time when the :class:`LogRecord` was created | | |
| | | | (as returned by :func:`time.time`). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | exc_info | You shouldn't need to | Exception tuple (Ã la ``sys.exc_info``) or, | | |
| | | format this yourself. | if no exception has occurred, ``None``. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | filename | ``%(filename)s`` | Filename portion of ``pathname``. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | funcName | ``%(funcName)s`` | Name of function containing the logging call. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | levelname | ``%(levelname)s`` | Text logging level for the message | | |
| | | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, | | |
| | | | ``'ERROR'``, ``'CRITICAL'``). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | levelno | ``%(levelno)s`` | Numeric logging level for the message | | |
| | | | (:const:`DEBUG`, :const:`INFO`, | | |
| | | | :const:`WARNING`, :const:`ERROR`, | | |
| | | | :const:`CRITICAL`). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | lineno | ``%(lineno)d`` | Source line number where the logging call was | | |
| | | | issued (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | module | ``%(module)s`` | Module (name portion of ``filename``). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | msecs | ``%(msecs)d`` | Millisecond portion of the time when the | | |
| | | | :class:`LogRecord` was created. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | message | ``%(message)s`` | The logged message, computed as ``msg % | | |
| | | | args``. This is set when | | |
| | | | :meth:`Formatter.format` is invoked. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | msg | You shouldn't need to | The format string passed in the original | | |
| | | format this yourself. | logging call. Merged with ``args`` to | | |
| | | | produce ``message``, or an arbitrary object | | |
| | | | (see :ref:`arbitrary-object-messages`). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | name | ``%(name)s`` | Name of the logger used to log the call. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | pathname | ``%(pathname)s`` | Full pathname of the source file where the | | |
| | | | logging call was issued (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | process | ``%(process)d`` | Process ID (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | processName | ``%(processName)s`` | Process name (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | relativeCreated| ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was | | |
| | | | created, relative to the time the logging | | |
| | | | module was loaded. | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | thread | ``%(thread)d`` | Thread ID (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| | threadName | ``%(threadName)s`` | Thread name (if available). | | |
| +----------------+-------------------------+-----------------------------------------------+ | |
| .. versionchanged:: 2.5 | |
| *funcName* was added. | |
| .. versionchanged:: 2.6 | |
| *processName* was added. | |
| .. _logger-adapter: | |
| LoggerAdapter Objects | |
| --------------------- | |
| :class:`LoggerAdapter` instances are used to conveniently pass contextual | |
| information into logging calls. For a usage example, see the section on | |
| :ref:`adding contextual information to your logging output <context-info>`. | |
| .. versionadded:: 2.6 | |
| .. class:: LoggerAdapter(logger, extra) | |
| Returns an instance of :class:`LoggerAdapter` initialized with an | |
| underlying :class:`Logger` instance and a dict-like object. | |
| .. method:: process(msg, kwargs) | |
| Modifies the message and/or keyword arguments passed to a logging call in | |
| order to insert contextual information. This implementation takes the object | |
| passed as *extra* to the constructor and adds it to *kwargs* using key | |
| 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the | |
| (possibly modified) versions of the arguments passed in. | |
| In addition to the above, :class:`LoggerAdapter` supports the following | |
| methods of :class:`Logger`: :meth:`~Logger.debug`, :meth:`~Logger.info`, | |
| :meth:`~Logger.warning`, :meth:`~Logger.error`, :meth:`~Logger.exception`, | |
| :meth:`~Logger.critical`, :meth:`~Logger.log` and :meth:`~Logger.isEnabledFor`. | |
| These methods have the same signatures as their counterparts in :class:`Logger`, | |
| so you can use the two types of instances interchangeably for these calls. | |
| .. versionchanged:: 2.7 | |
| The :meth:`~Logger.isEnabledFor` method was added to :class:`LoggerAdapter`. | |
| This method delegates to the underlying logger. | |
| Thread Safety | |
| ------------- | |
| The logging module is intended to be thread-safe without any special work | |
| needing to be done by its clients. It achieves this though using threading | |
| locks; there is one lock to serialize access to the module's shared data, and | |
| each handler also creates a lock to serialize access to its underlying I/O. | |
| If you are implementing asynchronous signal handlers using the :mod:`signal` | |
| module, you may not be able to use logging from within such handlers. This is | |
| because lock implementations in the :mod:`threading` module are not always | |
| re-entrant, and so cannot be invoked from such signal handlers. | |
| Module-Level Functions | |
| ---------------------- | |
| In addition to the classes described above, there are a number of module- level | |
| functions. | |
| .. function:: getLogger([name]) | |
| Return a logger with the specified name or, if no name is specified, return a | |
| logger which is the root logger of the hierarchy. If specified, the name is | |
| typically a dot-separated hierarchical name like *"a"*, *"a.b"* or *"a.b.c.d"*. | |
| Choice of these names is entirely up to the developer who is using logging. | |
| All calls to this function with a given name return the same logger instance. | |
| This means that logger instances never need to be passed between different parts | |
| of an application. | |
| .. function:: getLoggerClass() | |
| Return either the standard :class:`Logger` class, or the last class passed to | |
| :func:`setLoggerClass`. This function may be called from within a new class | |
| definition, to ensure that installing a customized :class:`Logger` class will | |
| not undo customizations already applied by other code. For example:: | |
| class MyLogger(logging.getLoggerClass()): | |
| # ... override behaviour here | |
| .. function:: debug(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`DEBUG` on the root logger. The *msg* is the | |
| message format string, and the *args* are the arguments which are merged into | |
| *msg* using the string formatting operator. (Note that this means that you can | |
| use keywords in the format string, together with a single dictionary argument.) | |
| There are two keyword arguments in *kwargs* which are inspected: *exc_info* | |
| which, if it does not evaluate as false, causes exception information to be | |
| added to the logging message. If an exception tuple (in the format returned by | |
| :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info` | |
| is called to get the exception information. | |
| The other optional keyword argument is *extra* which can be used to pass a | |
| dictionary which is used to populate the __dict__ of the LogRecord created for | |
| the logging event with user-defined attributes. These custom attributes can then | |
| be used as you like. For example, they could be incorporated into logged | |
| messages. For example:: | |
| FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s" | |
| logging.basicConfig(format=FORMAT) | |
| d = {'clientip': '192.168.0.1', 'user': 'fbloggs'} | |
| logging.warning("Protocol problem: %s", "connection reset", extra=d) | |
| would print something like:: | |
| 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset | |
| The keys in the dictionary passed in *extra* should not clash with the keys used | |
| by the logging system. (See the :class:`Formatter` documentation for more | |
| information on which keys are used by the logging system.) | |
| If you choose to use these attributes in logged messages, you need to exercise | |
| some care. In the above example, for instance, the :class:`Formatter` has been | |
| set up with a format string which expects 'clientip' and 'user' in the attribute | |
| dictionary of the LogRecord. If these are missing, the message will not be | |
| logged because a string formatting exception will occur. So in this case, you | |
| always need to pass the *extra* dictionary with these keys. | |
| While this might be annoying, this feature is intended for use in specialized | |
| circumstances, such as multi-threaded servers where the same code executes in | |
| many contexts, and interesting conditions which arise are dependent on this | |
| context (such as remote client IP address and authenticated user name, in the | |
| above example). In such circumstances, it is likely that specialized | |
| :class:`Formatter`\ s would be used with particular :class:`Handler`\ s. | |
| .. versionchanged:: 2.5 | |
| *extra* was added. | |
| .. function:: info(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`INFO` on the root logger. The arguments are | |
| interpreted as for :func:`debug`. | |
| .. function:: warning(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`WARNING` on the root logger. The arguments are | |
| interpreted as for :func:`debug`. | |
| .. function:: error(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`ERROR` on the root logger. The arguments are | |
| interpreted as for :func:`debug`. | |
| .. function:: critical(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`CRITICAL` on the root logger. The arguments | |
| are interpreted as for :func:`debug`. | |
| .. function:: exception(msg[, *args[, **kwargs]]) | |
| Logs a message with level :const:`ERROR` on the root logger. The arguments are | |
| interpreted as for :func:`debug`, except that any passed *exc_info* is not | |
| inspected. Exception info is always added to the logging message. This | |
| function should only be called from an exception handler. | |
| .. function:: log(level, msg[, *args[, **kwargs]]) | |
| Logs a message with level *level* on the root logger. The other arguments are | |
| interpreted as for :func:`debug`. | |
| .. note:: The above module-level convenience functions, which delegate to the | |
| root logger, call :func:`basicConfig` to ensure that at least one handler | |
| is available. Because of this, they should *not* be used in threads, | |
| in versions of Python earlier than 2.7.1 and 3.2, unless at least one | |
| handler has been added to the root logger *before* the threads are | |
| started. In earlier versions of Python, due to a thread safety shortcoming | |
| in :func:`basicConfig`, this can (under rare circumstances) lead to | |
| handlers being added multiple times to the root logger, which can in turn | |
| lead to multiple messages for the same event. | |
| .. function:: disable(lvl) | |
| Provides an overriding level *lvl* for all loggers which takes precedence over | |
| the logger's own level. When the need arises to temporarily throttle logging | |
| output down across the whole application, this function can be useful. Its | |
| effect is to disable all logging calls of severity *lvl* and below, so that | |
| if you call it with a value of INFO, then all INFO and DEBUG events would be | |
| discarded, whereas those of severity WARNING and above would be processed | |
| according to the logger's effective level. If | |
| ``logging.disable(logging.NOTSET)`` is called, it effectively removes this | |
| overriding level, so that logging output again depends on the effective | |
| levels of individual loggers. | |
| .. function:: addLevelName(lvl, levelName) | |
| Associates level *lvl* with text *levelName* in an internal dictionary, which is | |
| used to map numeric levels to a textual representation, for example when a | |
| :class:`Formatter` formats a message. This function can also be used to define | |
| your own levels. The only constraints are that all levels used must be | |
| registered using this function, levels should be positive integers and they | |
| should increase in increasing order of severity. | |
| .. note:: If you are thinking of defining your own levels, please see the | |
| section on :ref:`custom-levels`. | |
| .. function:: getLevelName(lvl) | |
| Returns the textual representation of logging level *lvl*. If the level is one | |
| of the predefined levels :const:`CRITICAL`, :const:`ERROR`, :const:`WARNING`, | |
| :const:`INFO` or :const:`DEBUG` then you get the corresponding string. If you | |
| have associated levels with names using :func:`addLevelName` then the name you | |
| have associated with *lvl* is returned. If a numeric value corresponding to one | |
| of the defined levels is passed in, the corresponding string representation is | |
| returned. Otherwise, the string "Level %s" % lvl is returned. | |
| .. note:: Integer levels should be used when e.g. setting levels on instances | |
| of :class:`Logger` and handlers. This function is used to convert between | |
| an integer level and the level name displayed in the formatted log output | |
| by means of the ``%(levelname)s`` format specifier (see | |
| :ref:`logrecord-attributes`). | |
| .. function:: makeLogRecord(attrdict) | |
| Creates and returns a new :class:`LogRecord` instance whose attributes are | |
| defined by *attrdict*. This function is useful for taking a pickled | |
| :class:`LogRecord` attribute dictionary, sent over a socket, and reconstituting | |
| it as a :class:`LogRecord` instance at the receiving end. | |
| .. function:: basicConfig([**kwargs]) | |
| Does basic configuration for the logging system by creating a | |
| :class:`StreamHandler` with a default :class:`Formatter` and adding it to the | |
| root logger. The functions :func:`debug`, :func:`info`, :func:`warning`, | |
| :func:`error` and :func:`critical` will call :func:`basicConfig` automatically | |
| if no handlers are defined for the root logger. | |
| This function does nothing if the root logger already has handlers | |
| configured for it. | |
| .. versionchanged:: 2.4 | |
| Formerly, :func:`basicConfig` did not take any keyword arguments. | |
| .. note:: This function should be called from the main thread before other | |
| threads are started. In versions of Python prior to 2.7.1 and 3.2, if | |
| this function is called from multiple threads, it is possible (in rare | |
| circumstances) that a handler will be added to the root logger more than | |
| once, leading to unexpected results such as messages being duplicated in | |
| the log. | |
| The following keyword arguments are supported. | |
| .. tabularcolumns:: |l|L| | |
| +--------------+---------------------------------------------+ | |
| | Format | Description | | |
| +==============+=============================================+ | |
| | ``filename`` | Specifies that a FileHandler be created, | | |
| | | using the specified filename, rather than a | | |
| | | StreamHandler. | | |
| +--------------+---------------------------------------------+ | |
| | ``filemode`` | Specifies the mode to open the file, if | | |
| | | filename is specified (if filemode is | | |
| | | unspecified, it defaults to 'a'). | | |
| +--------------+---------------------------------------------+ | |
| | ``format`` | Use the specified format string for the | | |
| | | handler. | | |
| +--------------+---------------------------------------------+ | |
| | ``datefmt`` | Use the specified date/time format. | | |
| +--------------+---------------------------------------------+ | |
| | ``level`` | Set the root logger level to the specified | | |
| | | level. | | |
| +--------------+---------------------------------------------+ | |
| | ``stream`` | Use the specified stream to initialize the | | |
| | | StreamHandler. Note that this argument is | | |
| | | incompatible with 'filename' - if both are | | |
| | | present, 'stream' is ignored. | | |
| +--------------+---------------------------------------------+ | |
| .. function:: shutdown() | |
| Informs the logging system to perform an orderly shutdown by flushing and | |
| closing all handlers. This should be called at application exit and no | |
| further use of the logging system should be made after this call. | |
| .. function:: setLoggerClass(klass) | |
| Tells the logging system to use the class *klass* when instantiating a logger. | |
| The class should define :meth:`__init__` such that only a name argument is | |
| required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This | |
| function is typically called before any loggers are instantiated by applications | |
| which need to use custom logger behavior. | |
| Integration with the warnings module | |
| ------------------------------------ | |
| The :func:`captureWarnings` function can be used to integrate :mod:`logging` | |
| with the :mod:`warnings` module. | |
| .. function:: captureWarnings(capture) | |
| This function is used to turn the capture of warnings by logging on and | |
| off. | |
| If *capture* is ``True``, warnings issued by the :mod:`warnings` module will | |
| be redirected to the logging system. Specifically, a warning will be | |
| formatted using :func:`warnings.formatwarning` and the resulting string | |
| logged to a logger named ``'py.warnings'`` with a severity of :const:`WARNING`. | |
| If *capture* is ``False``, the redirection of warnings to the logging system | |
| will stop, and warnings will be redirected to their original destinations | |
| (i.e. those in effect before ``captureWarnings(True)`` was called). | |
| .. seealso:: | |
| Module :mod:`logging.config` | |
| Configuration API for the logging module. | |
| Module :mod:`logging.handlers` | |
| Useful handlers included with the logging module. | |
| :pep:`282` - A Logging System | |
| The proposal which described this feature for inclusion in the Python standard | |
| library. | |
| `Original Python logging package <https://www.red-dove.com/python_logging.html>`_ | |
| This is the original source for the :mod:`logging` package. The version of the | |
| package available from this site is suitable for use with Python 1.5.2, 2.1.x | |
| and 2.2.x, which do not include the :mod:`logging` package in the standard | |
| library. | |