16.6. "logging" — Logging facility for Python
*********************************************

**Source code:** Lib/logging/__init__.py


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.


16.6.1. 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 "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 logging.Logger

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.

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.

   See Logging Levels for a list of levels.

   Changed in version 3.2: The *lvl* parameter now accepts a string
   representation of the level such as ‘INFO’ as an alternative to the
   integer constants such as "INFO". Note, however, that levels are
   internally stored as integers, and methods such as e.g.
   "getEffectiveLevel()" and "isEnabledFor()" will return/expect to be
   passed integers.

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. The
   value returned is an integer, typically one of "logging.DEBUG",
   "logging.INFO" etc.

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*, *stack_info*, and *extra*.

   If *exc_info* does not evaluate as false, it causes exception
   information to be added to the logging message. If an exception
   tuple (in the format returned by "sys.exc_info()") or an exception
   instance 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 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.

   Changed in version 3.5: The *exc_info* parameter can now accept
   exception instances.

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()".

   Note: There is an obsolete method "warn" which is functionally
     identical to "warning". As "warn" is deprecated, please do not
     use it - use "warning" instead.

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, **kwargs)

   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. 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.

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.


16.6.2. 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               |
+----------------+-----------------+


16.6.3. 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).

   See Logging Levels for a list of levels.

   Changed in version 3.2: The *lvl* parameter now accepts a string
   representation of the level such as ‘INFO’ as an alternative to the
   integer constants such as "INFO".

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. 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.

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. 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).

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".


16.6.4. 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, 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 "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 printf-style String Formatting for more information on string
formatting.

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

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". See Using
   particular formatting styles throughout your application for more
   information on using {- and $-formatting for log messages.

   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.

      Changed in version 3.3: Previously, the default ISO 8601 format
      was hard-coded as in this example: "2010-09-06 22:38:15,292"
      where the part before the comma is handled by a strptime format
      string ("'%Y-%m-%d %H:%M:%S'"), and the part after the comma is
      a millisecond value. Because strptime does not have a format
      placeholder for milliseconds, the millisecond value is appended
      using another format string, "'%s,%03d'" — and both of these
      format strings have been hardcoded into this method. With the
      change, these strings are defined as class-level attributes
      which can be overridden at the instance level when desired. The
      names of the attributes are "default_time_format" (for the
      strptime format string) and "default_msec_format" (for appending
      the millisecond value).

   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.


16.6.5. 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 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 before an event
is emitted by the handler, whereas filters attached to loggers are
consulted whenever an event is logged (using "debug()", "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.

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).


16.6.6. 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 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. Note that this name will always
        have this value, even though it may be emitted by a handler
        attached to a different (ancestor) logger.

      * **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.


16.6.7. 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", 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 "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 no |
|                  | format this yourself.     | 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).                     |
+------------------+---------------------------+-------------------------------------------------+

Changed in version 3.1: *processName* was added.


16.6.8. 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 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": "debug()", "info()", "warning()", "error()",
"exception()", "critical()", "log()", "isEnabledFor()",
"getEffectiveLevel()", "setLevel()" and "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.


16.6.9. 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.


16.6.10. 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 customized
   "Logger" class will not undo customizations 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 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()".

   Note: There is an obsolete function "warn" which is functionally
     identical to "warning". As "warn" is deprecated, please do not
     use it - use "warning" instead.

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, **kwargs)

   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()".

   Note: The above module-level convenience functions, which
     delegate to the root logger, call "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 "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.

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. 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.

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.

   Note: Levels are internally integers (as they need to be compared
     in the logging logic). 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
     LogRecord attributes).

   Changed in version 3.4: In Python versions earlier than 3.4, this
   function could also be passed a text level, and would return the
   corresponding numeric value of the level. This undocumented
   behaviour was considered a mistake, and was removed in Python 3.4,
   but reinstated in 3.4.2 due to retain backward compatibility.

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.

   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, a "ValueError" is raised.            |
   +----------------+-----------------------------------------------+
   | "handlers"     | If specified, this should be an iterable of   |
   |                | already created handlers to add to the root   |
   |                | logger. Any handlers which don’t already have |
   |                | a formatter set will be assigned the default  |
   |                | formatter created in this function. Note that |
   |                | this argument is incompatible with ‘filename’ |
   |                | or ‘stream’ - if both are present, a          |
   |                | "ValueError" is raised.                       |
   +----------------+-----------------------------------------------+

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

   Changed in version 3.3: The "handlers" argument was added.
   Additional checks were added to catch situations where incompatible
   arguments are specified (e.g. "handlers" together with "stream" or
   "filename", or "stream" together with "filename").

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.


16.6.11. Module-Level Attributes
================================

logging.lastResort

   A “handler of last resort” is available through this attribute.
   This is a "StreamHandler" writing to "sys.stderr" with a level of
   "WARNING", and is used to handle logging events in the absence of
   any logging configuration. The end result is to just print the
   message to "sys.stderr". This replaces the earlier error message
   saying that “no handlers could be found for logger XYZ”. If you
   need the earlier behaviour for some reason, "lastResort" can be set
   to "None".

   New in version 3.2.


16.6.12. 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.
