
``logging`` --- Logging facility for Python
*******************************************


Important
^^^^^^^^^

This page contains the API reference information. For tutorial
information and discussion of more advanced topics, see

* *Basic Tutorial*

* *Advanced Tutorial*

* *Logging Cookbook*

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 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)``.

class class logging.Logger

Logger.propagate

   If this evaluates to false, logging messages are not passed by this
   logger or by its child loggers to the handlers of higher level
   (ancestor) loggers. The constructor sets this attribute to 1.

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 ``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 ``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.

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 ``getEffectiveLevel()``.

Logger.getEffectiveLevel()

   Indicates the effective level for this logger. If a value other
   than ``NOTSET`` has been set using ``setLevel()``, it is returned.
   Otherwise, the hierarchy is traversed towards the root until a
   value other than ``NOTSET`` is found, and that value is returned.

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.

   New in version 3.2.

Logger.debug(msg, *args, **kwargs)

   Logs a message with level ``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 three 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 ``sys.exc_info()``) is
   provided, it is used; otherwise, ``sys.exc_info()`` is called to
   get the exception information.

   The second optional keyword argument is *stack_info*, which
   defaults to False. If specified as True, stack information is added
   to the logging message, including the actual logging call. Note
   that this is not the same stack information as that displayed
   through specifying *exc_info*: The former is stack frames from the
   bottom of the stack up to the logging call in the current thread,
   whereas the latter is information about stack frames which have
   been unwound, following an exception, while searching for exception
   handlers.

   You can specify *stack_info* independently of *exc_info*, e.g. to
   just show how you got to a certain point in your code, even when no
   exceptions were raised. The stack frames are printed following a
   header line which says:

      Stack (most recent call last):

   This mimics the *Traceback (most recent call last):* which is used
   when displaying exception frames.

   The third 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 ``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
   ``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 ``Formatter``s would
   be used with particular ``Handler``s.

   New in version 3.2: The *stack_info* parameter was added.

Logger.info(msg, *args, **kwargs)

   Logs a message with level ``INFO`` on this logger. The arguments
   are interpreted as for ``debug()``.

Logger.warning(msg, *args, **kwargs)

   Logs a message with level ``WARNING`` on this logger. The arguments
   are interpreted as for ``debug()``.

Logger.error(msg, *args, **kwargs)

   Logs a message with level ``ERROR`` on this logger. The arguments
   are interpreted as for ``debug()``.

Logger.critical(msg, *args, **kwargs)

   Logs a message with level ``CRITICAL`` on this logger. The
   arguments are interpreted as for ``debug()``.

Logger.log(lvl, msg, *args, **kwargs)

   Logs a message with integer level *lvl* on this logger. The other
   arguments are interpreted as for ``debug()``.

Logger.exception(msg, *args)

   Logs a message with level ``ERROR`` on this logger. The arguments
   are interpreted as for ``debug()``. Exception info is added to the
   logging message. This method should only be called from an
   exception handler.

Logger.addFilter(filt)

   Adds the specified filter *filt* to this logger.

Logger.removeFilter(filt)

   Removes the specified filter *filt* from this logger.

Logger.filter(record)

   Applies this logger's filters to the record and returns a true
   value if the record is to be processed.

Logger.addHandler(hdlr)

   Adds the specified handler *hdlr* to this logger.

Logger.removeHandler(hdlr)

   Removes the specified handler *hdlr* from this logger.

Logger.findCaller(stack_info=False)

   Finds the caller's source filename and line number. Returns the
   filename, line number, function name and stack information as a
   4-element tuple. The stack information is returned as *None* unless
   *stack_info* is *True*.

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 ``filter()``.

Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info, func=None, extra=None, sinfo=None)

   This is a factory method which can be overridden in subclasses to
   create specialized ``LogRecord`` instances.

Logger.hasHandlers()

   Checks to see if this logger has any handlers configured. This is
   done by looking for handlers in this logger and its parents in the
   logger hierarchy. Returns True if a handler was found, else False.
   The method stops searching up the hierarchy whenever a logger with
   the 'propagate' attribute set to False is found - that will be the
   last logger which is checked for the existence of handlers.

   New in version 3.2.


Handler Objects
===============

Handlers have the following attributes and methods. Note that
``Handler`` is never instantiated directly; this class acts as a base
for more useful subclasses. However, the ``__init__()`` method in
subclasses needs to call ``Handler.__init__()``.

Handler.__init__(level=NOTSET)

   Initializes the ``Handler`` instance by setting its level, setting
   the list of filters to the empty list and creating a lock (using
   ``createLock()``) for serializing access to an I/O mechanism.

Handler.createLock()

   Initializes a thread lock which can be used to serialize access to
   underlying I/O functionality which may not be threadsafe.

Handler.acquire()

   Acquires the thread lock created with ``createLock()``.

Handler.release()

   Releases the thread lock acquired with ``acquire()``.

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 ``NOTSET`` (which causes all messages
   to be processed).

Handler.setFormatter(form)

   Sets the ``Formatter`` for this handler to *form*.

Handler.addFilter(filt)

   Adds the specified filter *filt* to this handler.

Handler.removeFilter(filt)

   Removes the specified filter *filt* from this handler.

Handler.filter(record)

   Applies this handler's filters to the record and returns a true
   value if the record is to be processed.

Handler.flush()

   Ensure all logging output has been flushed. This version does
   nothing and is intended to be implemented by subclasses.

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 ``shutdown()`` is called. Subclasses should
   ensure that this gets called from overridden ``close()`` methods.

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.

Handler.handleError(record)

   This method should be called from handlers when an exception is
   encountered during an ``emit()`` call. By default it does nothing,
   which means that 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.

Handler.format(record)

   Do formatting for a record - if a formatter is set, use it.
   Otherwise, use the default formatter for the module.

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 ``NotImplementedError``.

For a list of handlers included as standard, see ``logging.handlers``.


Formatter Objects
=================

``Formatter`` objects have the following attributes and methods. They
are responsible for converting a ``LogRecord`` to (usually) a string
which can be interpreted by either a human or an external system. The
base ``Formatter`` allows a formatting string to be specified. If none
is supplied, the default value of ``'%(message)s'`` is used.

A Formatter can be initialized with a format string which makes use of
knowledge of the ``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 ``LogRecord``'s *message*
attribute.  This format string contains standard Python %-style
mapping keys. See section *Old String Formatting Operations* for more
information on string formatting.

The useful mapping keys in a ``LogRecord`` are given in the section on
*LogRecord attributes*.

class class logging.Formatter(fmt=None, datefmt=None, style='%')

   Returns a new instance of the ``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.

   The *style* parameter can be one of '%', '{' or '$' and determines
   how the format string will be merged with its data: using one of
   %-formatting, ``str.format()`` or ``string.Template``.

   Changed in version 3.2: The *style* parameter was added.

   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)'``, ``formatTime()`` is called to format the event
      time. If there is exception information, it is formatted using
      ``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 ``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.

      If stack information is available, it's appended after the
      exception information, using ``formatStack()`` to transform it
      if necessary.

   formatTime(record, datefmt=None)

      This method should be called from ``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 ``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, ``time.localtime()`` is
      used; to change this for a particular formatter instance, set
      the ``converter`` attribute to a function with the same
      signature as ``time.localtime()`` or ``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.

   formatException(exc_info)

      Formats the specified exception information (a standard
      exception tuple as returned by ``sys.exc_info()``) as a string.
      This default implementation just uses
      ``traceback.print_exception()``. The resulting string is
      returned.

   formatStack(stack_info)

      Formats the specified stack information (a string as returned by
      ``traceback.print_stack()``, but with the last newline removed)
      as a string. This default implementation just returns the input
      value.


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 class logging.Filter(name='')

   Returns an instance of the ``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.

   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 whenever an event
is emitted by the handler, whereas filters attached to loggers are
consulted whenever an event is logged to the handler (using
``debug()``, ``info()``, etc.) 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.

Changed in version 3.2: You don't need to create specialized
``Filter`` classes, or use other classes with a ``filter`` method: you
can use a function (or other callable) as a filter. The filtering
logic will check to see if the filter object has a ``filter``
attribute: if it does, it's assumed to be a ``Filter`` and its
``filter()`` method is called. Otherwise, it's assumed to be a
callable and called with the record as the single parameter. The
returned value should conform to that returned by ``filter()``.

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 *Using
Filters to impart contextual information*).


LogRecord Objects
=================

``LogRecord`` instances are created automatically by the ``Logger``
every time something is logged, and can be created manually via
``makeLogRecord()`` (for example, from a pickled event received over
the wire).

class class logging.LogRecord(name, level, pathname, lineno, msg, args, exc_info, func=None, sinfo=None)

   Contains all the information pertinent to the event being logged.

   The primary information is passed in ``msg`` and ``args``, which
   are combined using ``msg % args`` to create the ``message`` field
   of the record.

   Parameters:
      * **name** -- The name of the logger used to log the event
        represented by this LogRecord.

      * **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.

      * **pathname** -- The full pathname of the source file where the
        logging call was made.

      * **lineno** -- The line number in the source file where the
        logging call was made.

      * **msg** -- The event description message, possibly a format
        string with placeholders for variable data.

      * **args** -- Variable data to merge into the *msg* argument to
        obtain the event description.

      * **exc_info** -- An exception tuple with the current exception
        information, or *None* if no exception information is
        available.

      * **func** -- The name of the function or method from which the
        logging call was invoked.

      * **sinfo** -- A text string representing stack information from
        the base of the stack in the current thread, up to the logging
        call.

   getMessage()

      Returns the message for this ``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, ``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.

   Changed in version 3.2: The creation of a ``LogRecord`` has been
   made more configurable by providing a factory which is used to
   create the record. The factory can be set using
   ``getLogRecordFactory()`` and ``setLogRecordFactory()`` (see this
   for the factory's signature).

   This functionality can be used to inject your own values into a
   LogRecord at creation time. You can use the following pattern:

      old_factory = logging.getLogRecordFactory()

      def record_factory(*args, **kwargs):
          record = old_factory(*args, **kwargs)
          record.custom_attribute = 0xdecafbad
          return record

      logging.setLogRecordFactory(record_factory)

   With this pattern, multiple factories could be chained, and as long
   as they don't overwrite each other's attributes or unintentionally
   overwrite the standard attributes listed above, there should be no
   surprises.


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.

If you are using {}-formatting (``str.format()``), you can use
``{attrname}`` as the placeholder in the format string. If you are
using $-formatting (``string.Template``), use the form
``${attrname}``. In both cases, of course, replace ``attrname`` with
the actual attribute name you want to use.

In the case of {}-formatting, you can specify formatting flags by
placing them after the attribute name, separated from it with a colon.
For example: a placeholder of ``{msecs:03d}`` would format a
millisecond value of ``4`` as ``004``. Refer to the ``str.format()``
documentation for full details on the options available to you.

+------------------+---------------------------+-------------------------------------------------+
| Attribute name   | Format                    | Description                                     |
+==================+===========================+=================================================+
| args             | You shouldn't need to     | The tuple of arguments merged into ``msg`` to   |
|                  | format this yourself.     | produce ``message``.                            |
+------------------+---------------------------+-------------------------------------------------+
| asctime          | ``%(asctime)s``           | Human-readable time when the ``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 ``LogRecord`` was created (as     |
|                  |                           | returned by ``time.time()``).                   |
+------------------+---------------------------+-------------------------------------------------+
| exc_info         | You shouldn't need to     | Exception tuple (à la ``sys.exc_info``) or, if  |
|                  | format this yourself.     | 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           |
|                  |                           | (``DEBUG``, ``INFO``, ``WARNING``, ``ERROR``,   |
|                  |                           | ``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        |
|                  |                           | ``LogRecord`` was created.                      |
+------------------+---------------------------+-------------------------------------------------+
| message          | ``%(message)s``           | The logged message, computed as ``msg % args``. |
|                  |                           | This is set when ``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 *Using |
|                  |                           | arbitrary objects as 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.                              |
+------------------+---------------------------+-------------------------------------------------+
| stack_info       | You shouldn't need to     | Stack frame information (where available) from  |
|                  | format this yourself.     | the bottom of the stack in the current thread,  |
|                  |                           | up to and including the stack frame of the      |
|                  |                           | logging call which resulted in the creation of  |
|                  |                           | this record.                                    |
+------------------+---------------------------+-------------------------------------------------+
| thread           | ``%(thread)d``            | Thread ID (if available).                       |
+------------------+---------------------------+-------------------------------------------------+
| threadName       | ``%(threadName)s``        | Thread name (if available).                     |
+------------------+---------------------------+-------------------------------------------------+


LoggerAdapter Objects
=====================

``LoggerAdapter`` instances are used to conveniently pass contextual
information into logging calls. For a usage example , see the section
on *adding contextual information to your logging output*.

class class logging.LoggerAdapter(logger, extra)

   Returns an instance of ``LoggerAdapter`` initialized with an
   underlying ``Logger`` instance and a dict-like object.

   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, ``LoggerAdapter`` supports the following
methods of ``Logger``, i.e. ``debug()``, ``info()``, ``warning()``,
``error()``, ``exception()``, ``critical()``, ``log()``,
``isEnabledFor()``, ``getEffectiveLevel()``, ``setLevel()``,
``hasHandlers()``. These methods have the same signatures as their
counterparts in ``Logger``, so you can use the two types of instances
interchangeably.

Changed in version 3.2: The ``isEnabledFor()``,
``getEffectiveLevel()``, ``setLevel()`` and ``hasHandlers()`` methods
were added to ``LoggerAdapter``.  These methods delegate 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
``signal`` module, you may not be able to use logging from within such
handlers. This is because lock implementations in the ``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.

logging.getLogger(name=None)

   Return a logger with the specified name or, if name is ``None``,
   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.

logging.getLoggerClass()

   Return either the standard ``Logger`` class, or the last class
   passed to ``setLoggerClass()``. This function may be called from
   within a new class definition, to ensure that installing a
   customised ``Logger`` class will not undo customisations already
   applied by other code. For example:

      class MyLogger(logging.getLoggerClass()):
          # ... override behaviour here

logging.getLogRecordFactory()

   Return a callable which is used to create a ``LogRecord``.

   New in version 3.2: This function has been provided, along with
   ``setLogRecordFactory()``, to allow developers more control over
   how the ``LogRecord`` representing a logging event is constructed.

   See ``setLogRecordFactory()`` for more information about the how
   the factory is called.

logging.debug(msg, *args, **kwargs)

   Logs a message with level ``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 three 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 ``sys.exc_info()``) is
   provided, it is used; otherwise, ``sys.exc_info()`` is called to
   get the exception information.

   The second optional keyword argument is *stack_info*, which
   defaults to False. If specified as True, stack information is added
   to the logging message, including the actual logging call. Note
   that this is not the same stack information as that displayed
   through specifying *exc_info*: The former is stack frames from the
   bottom of the stack up to the logging call in the current thread,
   whereas the latter is information about stack frames which have
   been unwound, following an exception, while searching for exception
   handlers.

   You can specify *stack_info* independently of *exc_info*, e.g. to
   just show how you got to a certain point in your code, even when no
   exceptions were raised. The stack frames are printed following a
   header line which says:

      Stack (most recent call last):

   This mimics the *Traceback (most recent call last):* which is used
   when displaying exception frames.

   The third 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 ``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
   ``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 ``Formatter``s would
   be used with particular ``Handler``s.

   New in version 3.2: The *stack_info* parameter was added.

logging.info(msg, *args, **kwargs)

   Logs a message with level ``INFO`` on the root logger. The
   arguments are interpreted as for ``debug()``.

logging.warning(msg, *args, **kwargs)

   Logs a message with level ``WARNING`` on the root logger. The
   arguments are interpreted as for ``debug()``.

logging.error(msg, *args, **kwargs)

   Logs a message with level ``ERROR`` on the root logger. The
   arguments are interpreted as for ``debug()``.

logging.critical(msg, *args, **kwargs)

   Logs a message with level ``CRITICAL`` on the root logger. The
   arguments are interpreted as for ``debug()``.

logging.exception(msg, *args)

   Logs a message with level ``ERROR`` on the root logger. The
   arguments are interpreted as for ``debug()``. Exception info is
   added to the logging message. This function should only be called
   from an exception handler.

logging.log(level, msg, *args, **kwargs)

   Logs a message with level *level* on the root logger. The other
   arguments are interpreted as for ``debug()``.

   PLEASE NOTE: The above module-level functions which delegate to the
   root logger 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. These
   convenience functions call ``basicConfig()`` to ensure that at
   least one handler is available; in earlier versions of Python, 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.

logging.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.

logging.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 ``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 *Custom Levels*.

logging.getLevelName(lvl)

   Returns the textual representation of logging level *lvl*. If the
   level is one of the predefined levels ``CRITICAL``, ``ERROR``,
   ``WARNING``, ``INFO`` or ``DEBUG`` then you get the corresponding
   string. If you have associated levels with names using
   ``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.

logging.makeLogRecord(attrdict)

   Creates and returns a new ``LogRecord`` instance whose attributes
   are defined by *attrdict*. This function is useful for taking a
   pickled ``LogRecord`` attribute dictionary, sent over a socket, and
   reconstituting it as a ``LogRecord`` instance at the receiving end.

logging.basicConfig(**kwargs)

   Does basic configuration for the logging system by creating a
   ``StreamHandler`` with a default ``Formatter`` and adding it to the
   root logger. The functions ``debug()``, ``info()``, ``warning()``,
   ``error()`` and ``critical()`` will call ``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.

   PLEASE 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.

   +----------------+-----------------------------------------------+
   | 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.           |
   +----------------+-----------------------------------------------+
   | ``style``      | If ``format`` is specified, use this style    |
   |                | for the format string. One of '%', '{' or '$' |
   |                | for %-formatting, ``str.format()`` or         |
   |                | ``string.Template`` respectively, and         |
   |                | defaulting to '%' if not specified.           |
   +----------------+-----------------------------------------------+
   | ``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.                 |
   +----------------+-----------------------------------------------+

   Changed in version 3.2: The ``style`` argument was added.

logging.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.

logging.setLoggerClass(klass)

   Tells the logging system to use the class *klass* when
   instantiating a logger. The class should define ``__init__()`` such
   that only a name argument is required, and the ``__init__()``
   should call ``Logger.__init__()``. This function is typically
   called before any loggers are instantiated by applications which
   need to use custom logger behavior.

logging.setLogRecordFactory(factory)

   Set a callable which is used to create a ``LogRecord``.

   Parameters:
      **factory** -- The factory callable to be used to instantiate a
      log record.

   New in version 3.2: This function has been provided, along with
   ``getLogRecordFactory()``, to allow developers more control over
   how the ``LogRecord`` representing a logging event is constructed.

   The factory has the following signature:

   ``factory(name, level, fn, lno, msg, args, exc_info, func=None,
   sinfo=None, **kwargs)``

      name:
         The logger name.

      level:
         The logging level (numeric).

      fn:
         The full pathname of the file where the logging call was
         made.

      lno:
         The line number in the file where the logging call was made.

      msg:
         The logging message.

      args:
         The arguments for the logging message.

      exc_info:
         An exception tuple, or None.

      func:
         The name of the function or method which invoked the logging
         call.

      sinfo:
         A stack traceback such as is provided by
         ``traceback.print_stack()``, showing the call hierarchy.

      kwargs:
         Additional keyword arguments.


Integration with the warnings module
====================================

The ``captureWarnings()`` function can be used to integrate
``logging`` with the ``warnings`` module.

logging.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 ``warnings``
   module will be redirected to the logging system. Specifically, a
   warning will be formatted using ``warnings.formatwarning()`` and
   the resulting string logged to a logger named 'py.warnings' with a
   severity of *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).

See also:

   Module ``logging.config``
      Configuration API for the logging module.

   Module ``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
      This is the original source for the ``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
      ``logging`` package in the standard library.
