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📛 NAME

logging

🚀 Quick Reference

Use Case	Command	Description
📝 Basic console logging	logging.basicConfig(level=logging.INFO)	Configure root logger to print to stderr with default format
📁 Log to file	logging.basicConfig(filename='app.log', level=logging.DEBUG)	Write log messages to a file
🏷️ Get a logger	logger = logging.getLogger(__name__)	Retrieve or create a logger for the current module
🖨️ Log messages	logger.debug('debug') logger.info('info') logger.warning('warning') logger.error('error') logger.critical('critical')	Log messages at different severity levels
⚠️ Exception logging	logging.exception('Exception occurred')	Log an error with traceback information
🎨 Custom format	logging.basicConfig(format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')	Set a custom log record format
🔢 Get level name	logging.getLevelName(logging.DEBUG)	Returns 'DEBUG'
🚫 Disable logging	logging.disable(logging.CRITICAL)	Suppress all messages at or below the specified level
➕ Add a handler	logger.addHandler(logging.FileHandler('debug.log'))	Attach a file handler to a logger
🔌 LoggerAdapter	adapter = logging.LoggerAdapter(logger, {'user': 'john'})	Add contextual info to log messages

📚 MODULE REFERENCE

https://docs.python.org/3.10/library/logging.html

The following documentation is automatically generated from the Python source files. It may be incomplete, incorrect or include features that are considered implementation detail and may vary between Python implementations. When in doubt, consult the module reference at the location listed above.

📖 DESCRIPTION

Logging package for Python. Based on PEP 282 and comments thereto in comp.lang.python.

Copyright (C) 2001-2019 Vinay Sajip. All Rights Reserved.

To use, simply import logging and log away!

📦 PACKAGE CONTENTS

• config
• handlers

🏛️ CLASSES

builtins.object

• BufferingFormatter
• Filter
• Formatter
• LogRecord
• LoggerAdapter

Filterer(builtins.object)

• Handler
  • NullHandler
  • StreamHandler
    • FileHandler
• Logger

🔧 class BufferingFormatter(builtins.object)

BufferingFormatter(linefmt=None)

A formatter suitable for formatting a number of records.

Methods defined here:

• __init__(self, linefmt=None)
  Optionally specify a formatter which will be used to format each individual record.
• format(self, records)
  Format the specified records and return the result as a string.
• formatFooter(self, records)
  Return the footer string for the specified records.
• formatHeader(self, records)
  Return the header string for the specified records.

Data descriptors defined here:

• __dict__ — dictionary for instance variables (if defined)
• __weakref__ — list of weak references to the object (if defined)

📄 class FileHandler(StreamHandler)

FileHandler(filename, mode='a', encoding=None, delay=False, errors=None)

A handler class which writes formatted logging records to disk files.

Method resolution order:

FileHandler
StreamHandler
Handler
Filterer
builtins.object

Methods defined here:

• __init__(self, filename, mode='a', encoding=None, delay=False, errors=None)
  Open the specified file and use it as the stream for logging.
• __repr__(self)
  Return repr(self).
• close(self)
  Closes the stream.
• emit(self, record)
  Emit a record. If the stream was not opened because 'delay' was specified in the constructor, open it before calling the superclass's emit. If stream is not open, current mode is 'w' and _closed=True, record will not be emitted (see Issue #42378).

Methods inherited from StreamHandler: flush, setStream

Data inherited from StreamHandler: terminator = '\n'

Methods inherited from Handler: acquire, createLock, format, get_name, handle, handleError, release, setFormatter, setLevel, set_name

Data descriptors inherited from Handler: name

Methods inherited from Filterer: addFilter, filter, removeFilter

Data descriptors inherited from Filterer: __dict__, __weakref__

🎛️ class Filter(builtins.object)

Filter(name='')

Filter instances are used to perform arbitrary filtering of LogRecords. Loggers and Handlers can optionally use Filter instances to filter records as desired. 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.

Methods defined here:

• __init__(self, name='')
  Initialize a filter. Initialize with the name of the logger which, together with its children, will have its events allowed through the filter. If no name is specified, allow every event.
• filter(self, record)
  Determine if the specified record is to be logged. Returns True if the record should be logged, or False otherwise. If deemed appropriate, the record may be modified in-place.

Data descriptors defined here:

• __dict__ — dictionary for instance variables (if defined)
• __weakref__ — list of weak references to the object (if defined)

📝 class Formatter(builtins.object)

Formatter(fmt=None, datefmt=None, style='%', validate=True, *, defaults=None)

Formatter instances are used to convert a LogRecord to text. Formatters need to know how a LogRecord is constructed. 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 style-dependent default value, "%(message)s", "{message}", or "${message}", is used.

The Formatter can be initialized with a format string which makes use of knowledge of the LogRecord attributes. Currently, the useful attributes in a LogRecord are:

• %(name)s — Name of the logger (logging channel)
• %(levelno)s — Numeric logging level for the message (DEBUG, INFO, WARNING, ERROR, CRITICAL)
• %(levelname)s — Text logging level for the message
• %(pathname)s — Full pathname of the source file where the logging call was issued (if available)
• %(filename)s — Filename portion of pathname
• %(module)s — Module (name portion of filename)
• %(lineno)d — Source line number where the logging call was issued (if available)
• %(funcName)s — Function name
• %(created)f — Time when the LogRecord was created (time.time() return value)
• %(asctime)s — Textual time when the LogRecord was created
• %(msecs)d — Millisecond portion of the creation time
• %(relativeCreated)d — Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded
• %(thread)d — Thread ID (if available)
• %(threadName)s — Thread name (if available)
• %(process)d — Process ID (if available)
• %(message)s — The result of record.getMessage(), computed just as the record is emitted

Methods defined here:

• __init__(self, fmt=None, datefmt=None, style='%', validate=True, *, defaults=None)
  Initialize the formatter with specified format strings. Allow for specialized date formatting with the optional datefmt argument. If datefmt is omitted, you get an ISO8601-like (or RFC 3339-like) format. Use a style parameter of '%', '{' or '$' to specify formatting style.
• format(self, record)
  Format the specified record as text.
• formatException(self, ei)
  Format and return the specified exception information as a string. Uses traceback.print_exception().
• formatMessage(self, record)
• formatStack(self, stack_info)
  Extension point for specialized formatting of stack information. The base implementation returns the value passed in.
• formatTime(self, record, datefmt=None)
  Return the creation time of the specified LogRecord as formatted text. The converter attribute can be set to a function like time.localtime() or time.gmtime().
• usesTime(self)
  Check if the format uses the creation time of the record.

Static methods defined here:

• converter = localtime(...)
  Convert seconds since the Epoch to a time tuple expressing local time.

Data descriptors defined here:

• __dict__ — dictionary for instance variables (if defined)
• __weakref__ — list of weak references to the object (if defined)

Data and other attributes:

• default_msec_format = '%s,%03d'
• default_time_format = '%Y-%m-%d %H:%M:%S'

⚙️ class Handler(Filterer)

Handler(level=0)

Handler instances dispatch logging events to specific destinations. The base handler class. Acts as a placeholder which defines the Handler interface. Handlers can optionally use Formatter instances to format records as desired. By default, no formatter is specified; in this case, the 'raw' message as determined by record.message is logged.

Method resolution order:

Handler
Filterer
builtins.object

Methods defined here:

• __init__(self, level=0)
  Initializes the instance - basically setting the formatter to None and the filter list to empty.
• __repr__(self)
  Return repr(self).
• acquire(self)
  Acquire the I/O thread lock.
• close(self)
  Tidy up any resources used by the handler. This version removes the handler from an internal map of handlers, _handlers, which is used for handler lookup by name. Subclasses should ensure that this gets called from overridden close() methods.
• createLock(self)
  Acquire a thread lock for serializing access to the underlying I/O.
• emit(self, 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.
• flush(self)
  Ensure all logging output has been flushed. This version does nothing and is intended to be implemented by subclasses.
• format(self, record)
  Format the specified record. If a formatter is set, use it. Otherwise, use the default formatter for the module.
• get_name(self)
• handle(self, record)
  Conditionally emit the specified logging record. Emission depends on filters which may have been added to the handler. Wrap the actual emission of the record with acquisition/release of the I/O thread lock. Returns whether the filter passed the record for emission.
• handleError(self, record)
  Handle errors which occur during an emit() call. If raiseExceptions is false, exceptions get silently ignored.
• release(self)
  Release the I/O thread lock.
• setFormatter(self, fmt)
  Set the formatter for this handler.
• setLevel(self, level)
  Set the logging level of this handler. level must be an int or a str.
• set_name(self, name)

Data descriptors defined here: name

Methods inherited from Filterer: addFilter, filter, removeFilter

Data descriptors inherited from Filterer: __dict__, __weakref__

📋 class LogRecord(builtins.object)

LogRecord(name, level, pathname, lineno, msg, args, exc_info, func=None, sinfo=None, **kwargs)

A LogRecord instance represents an event being logged. LogRecord instances are created every time something is logged. They contain all the information pertinent to the event being logged. The main information passed in is in msg and args, which are combined using str(msg) % args to create the message field of the record. The record also includes information such as when the record was created, the source line where the logging call was made, and any exception information to be logged.

Methods defined here:

• __init__(self, name, level, pathname, lineno, msg, args, exc_info, func=None, sinfo=None, **kwargs)
  Initialize a logging record with interesting information.
• __repr__(self)
  Return repr(self).
• getMessage(self)
  Return the message for this LogRecord after merging any user-supplied arguments with the message.

Data descriptors defined here:

• __dict__ — dictionary for instance variables (if defined)
• __weakref__ — list of weak references to the object (if defined)

📢 class Logger(Filterer)

Logger(name, level=0)

Instances of the Logger class represent a single logging channel. A "logging channel" indicates an area of an application. Exactly how an "area" is defined is up to the application developer. Since an application can have any number of areas, logging channels are identified by a unique string. Application areas can be nested (e.g. an area of "input processing" might include sub-areas "read CSV files", "read XLS files" and "read Gnumeric files"). To cater for this natural nesting, channel names are organized into a namespace hierarchy where levels are separated by periods, much like the Java or Python package namespace. There is no arbitrary limit to the depth of nesting.

Method resolution order:

Logger
Filterer
builtins.object

Methods defined here:

• __init__(self, name, level=0)
  Initialize the logger with a name and an optional level.
• __reduce__(self)
  Helper for pickle.
• __repr__(self)
  Return repr(self).
• addHandler(self, hdlr)
  Add the specified handler to this logger.
• callHandlers(self, record)
  Pass a record to all relevant handlers. Loop through all handlers for this logger and its parents in the logger hierarchy. If no handler was found, output a one-off error message to sys.stderr. Stop searching up the hierarchy whenever a logger with the "propagate" attribute set to zero is found.
• critical(self, msg, *args, **kwargs)
  Log msg % args with severity 'CRITICAL'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.critical("Houston, we have a %s", "major disaster", exc_info=1)
• debug(self, msg, *args, **kwargs)
  Log msg % args with severity 'DEBUG'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.debug("Houston, we have a %s", "thorny problem", exc_info=1)
• error(self, msg, *args, **kwargs)
  Log msg % args with severity 'ERROR'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.error("Houston, we have a %s", "major problem", exc_info=1)
• exception(self, msg, *args, exc_info=True, **kwargs)
  Convenience method for logging an ERROR with exception information.
• fatal(self, msg, *args, **kwargs)
  Don't use this method, use critical() instead.
• findCaller(self, stack_info=False, stacklevel=1)
  Find the stack frame of the caller so that we can note the source file name, line number and function name.
• getChild(self, suffix)
  Get a logger which is a descendant to this one. logging.getLogger('abc').getChild('def.ghi') is the same as logging.getLogger('abc.def.ghi'). It's useful, for example, when the parent logger is named using __name__ rather than a literal string.
• getEffectiveLevel(self)
  Get the effective level for this logger. Loop through this logger and its parents in the logger hierarchy, looking for a non-zero logging level. Return the first one found.
• handle(self, record)
  Call the handlers for the specified record. This method is used for unpickled records received from a socket, as well as those created locally. Logger-level filtering is applied.
• hasHandlers(self)
  See if this logger has any handlers configured. Loop through all handlers for this logger and its parents in the logger hierarchy. Return True if a handler was found, else False. Stop searching up the hierarchy whenever a logger with the "propagate" attribute set to zero is found.
• info(self, msg, *args, **kwargs)
  Log msg % args with severity 'INFO'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.info("Houston, we have a %s", "interesting problem", exc_info=1)
• isEnabledFor(self, level)
  Is this logger enabled for level 'level'?
• log(self, level, msg, *args, **kwargs)
  Log msg % args with the integer severity 'level'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.log(level, "We have a %s", "mysterious problem", exc_info=1)
• makeRecord(self, name, level, fn, lno, msg, args, exc_info, func=None, extra=None, sinfo=None)
  A factory method which can be overridden in subclasses to create specialized LogRecords.
• removeHandler(self, hdlr)
  Remove the specified handler from this logger.
• setLevel(self, level)
  Set the logging level of this logger. level must be an int or a str.
• warn(self, msg, *args, **kwargs)
• warning(self, msg, *args, **kwargs)
  Log msg % args with severity 'WARNING'. To pass exception information, use the keyword argument exc_info with a true value, e.g. logger.warning("Houston, we have a %s", "bit of a problem", exc_info=1)

Data and other attributes: manager = <logging.Manager object>, root = <RootLogger root (WARNING)>

Methods inherited from Filterer: addFilter, filter, removeFilter

Data descriptors inherited from Filterer: __dict__, __weakref__

🔌 class LoggerAdapter(builtins.object)

LoggerAdapter(logger, extra=None)

An adapter for loggers which makes it easier to specify contextual information in logging output.

Methods defined here:

• __init__(self, logger, extra=None)
  Initialize the adapter with a logger and a dict-like object which provides contextual information. This constructor signature allows easy stacking of LoggerAdapters, if so desired. You can effectively pass keyword arguments as shown in the following example: adapter = LoggerAdapter(someLogger, dict(p1=v1, p2="v2"))
• __repr__(self)
  Return repr(self).
• critical(self, msg, *args, **kwargs)
  Delegate a critical call to the underlying logger.
• debug(self, msg, *args, **kwargs)
  Delegate a debug call to the underlying logger.
• error(self, msg, *args, **kwargs)
  Delegate an error call to the underlying logger.
• exception(self, msg, *args, exc_info=True, **kwargs)
  Delegate an exception call to the underlying logger.
• getEffectiveLevel(self)
  Get the effective level for the underlying logger.
• hasHandlers(self)
  See if the underlying logger has any handlers.
• info(self, msg, *args, **kwargs)
  Delegate an info call to the underlying logger.
• isEnabledFor(self, level)
  Is this logger enabled for level 'level'?
• log(self, level, msg, *args, **kwargs)
  Delegate a log call to the underlying logger, after adding contextual information from this adapter instance.
• process(self, msg, kwargs)
  Process the logging message and keyword arguments passed in to a logging call to insert contextual information. You can either manipulate the message itself, the keyword args or both. Return the message and kwargs modified (or not) to suit your needs. Normally, you'll only need to override this one method in a LoggerAdapter subclass for your specific needs.
• setLevel(self, level)
  Set the specified level on the underlying logger.
• warn(self, msg, *args, **kwargs)
• warning(self, msg, *args, **kwargs)
  Delegate a warning call to the underlying logger.

Readonly properties: name

Data descriptors: __dict__, __weakref__, manager

🚫 class NullHandler(Handler)

NullHandler(level=0)

This handler does nothing. It's intended to be used to avoid the "No handlers could be found for logger XXX" one-off warning. This is important for library code, which may contain code to log events. If a user of the library does not configure logging, the one-off warning might be produced; to avoid this, the library developer simply needs to instantiate a NullHandler and add it to the top-level logger of the library module or package.

Method resolution order:

NullHandler
Handler
Filterer
builtins.object

Methods defined here:

• createLock(self)
  Acquire a thread lock for serializing access to the underlying I/O.
• emit(self, record)
  Stub.
• handle(self, record)
  Stub.

Methods inherited from Handler: __init__, __repr__, acquire, close, flush, format, get_name, handleError, release, setFormatter, setLevel, set_name

Data descriptors inherited from Handler: name

Methods inherited from Filterer: addFilter, filter, removeFilter

Data descriptors inherited from Filterer: __dict__, __weakref__

🌊 class StreamHandler(Handler)

StreamHandler(stream=None)

A handler class which writes logging records, appropriately formatted, to a stream. Note that this class does not close the stream, as sys.stdout or sys.stderr may be used.

Method resolution order:

StreamHandler
Handler
Filterer
builtins.object

Methods defined here:

• __init__(self, stream=None)
  Initialize the handler. If stream is not specified, sys.stderr is used.
• __repr__(self)
  Return repr(self).
• emit(self, record)
  Emit a record. If a formatter is specified, it is used to format the record. The record is then written to the stream with a trailing newline. If exception information is present, it is formatted using traceback.print_exception and appended to the stream.
• flush(self)
  Flushes the stream.
• setStream(self, stream)
  Sets the StreamHandler's stream to the specified value, if it is different. Returns the old stream, if the stream was changed, or None if it wasn't.

Data and other attributes: terminator = '\n'

Methods inherited from Handler: acquire, close, createLock, format, get_name, handle, handleError, release, setFormatter, setLevel, set_name

Data descriptors inherited from Handler: name

Methods inherited from Filterer: addFilter, filter, removeFilter

Data descriptors inherited from Filterer: __dict__, __weakref__

⚙️ FUNCTIONS

addLevelName(level, levelName)
Associate 'levelName' with 'level'. This is used when converting levels to text during message formatting.

basicConfig(**kwargs)
Do basic configuration for the logging system. This function does nothing if the root logger already has handlers configured, unless the keyword argument force is set to True. It is a convenience method intended for use by simple scripts to do one-shot configuration of the logging package.

The default behaviour is to create a StreamHandler which writes to sys.stderr, set a formatter using the BASIC_FORMAT format string, and add the handler to the root logger. A number of optional keyword arguments may be specified:

• 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 a format string is specified, use this to specify the type of format string (possible values '%', '{', '$', defaults to '%').
• 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.
• handlers — If specified, this should be an iterable of already created handlers, which will be added to the root handler. Any handler in the list which does not have a formatter assigned will be assigned the formatter created in this function.
• force — If this keyword is specified as true, any existing handlers attached to the root logger are removed and closed, before carrying out the configuration as specified by the other arguments.
• encoding — If specified together with a filename, this encoding is passed to the created FileHandler, causing it to be used when the file is opened.
• errors — If specified together with a filename, this value is passed to the created FileHandler, causing it to be used when the file is opened in text mode. If not specified, the default value is backslashreplace.

Note that you could specify a stream created using open(filename, mode) rather than passing the filename and mode in. However, StreamHandler does not close its stream (since it may be using sys.stdout or sys.stderr), whereas FileHandler closes its stream when the handler is closed.

.. versionchanged:: 3.2 Added the style parameter.

.. versionchanged:: 3.3 Added the handlers parameter. A ValueError is now thrown for incompatible arguments.

.. versionchanged:: 3.8 Added the force parameter.

.. versionchanged:: 3.9 Added the encoding and errors parameters.

captureWarnings(capture)
If capture is true, redirect all warnings to the logging package. If capture is False, ensure that warnings are not redirected to logging but to their original destinations.

critical(msg, *args, **kwargs)
Log a message with severity 'CRITICAL' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

debug(msg, *args, **kwargs)
Log a message with severity 'DEBUG' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

disable(level=50)
Disable all logging calls of severity 'level' and below.

error(msg, *args, **kwargs)
Log a message with severity 'ERROR' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

exception(msg, *args, exc_info=True, **kwargs)
Log a message with severity 'ERROR' on the root logger, with exception information. If the logger has no handlers, basicConfig() is called to add a console handler with a pre-defined format.

fatal(msg, *args, **kwargs)
Don't use this function, use critical() instead.

getLevelName(level)
Return the textual or numeric representation of logging level 'level'. If the level is one of the predefined levels (CRITICAL, ERROR, WARNING, INFO, DEBUG) then you get the corresponding string. If you have associated levels with names using addLevelName then the name you have associated with 'level' is returned. If a numeric value corresponding to one of the defined levels is passed in, the corresponding string representation is returned. If a string representation of the level is passed in, the corresponding numeric value is returned. If no matching numeric or string value is passed in, the string 'Level %s' % level is returned.

getLogRecordFactory()
Return the factory to be used when instantiating a log record.

getLogger(name=None)
Return a logger with the specified name, creating it if necessary. If no name is specified, return the root logger.

getLoggerClass()
Return the class to be used when instantiating a logger.

info(msg, *args, **kwargs)
Log a message with severity 'INFO' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

log(level, msg, *args, **kwargs)
Log msg % args with the integer severity 'level' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

makeLogRecord(dict)
Make a LogRecord whose attributes are defined by the specified dictionary. This function is useful for converting a logging event received over a socket connection (which is sent as a dictionary) into a LogRecord instance.

setLogRecordFactory(factory)
Set the factory to be used when instantiating a log record.

:param factory: A callable which will be called to instantiate a log record.

setLoggerClass(klass)
Set the class to be used when instantiating a logger. The class should define __init__() such that only a name argument is required, and the __init__() should call Logger.__init__().

shutdown(handlerList=[<weakref at 0x7ff8732be390; to '_StderrHandler' at 0x7ff8732cc4c0>])
Perform any cleanup actions in the logging system (e.g. flushing buffers). Should be called at application exit.

warn(msg, *args, **kwargs)

warning(msg, *args, **kwargs)
Log a message with severity 'WARNING' on the root logger. If the logger has no handlers, call basicConfig() to add a console handler with a pre-defined format.

📊 DATA

• BASIC_FORMAT = '%(levelname)s:%(name)s:%(message)s'
• CRITICAL = 50
• DEBUG = 10
• ERROR = 40
• FATAL = 50
• INFO = 20
• NOTSET = 0
• WARN = 30
• WARNING = 30
• __all__ = ['BASIC_FORMAT', 'BufferingFormatter', 'CRITICAL', 'DEBUG', ...
• __status__ = 'production'
• lastResort = <_StderrHandler <stderr> (WARNING)>
• raiseExceptions = True

ℹ️ VERSION

0.5.1.2

📅 DATE

07 February 2010

👤 AUTHOR

Vinay Sajip <vinay_sajip AT red-dove.com>

📁 FILE

/usr/lib/python3.10/logging/__init__.py

📛 NAME 🚀 Quick Reference 📚 MODULE REFERENCE 📖 DESCRIPTION 📦 PACKAGE CONTENTS 🏛️ CLASSES ⚙️ FUNCTIONS 📊 DATA ℹ️ VERSION 📅 DATE 👤 AUTHOR 📁 FILE