class logging.Formatter(fmt=None, datefmt=None, style='%', validate=True)
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, a format is used which is described in the formatTime() documentation. 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. This only applies to the format string fmt (e.g. '%(message)s' or {message}), not to the actual log messages passed to Logger.debug etc; 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.   Changed in version 3.8: The validate parameter was added. Incorrect or mismatched style and fmt will raise a ValueError. For example: logging.Formatter('%(asctime)s - %(message)s', style='{').
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 format ‘%Y-%m-%d %H:%M:%S,uuu’ is used, where the uuu part is a millisecond value and the other letters are as per the time.strftime() documentation. An example time in this format is 2003-01-23 00:29:50,411. 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 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).   Changed in version 3.9: The default_msec_format can be None.

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.


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.


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.


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 format ‘%Y-%m-%d %H:%M:%S,uuu’ is used, where the uuu part is a millisecond value and the other letters are as per the time.strftime() documentation. An example time in this format is 2003-01-23 00:29:50,411. 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 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).   Changed in version 3.9: The default_msec_format can be None.


logging.getLevelName(level)
Returns the textual or numeric representation of logging level level. If 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 level is returned. If a numeric value corresponding to one of the defined levels is passed in, the corresponding string representation is returned. The level parameter also accepts a string representation of the level such as ‘INFO’. In such cases, this functions returns the corresponding numeric value of the level. If no matching numeric or string value is passed in, the string ‘Level %s’ % level 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), and vice versa.   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.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.


class logging.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.

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

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

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

setLevel(level)
Sets the threshold for this handler to level. Logging messages which are less severe than level 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 level parameter now accepts a string representation of the level such as ‘INFO’ as an alternative to the integer constants such as INFO.

setFormatter(fmt)
Sets the Formatter for this handler to fmt.

addFilter(filter)
Adds the specified filter filter to this handler.

removeFilter(filter)
Removes the specified filter filter from this handler.

filter(record)
Apply this handler’s filters to the record and return True 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.

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

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.

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.

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).

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

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.


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


addFilter(filter)
Adds the specified filter filter to this 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.


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


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.


filter(record)
Apply this handler’s filters to the record and return True 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.


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


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


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.


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).


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


removeFilter(filter)
Removes the specified filter filter from this handler.


setFormatter(fmt)
Sets the Formatter for this handler to fmt.


setLevel(level)
Sets the threshold for this handler to level. Logging messages which are less severe than level 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 level parameter now accepts a string representation of the level such as ‘INFO’ as an alternative to the integer constants such as INFO.


__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.


logging.handlers — Logging handlers Source code: Lib/logging/handlers.py  Important This page contains only reference information. For tutorials, please see  Basic Tutorial Advanced Tutorial Logging Cookbook   The following useful handlers are provided in the package. Note that three of the handlers (StreamHandler, FileHandler and NullHandler) are actually defined in the logging module itself, but have been documented here along with the other handlers. StreamHandler The StreamHandler class, located in the core logging package, sends logging output to streams such as sys.stdout, sys.stderr or any file-like object (or, more precisely, any object which supports write() and flush() methods).
class logging.StreamHandler(stream=None)
Returns a new instance of the StreamHandler class. If stream is specified, the instance will use it for logging output; otherwise, sys.stderr will be used.
emit(record)
If a formatter is specified, it is used to format the record. The record is then written to the stream followed by terminator. If exception information is present, it is formatted using traceback.print_exception() and appended to the stream.

flush()
Flushes the stream by calling its flush() method. Note that the close() method is inherited from Handler and so does no output, so an explicit flush() call may be needed at times.

setStream(stream)
Sets the instance’s stream to the specified value, if it is different. The old stream is flushed before the new stream is set.  Parameters
stream – The stream that the handler should use.  Returns
the old stream, if the stream was changed, or None if it wasn’t.    New in version 3.7.

terminator
String used as the terminator when writing a formatted record to a stream. Default value is '\n'. If you don’t want a newline termination, you can set the handler instance’s terminator attribute to the empty string. In earlier versions, the terminator was hardcoded as '\n'.  New in version 3.2.

 FileHandler The FileHandler class, located in the core logging package, sends logging output to a disk file. It inherits the output functionality from StreamHandler.
class logging.FileHandler(filename, mode='a', encoding=None, delay=False, errors=None)
Returns a new instance of the FileHandler class. The specified file is opened and used as the stream for logging. If mode is not specified, 'a' is used. If encoding is not None, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call to emit(). By default, the file grows indefinitely. If errors is specified, it’s used to determine how encoding errors are handled.  Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
close()
Closes the file.

emit(record)
Outputs the record to the file.

 NullHandler  New in version 3.1.  The NullHandler class, located in the core logging package, does not do any formatting or output. It is essentially a ‘no-op’ handler for use by library developers.
class logging.NullHandler
Returns a new instance of the NullHandler class.
emit(record)
This method does nothing.

handle(record)
This method does nothing.

createLock()
This method returns None for the lock, since there is no underlying I/O to which access needs to be serialized.

 See Configuring Logging for a Library for more information on how to use NullHandler. WatchedFileHandler The WatchedFileHandler class, located in the logging.handlers module, is a FileHandler which watches the file it is logging to. If the file changes, it is closed and reopened using the file name. A file change can happen because of usage of programs such as newsyslog and logrotate which perform log file rotation. This handler, intended for use under Unix/Linux, watches the file to see if it has changed since the last emit. (A file is deemed to have changed if its device or inode have changed.) If the file has changed, the old file stream is closed, and the file opened to get a new stream. This handler is not appropriate for use under Windows, because under Windows open log files cannot be moved or renamed - logging opens the files with exclusive locks - and so there is no need for such a handler. Furthermore, ST_INO is not supported under Windows; stat() always returns zero for this value.
class logging.handlers.WatchedFileHandler(filename, mode='a', encoding=None, delay=False, errors=None)
Returns a new instance of the WatchedFileHandler class. The specified file is opened and used as the stream for logging. If mode is not specified, 'a' is used. If encoding is not None, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call to emit(). By default, the file grows indefinitely. If errors is provided, it determines how encoding errors are handled.  Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
reopenIfNeeded()
Checks to see if the file has changed. If it has, the existing stream is flushed and closed and the file opened again, typically as a precursor to outputting the record to the file.  New in version 3.6.

emit(record)
Outputs the record to the file, but first calls reopenIfNeeded() to reopen the file if it has changed.

 BaseRotatingHandler The BaseRotatingHandler class, located in the logging.handlers module, is the base class for the rotating file handlers, RotatingFileHandler and TimedRotatingFileHandler. You should not need to instantiate this class, but it has attributes and methods you may need to override.
class logging.handlers.BaseRotatingHandler(filename, mode, encoding=None, delay=False, errors=None)
The parameters are as for FileHandler. The attributes are:
namer
If this attribute is set to a callable, the rotation_filename() method delegates to this callable. The parameters passed to the callable are those passed to rotation_filename().  Note The namer function is called quite a few times during rollover, so it should be as simple and as fast as possible. It should also return the same output every time for a given input, otherwise the rollover behaviour may not work as expected.   New in version 3.3.

rotator
If this attribute is set to a callable, the rotate() method delegates to this callable. The parameters passed to the callable are those passed to rotate().  New in version 3.3.

rotation_filename(default_name)
Modify the filename of a log file when rotating. This is provided so that a custom filename can be provided. The default implementation calls the ‘namer’ attribute of the handler, if it’s callable, passing the default name to it. If the attribute isn’t callable (the default is None), the name is returned unchanged.  Parameters
default_name – The default name for the log file.    New in version 3.3.

rotate(source, dest)
When rotating, rotate the current log. The default implementation calls the ‘rotator’ attribute of the handler, if it’s callable, passing the source and dest arguments to it. If the attribute isn’t callable (the default is None), the source is simply renamed to the destination.  Parameters

source – The source filename. This is normally the base filename, e.g. ‘test.log’.
dest – The destination filename. This is normally what the source is rotated to, e.g. ‘test.log.1’.     New in version 3.3.

 The reason the attributes exist is to save you having to subclass - you can use the same callables for instances of RotatingFileHandler and TimedRotatingFileHandler. If either the namer or rotator callable raises an exception, this will be handled in the same way as any other exception during an emit() call, i.e. via the handleError() method of the handler. If you need to make more significant changes to rotation processing, you can override the methods. For an example, see Using a rotator and namer to customize log rotation processing. RotatingFileHandler The RotatingFileHandler class, located in the logging.handlers module, supports rotation of disk log files.
class logging.handlers.RotatingFileHandler(filename, mode='a', maxBytes=0, backupCount=0, encoding=None, delay=False, errors=None)
Returns a new instance of the RotatingFileHandler class. The specified file is opened and used as the stream for logging. If mode is not specified, 'a' is used. If encoding is not None, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call to emit(). By default, the file grows indefinitely. If errors is provided, it determines how encoding errors are handled. You can use the maxBytes and backupCount values to allow the file to rollover at a predetermined size. When the size is about to be exceeded, the file is closed and a new file is silently opened for output. Rollover occurs whenever the current log file is nearly maxBytes in length; but if either of maxBytes or backupCount is zero, rollover never occurs, so you generally want to set backupCount to at least 1, and have a non-zero maxBytes. When backupCount is non-zero, the system will save old log files by appending the extensions ‘.1’, ‘.2’ etc., to the filename. For example, with a backupCount of 5 and a base file name of app.log, you would get app.log, app.log.1, app.log.2, up to app.log.5. The file being written to is always app.log. When this file is filled, it is closed and renamed to app.log.1, and if files app.log.1, app.log.2, etc. exist, then they are renamed to app.log.2, app.log.3 etc. respectively.  Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
doRollover()
Does a rollover, as described above.

emit(record)
Outputs the record to the file, catering for rollover as described previously.

 TimedRotatingFileHandler The TimedRotatingFileHandler class, located in the logging.handlers module, supports rotation of disk log files at certain timed intervals.
class logging.handlers.TimedRotatingFileHandler(filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False, atTime=None, errors=None)
Returns a new instance of the TimedRotatingFileHandler class. The specified file is opened and used as the stream for logging. On rotating it also sets the filename suffix. Rotating happens based on the product of when and interval. You can use the when to specify the type of interval. The list of possible values is below. Note that they are not case sensitive.
Value Type of interval If/how atTime is used
'S' Seconds Ignored
'M' Minutes Ignored
'H' Hours Ignored
'D' Days Ignored
'W0'-'W6' Weekday (0=Monday) Used to compute initial rollover time
'midnight' Roll over at midnight, if atTime not specified, else at time atTime Used to compute initial rollover time   When using weekday-based rotation, specify ‘W0’ for Monday, ‘W1’ for Tuesday, and so on up to ‘W6’ for Sunday. In this case, the value passed for interval isn’t used. The system will save old log files by appending extensions to the filename. The extensions are date-and-time based, using the strftime format %Y-%m-%d_%H-%M-%S or a leading portion thereof, depending on the rollover interval. When computing the next rollover time for the first time (when the handler is created), the last modification time of an existing log file, or else the current time, is used to compute when the next rotation will occur. If the utc argument is true, times in UTC will be used; otherwise local time is used. If backupCount is nonzero, at most backupCount files will be kept, and if more would be created when rollover occurs, the oldest one is deleted. The deletion logic uses the interval to determine which files to delete, so changing the interval may leave old files lying around. If delay is true, then file opening is deferred until the first call to emit(). If atTime is not None, it must be a datetime.time instance which specifies the time of day when rollover occurs, for the cases where rollover is set to happen “at midnight” or “on a particular weekday”. Note that in these cases, the atTime value is effectively used to compute the initial rollover, and subsequent rollovers would be calculated via the normal interval calculation. If errors is specified, it’s used to determine how encoding errors are handled.  Note Calculation of the initial rollover time is done when the handler is initialised. Calculation of subsequent rollover times is done only when rollover occurs, and rollover occurs only when emitting output. If this is not kept in mind, it might lead to some confusion. For example, if an interval of “every minute” is set, that does not mean you will always see log files with times (in the filename) separated by a minute; if, during application execution, logging output is generated more frequently than once a minute, then you can expect to see log files with times separated by a minute. If, on the other hand, logging messages are only output once every five minutes (say), then there will be gaps in the file times corresponding to the minutes where no output (and hence no rollover) occurred.   Changed in version 3.4: atTime parameter was added.   Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
doRollover()
Does a rollover, as described above.

emit(record)
Outputs the record to the file, catering for rollover as described above.

 SocketHandler The SocketHandler class, located in the logging.handlers module, sends logging output to a network socket. The base class uses a TCP socket.
class logging.handlers.SocketHandler(host, port)
Returns a new instance of the SocketHandler class intended to communicate with a remote machine whose address is given by host and port.  Changed in version 3.4: If port is specified as None, a Unix domain socket is created using the value in host - otherwise, a TCP socket is created.
close()
Closes the socket.

emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. If the connection was previously lost, re-establishes the connection. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.

handleError()
Handles an error which has occurred during emit(). The most likely cause is a lost connection. Closes the socket so that we can retry on the next event.

makeSocket()
This is a factory method which allows subclasses to define the precise type of socket they want. The default implementation creates a TCP socket (socket.SOCK_STREAM).

makePickle(record)
Pickles the record’s attribute dictionary in binary format with a length prefix, and returns it ready for transmission across the socket. The details of this operation are equivalent to: data = pickle.dumps(record_attr_dict, 1)
datalen = struct.pack('>L', len(data))
return datalen + data
 Note that pickles aren’t completely secure. If you are concerned about security, you may want to override this method to implement a more secure mechanism. For example, you can sign pickles using HMAC and then verify them on the receiving end, or alternatively you can disable unpickling of global objects on the receiving end.

send(packet)
Send a pickled byte-string packet to the socket. The format of the sent byte-string is as described in the documentation for makePickle(). This function allows for partial sends, which can happen when the network is busy.

createSocket()
Tries to create a socket; on failure, uses an exponential back-off algorithm. On initial failure, the handler will drop the message it was trying to send. When subsequent messages are handled by the same instance, it will not try connecting until some time has passed. The default parameters are such that the initial delay is one second, and if after that delay the connection still can’t be made, the handler will double the delay each time up to a maximum of 30 seconds. This behaviour is controlled by the following handler attributes:
retryStart (initial delay, defaulting to 1.0 seconds).
retryFactor (multiplier, defaulting to 2.0).
retryMax (maximum delay, defaulting to 30.0 seconds).  This means that if the remote listener starts up after the handler has been used, you could lose messages (since the handler won’t even attempt a connection until the delay has elapsed, but just silently drop messages during the delay period).

 DatagramHandler The DatagramHandler class, located in the logging.handlers module, inherits from SocketHandler to support sending logging messages over UDP sockets.
class logging.handlers.DatagramHandler(host, port)
Returns a new instance of the DatagramHandler class intended to communicate with a remote machine whose address is given by host and port.  Changed in version 3.4: If port is specified as None, a Unix domain socket is created using the value in host - otherwise, a UDP socket is created.
emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.

makeSocket()
The factory method of SocketHandler is here overridden to create a UDP socket (socket.SOCK_DGRAM).

send(s)
Send a pickled byte-string to a socket. The format of the sent byte-string is as described in the documentation for SocketHandler.makePickle().

 SysLogHandler The SysLogHandler class, located in the logging.handlers module, supports sending logging messages to a remote or local Unix syslog.
class logging.handlers.SysLogHandler(address=('localhost', SYSLOG_UDP_PORT), facility=LOG_USER, socktype=socket.SOCK_DGRAM)
Returns a new instance of the SysLogHandler class intended to communicate with a remote Unix machine whose address is given by address in the form of a (host, port) tuple. If address is not specified, ('localhost', 514) is used. The address is used to open a socket. An alternative to providing a (host, port) tuple is providing an address as a string, for example ‘/dev/log’. In this case, a Unix domain socket is used to send the message to the syslog. If facility is not specified, LOG_USER is used. The type of socket opened depends on the socktype argument, which defaults to socket.SOCK_DGRAM and thus opens a UDP socket. To open a TCP socket (for use with the newer syslog daemons such as rsyslog), specify a value of socket.SOCK_STREAM. Note that if your server is not listening on UDP port 514, SysLogHandler may appear not to work. In that case, check what address you should be using for a domain socket - it’s system dependent. For example, on Linux it’s usually ‘/dev/log’ but on OS/X it’s ‘/var/run/syslog’. You’ll need to check your platform and use the appropriate address (you may need to do this check at runtime if your application needs to run on several platforms). On Windows, you pretty much have to use the UDP option.  Changed in version 3.2: socktype was added.
close()
Closes the socket to the remote host.

emit(record)
The record is formatted, and then sent to the syslog server. If exception information is present, it is not sent to the server.  Changed in version 3.2.1: (See: bpo-12168.) In earlier versions, the message sent to the syslog daemons was always terminated with a NUL byte, because early versions of these daemons expected a NUL terminated message - even though it’s not in the relevant specification (RFC 5424). More recent versions of these daemons don’t expect the NUL byte but strip it off if it’s there, and even more recent daemons (which adhere more closely to RFC 5424) pass the NUL byte on as part of the message. To enable easier handling of syslog messages in the face of all these differing daemon behaviours, the appending of the NUL byte has been made configurable, through the use of a class-level attribute, append_nul. This defaults to True (preserving the existing behaviour) but can be set to False on a SysLogHandler instance in order for that instance to not append the NUL terminator.   Changed in version 3.3: (See: bpo-12419.) In earlier versions, there was no facility for an “ident” or “tag” prefix to identify the source of the message. This can now be specified using a class-level attribute, defaulting to "" to preserve existing behaviour, but which can be overridden on a SysLogHandler instance in order for that instance to prepend the ident to every message handled. Note that the provided ident must be text, not bytes, and is prepended to the message exactly as is.

encodePriority(facility, priority)
Encodes the facility and priority into an integer. You can pass in strings or integers - if strings are passed, internal mapping dictionaries are used to convert them to integers. The symbolic LOG_ values are defined in SysLogHandler and mirror the values defined in the sys/syslog.h header file. Priorities
Name (string) Symbolic value
alert LOG_ALERT
crit or critical LOG_CRIT
debug LOG_DEBUG
emerg or panic LOG_EMERG
err or error LOG_ERR
info LOG_INFO
notice LOG_NOTICE
warn or warning LOG_WARNING   Facilities
Name (string) Symbolic value
auth LOG_AUTH
authpriv LOG_AUTHPRIV
cron LOG_CRON
daemon LOG_DAEMON
ftp LOG_FTP
kern LOG_KERN
lpr LOG_LPR
mail LOG_MAIL
news LOG_NEWS
syslog LOG_SYSLOG
user LOG_USER
uucp LOG_UUCP
local0 LOG_LOCAL0
local1 LOG_LOCAL1
local2 LOG_LOCAL2
local3 LOG_LOCAL3
local4 LOG_LOCAL4
local5 LOG_LOCAL5
local6 LOG_LOCAL6
local7 LOG_LOCAL7

mapPriority(levelname)
Maps a logging level name to a syslog priority name. You may need to override this if you are using custom levels, or if the default algorithm is not suitable for your needs. The default algorithm maps DEBUG, INFO, WARNING, ERROR and CRITICAL to the equivalent syslog names, and all other level names to ‘warning’.

 NTEventLogHandler The NTEventLogHandler class, located in the logging.handlers module, supports sending logging messages to a local Windows NT, Windows 2000 or Windows XP event log. Before you can use it, you need Mark Hammond’s Win32 extensions for Python installed.
class logging.handlers.NTEventLogHandler(appname, dllname=None, logtype='Application')
Returns a new instance of the NTEventLogHandler class. The appname is used to define the application name as it appears in the event log. An appropriate registry entry is created using this name. The dllname should give the fully qualified pathname of a .dll or .exe which contains message definitions to hold in the log (if not specified, 'win32service.pyd' is used - this is installed with the Win32 extensions and contains some basic placeholder message definitions. Note that use of these placeholders will make your event logs big, as the entire message source is held in the log. If you want slimmer logs, you have to pass in the name of your own .dll or .exe which contains the message definitions you want to use in the event log). The logtype is one of 'Application', 'System' or 'Security', and defaults to 'Application'.
close()
At this point, you can remove the application name from the registry as a source of event log entries. However, if you do this, you will not be able to see the events as you intended in the Event Log Viewer - it needs to be able to access the registry to get the .dll name. The current version does not do this.

emit(record)
Determines the message ID, event category and event type, and then logs the message in the NT event log.

getEventCategory(record)
Returns the event category for the record. Override this if you want to specify your own categories. This version returns 0.

getEventType(record)
Returns the event type for the record. Override this if you want to specify your own types. This version does a mapping using the handler’s typemap attribute, which is set up in __init__() to a dictionary which contains mappings for DEBUG, INFO, WARNING, ERROR and CRITICAL. If you are using your own levels, you will either need to override this method or place a suitable dictionary in the handler’s typemap attribute.

getMessageID(record)
Returns the message ID for the record. If you are using your own messages, you could do this by having the msg passed to the logger being an ID rather than a format string. Then, in here, you could use a dictionary lookup to get the message ID. This version returns 1, which is the base message ID in win32service.pyd.

 SMTPHandler The SMTPHandler class, located in the logging.handlers module, supports sending logging messages to an email address via SMTP.
class logging.handlers.SMTPHandler(mailhost, fromaddr, toaddrs, subject, credentials=None, secure=None, timeout=1.0)
Returns a new instance of the SMTPHandler class. The instance is initialized with the from and to addresses and subject line of the email. The toaddrs should be a list of strings. To specify a non-standard SMTP port, use the (host, port) tuple format for the mailhost argument. If you use a string, the standard SMTP port is used. If your SMTP server requires authentication, you can specify a (username, password) tuple for the credentials argument. To specify the use of a secure protocol (TLS), pass in a tuple to the secure argument. This will only be used when authentication credentials are supplied. The tuple should be either an empty tuple, or a single-value tuple with the name of a keyfile, or a 2-value tuple with the names of the keyfile and certificate file. (This tuple is passed to the smtplib.SMTP.starttls() method.) A timeout can be specified for communication with the SMTP server using the timeout argument.  New in version 3.3: The timeout argument was added.
emit(record)
Formats the record and sends it to the specified addressees.

getSubject(record)
If you want to specify a subject line which is record-dependent, override this method.

 MemoryHandler The MemoryHandler class, located in the logging.handlers module, supports buffering of logging records in memory, periodically flushing them to a target handler. Flushing occurs whenever the buffer is full, or when an event of a certain severity or greater is seen. MemoryHandler is a subclass of the more general BufferingHandler, which is an abstract class. This buffers logging records in memory. Whenever each record is added to the buffer, a check is made by calling shouldFlush() to see if the buffer should be flushed. If it should, then flush() is expected to do the flushing.
class logging.handlers.BufferingHandler(capacity)
Initializes the handler with a buffer of the specified capacity. Here, capacity means the number of logging records buffered.
emit(record)
Append the record to the buffer. If shouldFlush() returns true, call flush() to process the buffer.

flush()
You can override this to implement custom flushing behavior. This version just zaps the buffer to empty.

shouldFlush(record)
Return True if the buffer is up to capacity. This method can be overridden to implement custom flushing strategies.

class logging.handlers.MemoryHandler(capacity, flushLevel=ERROR, target=None, flushOnClose=True)
Returns a new instance of the MemoryHandler class. The instance is initialized with a buffer size of capacity (number of records buffered). If flushLevel is not specified, ERROR is used. If no target is specified, the target will need to be set using setTarget() before this handler does anything useful. If flushOnClose is specified as False, then the buffer is not flushed when the handler is closed. If not specified or specified as True, the previous behaviour of flushing the buffer will occur when the handler is closed.  Changed in version 3.6: The flushOnClose parameter was added.
close()
Calls flush(), sets the target to None and clears the buffer.

flush()
For a MemoryHandler, flushing means just sending the buffered records to the target, if there is one. The buffer is also cleared when this happens. Override if you want different behavior.

setTarget(target)
Sets the target handler for this handler.

shouldFlush(record)
Checks for buffer full or a record at the flushLevel or higher.

 HTTPHandler The HTTPHandler class, located in the logging.handlers module, supports sending logging messages to a Web server, using either GET or POST semantics.
class logging.handlers.HTTPHandler(host, url, method='GET', secure=False, credentials=None, context=None)
Returns a new instance of the HTTPHandler class. The host can be of the form host:port, should you need to use a specific port number. If no method is specified, GET is used. If secure is true, a HTTPS connection will be used. The context parameter may be set to a ssl.SSLContext instance to configure the SSL settings used for the HTTPS connection. If credentials is specified, it should be a 2-tuple consisting of userid and password, which will be placed in a HTTP ‘Authorization’ header using Basic authentication. If you specify credentials, you should also specify secure=True so that your userid and password are not passed in cleartext across the wire.  Changed in version 3.5: The context parameter was added.
mapLogRecord(record)
Provides a dictionary, based on record, which is to be URL-encoded and sent to the web server. The default implementation just returns record.__dict__. This method can be overridden if e.g. only a subset of LogRecord is to be sent to the web server, or if more specific customization of what’s sent to the server is required.

emit(record)
Sends the record to the Web server as a URL-encoded dictionary. The mapLogRecord() method is used to convert the record to the dictionary to be sent.
  Note Since preparing a record for sending it to a Web server is not the same as a generic formatting operation, using setFormatter() to specify a Formatter for a HTTPHandler has no effect. Instead of calling format(), this handler calls mapLogRecord() and then urllib.parse.urlencode() to encode the dictionary in a form suitable for sending to a Web server.
 QueueHandler  New in version 3.2.  The QueueHandler class, located in the logging.handlers module, supports sending logging messages to a queue, such as those implemented in the queue or multiprocessing modules. Along with the QueueListener class, QueueHandler can be used to let handlers do their work on a separate thread from the one which does the logging. This is important in Web applications and also other service applications where threads servicing clients need to respond as quickly as possible, while any potentially slow operations (such as sending an email via SMTPHandler) are done on a separate thread.
class logging.handlers.QueueHandler(queue)
Returns a new instance of the QueueHandler class. The instance is initialized with the queue to send messages to. The queue can be any queue-like object; it’s used as-is by the enqueue() method, which needs to know how to send messages to it. The queue is not required to have the task tracking API, which means that you can use SimpleQueue instances for queue.
emit(record)
Enqueues the result of preparing the LogRecord. Should an exception occur (e.g. because a bounded queue has filled up), the handleError() method is called to handle the error. This can result in the record silently being dropped (if logging.raiseExceptions is False) or a message printed to sys.stderr (if logging.raiseExceptions is True).

prepare(record)
Prepares a record for queuing. The object returned by this method is enqueued. The base implementation formats the record to merge the message, arguments, and exception information, if present. It also removes unpickleable items from the record in-place. You might want to override this method if you want to convert the record to a dict or JSON string, or send a modified copy of the record while leaving the original intact.

enqueue(record)
Enqueues the record on the queue using put_nowait(); you may want to override this if you want to use blocking behaviour, or a timeout, or a customized queue implementation.

 QueueListener  New in version 3.2.  The QueueListener class, located in the logging.handlers module, supports receiving logging messages from a queue, such as those implemented in the queue or multiprocessing modules. The messages are received from a queue in an internal thread and passed, on the same thread, to one or more handlers for processing. While QueueListener is not itself a handler, it is documented here because it works hand-in-hand with QueueHandler. Along with the QueueHandler class, QueueListener can be used to let handlers do their work on a separate thread from the one which does the logging. This is important in Web applications and also other service applications where threads servicing clients need to respond as quickly as possible, while any potentially slow operations (such as sending an email via SMTPHandler) are done on a separate thread.
class logging.handlers.QueueListener(queue, *handlers, respect_handler_level=False)
Returns a new instance of the QueueListener class. The instance is initialized with the queue to send messages to and a list of handlers which will handle entries placed on the queue. The queue can be any queue-like object; it’s passed as-is to the dequeue() method, which needs to know how to get messages from it. The queue is not required to have the task tracking API (though it’s used if available), which means that you can use SimpleQueue instances for queue. If respect_handler_level is True, a handler’s level is respected (compared with the level for the message) when deciding whether to pass messages to that handler; otherwise, the behaviour is as in previous Python versions - to always pass each message to each handler.  Changed in version 3.5: The respect_handler_level argument was added.
dequeue(block)
Dequeues a record and return it, optionally blocking. The base implementation uses get(). You may want to override this method if you want to use timeouts or work with custom queue implementations.

prepare(record)
Prepare a record for handling. This implementation just returns the passed-in record. You may want to override this method if you need to do any custom marshalling or manipulation of the record before passing it to the handlers.

handle(record)
Handle a record. This just loops through the handlers offering them the record to handle. The actual object passed to the handlers is that which is returned from prepare().

start()
Starts the listener. This starts up a background thread to monitor the queue for LogRecords to process.

stop()
Stops the listener. This asks the thread to terminate, and then waits for it to do so. Note that if you don’t call this before your application exits, there may be some records still left on the queue, which won’t be processed.

enqueue_sentinel()
Writes a sentinel to the queue to tell the listener to quit. This implementation uses put_nowait(). You may want to override this method if you want to use timeouts or work with custom queue implementations.  New in version 3.3.

  See also
Module logging

API reference for the logging module.
Module logging.config

Configuration API for the logging module.


class logging.handlers.BaseRotatingHandler(filename, mode, encoding=None, delay=False, errors=None)
The parameters are as for FileHandler. The attributes are:
namer
If this attribute is set to a callable, the rotation_filename() method delegates to this callable. The parameters passed to the callable are those passed to rotation_filename().  Note The namer function is called quite a few times during rollover, so it should be as simple and as fast as possible. It should also return the same output every time for a given input, otherwise the rollover behaviour may not work as expected.   New in version 3.3.

rotator
If this attribute is set to a callable, the rotate() method delegates to this callable. The parameters passed to the callable are those passed to rotate().  New in version 3.3.

rotation_filename(default_name)
Modify the filename of a log file when rotating. This is provided so that a custom filename can be provided. The default implementation calls the ‘namer’ attribute of the handler, if it’s callable, passing the default name to it. If the attribute isn’t callable (the default is None), the name is returned unchanged.  Parameters
default_name – The default name for the log file.    New in version 3.3.

rotate(source, dest)
When rotating, rotate the current log. The default implementation calls the ‘rotator’ attribute of the handler, if it’s callable, passing the source and dest arguments to it. If the attribute isn’t callable (the default is None), the source is simply renamed to the destination.  Parameters

source – The source filename. This is normally the base filename, e.g. ‘test.log’.
dest – The destination filename. This is normally what the source is rotated to, e.g. ‘test.log.1’.     New in version 3.3.


namer
If this attribute is set to a callable, the rotation_filename() method delegates to this callable. The parameters passed to the callable are those passed to rotation_filename().  Note The namer function is called quite a few times during rollover, so it should be as simple and as fast as possible. It should also return the same output every time for a given input, otherwise the rollover behaviour may not work as expected.   New in version 3.3.


rotate(source, dest)
When rotating, rotate the current log. The default implementation calls the ‘rotator’ attribute of the handler, if it’s callable, passing the source and dest arguments to it. If the attribute isn’t callable (the default is None), the source is simply renamed to the destination.  Parameters

source – The source filename. This is normally the base filename, e.g. ‘test.log’.
dest – The destination filename. This is normally what the source is rotated to, e.g. ‘test.log.1’.     New in version 3.3.


rotation_filename(default_name)
Modify the filename of a log file when rotating. This is provided so that a custom filename can be provided. The default implementation calls the ‘namer’ attribute of the handler, if it’s callable, passing the default name to it. If the attribute isn’t callable (the default is None), the name is returned unchanged.  Parameters
default_name – The default name for the log file.    New in version 3.3.


rotator
If this attribute is set to a callable, the rotate() method delegates to this callable. The parameters passed to the callable are those passed to rotate().  New in version 3.3.


class logging.handlers.BufferingHandler(capacity)
Initializes the handler with a buffer of the specified capacity. Here, capacity means the number of logging records buffered.
emit(record)
Append the record to the buffer. If shouldFlush() returns true, call flush() to process the buffer.

flush()
You can override this to implement custom flushing behavior. This version just zaps the buffer to empty.

shouldFlush(record)
Return True if the buffer is up to capacity. This method can be overridden to implement custom flushing strategies.


emit(record)
Append the record to the buffer. If shouldFlush() returns true, call flush() to process the buffer.


flush()
You can override this to implement custom flushing behavior. This version just zaps the buffer to empty.


shouldFlush(record)
Return True if the buffer is up to capacity. This method can be overridden to implement custom flushing strategies.


class logging.handlers.DatagramHandler(host, port)
Returns a new instance of the DatagramHandler class intended to communicate with a remote machine whose address is given by host and port.  Changed in version 3.4: If port is specified as None, a Unix domain socket is created using the value in host - otherwise, a UDP socket is created.
emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.

makeSocket()
The factory method of SocketHandler is here overridden to create a UDP socket (socket.SOCK_DGRAM).

send(s)
Send a pickled byte-string to a socket. The format of the sent byte-string is as described in the documentation for SocketHandler.makePickle().


emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.


makeSocket()
The factory method of SocketHandler is here overridden to create a UDP socket (socket.SOCK_DGRAM).


send(s)
Send a pickled byte-string to a socket. The format of the sent byte-string is as described in the documentation for SocketHandler.makePickle().


class logging.handlers.HTTPHandler(host, url, method='GET', secure=False, credentials=None, context=None)
Returns a new instance of the HTTPHandler class. The host can be of the form host:port, should you need to use a specific port number. If no method is specified, GET is used. If secure is true, a HTTPS connection will be used. The context parameter may be set to a ssl.SSLContext instance to configure the SSL settings used for the HTTPS connection. If credentials is specified, it should be a 2-tuple consisting of userid and password, which will be placed in a HTTP ‘Authorization’ header using Basic authentication. If you specify credentials, you should also specify secure=True so that your userid and password are not passed in cleartext across the wire.  Changed in version 3.5: The context parameter was added.
mapLogRecord(record)
Provides a dictionary, based on record, which is to be URL-encoded and sent to the web server. The default implementation just returns record.__dict__. This method can be overridden if e.g. only a subset of LogRecord is to be sent to the web server, or if more specific customization of what’s sent to the server is required.

emit(record)
Sends the record to the Web server as a URL-encoded dictionary. The mapLogRecord() method is used to convert the record to the dictionary to be sent.
  Note Since preparing a record for sending it to a Web server is not the same as a generic formatting operation, using setFormatter() to specify a Formatter for a HTTPHandler has no effect. Instead of calling format(), this handler calls mapLogRecord() and then urllib.parse.urlencode() to encode the dictionary in a form suitable for sending to a Web server.


emit(record)
Sends the record to the Web server as a URL-encoded dictionary. The mapLogRecord() method is used to convert the record to the dictionary to be sent.


mapLogRecord(record)
Provides a dictionary, based on record, which is to be URL-encoded and sent to the web server. The default implementation just returns record.__dict__. This method can be overridden if e.g. only a subset of LogRecord is to be sent to the web server, or if more specific customization of what’s sent to the server is required.


class logging.handlers.MemoryHandler(capacity, flushLevel=ERROR, target=None, flushOnClose=True)
Returns a new instance of the MemoryHandler class. The instance is initialized with a buffer size of capacity (number of records buffered). If flushLevel is not specified, ERROR is used. If no target is specified, the target will need to be set using setTarget() before this handler does anything useful. If flushOnClose is specified as False, then the buffer is not flushed when the handler is closed. If not specified or specified as True, the previous behaviour of flushing the buffer will occur when the handler is closed.  Changed in version 3.6: The flushOnClose parameter was added.
close()
Calls flush(), sets the target to None and clears the buffer.

flush()
For a MemoryHandler, flushing means just sending the buffered records to the target, if there is one. The buffer is also cleared when this happens. Override if you want different behavior.

setTarget(target)
Sets the target handler for this handler.

shouldFlush(record)
Checks for buffer full or a record at the flushLevel or higher.


close()
Calls flush(), sets the target to None and clears the buffer.


flush()
For a MemoryHandler, flushing means just sending the buffered records to the target, if there is one. The buffer is also cleared when this happens. Override if you want different behavior.


setTarget(target)
Sets the target handler for this handler.


shouldFlush(record)
Checks for buffer full or a record at the flushLevel or higher.


class logging.handlers.NTEventLogHandler(appname, dllname=None, logtype='Application')
Returns a new instance of the NTEventLogHandler class. The appname is used to define the application name as it appears in the event log. An appropriate registry entry is created using this name. The dllname should give the fully qualified pathname of a .dll or .exe which contains message definitions to hold in the log (if not specified, 'win32service.pyd' is used - this is installed with the Win32 extensions and contains some basic placeholder message definitions. Note that use of these placeholders will make your event logs big, as the entire message source is held in the log. If you want slimmer logs, you have to pass in the name of your own .dll or .exe which contains the message definitions you want to use in the event log). The logtype is one of 'Application', 'System' or 'Security', and defaults to 'Application'.
close()
At this point, you can remove the application name from the registry as a source of event log entries. However, if you do this, you will not be able to see the events as you intended in the Event Log Viewer - it needs to be able to access the registry to get the .dll name. The current version does not do this.

emit(record)
Determines the message ID, event category and event type, and then logs the message in the NT event log.

getEventCategory(record)
Returns the event category for the record. Override this if you want to specify your own categories. This version returns 0.

getEventType(record)
Returns the event type for the record. Override this if you want to specify your own types. This version does a mapping using the handler’s typemap attribute, which is set up in __init__() to a dictionary which contains mappings for DEBUG, INFO, WARNING, ERROR and CRITICAL. If you are using your own levels, you will either need to override this method or place a suitable dictionary in the handler’s typemap attribute.

getMessageID(record)
Returns the message ID for the record. If you are using your own messages, you could do this by having the msg passed to the logger being an ID rather than a format string. Then, in here, you could use a dictionary lookup to get the message ID. This version returns 1, which is the base message ID in win32service.pyd.


close()
At this point, you can remove the application name from the registry as a source of event log entries. However, if you do this, you will not be able to see the events as you intended in the Event Log Viewer - it needs to be able to access the registry to get the .dll name. The current version does not do this.


emit(record)
Determines the message ID, event category and event type, and then logs the message in the NT event log.


getEventCategory(record)
Returns the event category for the record. Override this if you want to specify your own categories. This version returns 0.


getEventType(record)
Returns the event type for the record. Override this if you want to specify your own types. This version does a mapping using the handler’s typemap attribute, which is set up in __init__() to a dictionary which contains mappings for DEBUG, INFO, WARNING, ERROR and CRITICAL. If you are using your own levels, you will either need to override this method or place a suitable dictionary in the handler’s typemap attribute.


getMessageID(record)
Returns the message ID for the record. If you are using your own messages, you could do this by having the msg passed to the logger being an ID rather than a format string. Then, in here, you could use a dictionary lookup to get the message ID. This version returns 1, which is the base message ID in win32service.pyd.


class logging.handlers.QueueHandler(queue)
Returns a new instance of the QueueHandler class. The instance is initialized with the queue to send messages to. The queue can be any queue-like object; it’s used as-is by the enqueue() method, which needs to know how to send messages to it. The queue is not required to have the task tracking API, which means that you can use SimpleQueue instances for queue.
emit(record)
Enqueues the result of preparing the LogRecord. Should an exception occur (e.g. because a bounded queue has filled up), the handleError() method is called to handle the error. This can result in the record silently being dropped (if logging.raiseExceptions is False) or a message printed to sys.stderr (if logging.raiseExceptions is True).

prepare(record)
Prepares a record for queuing. The object returned by this method is enqueued. The base implementation formats the record to merge the message, arguments, and exception information, if present. It also removes unpickleable items from the record in-place. You might want to override this method if you want to convert the record to a dict or JSON string, or send a modified copy of the record while leaving the original intact.

enqueue(record)
Enqueues the record on the queue using put_nowait(); you may want to override this if you want to use blocking behaviour, or a timeout, or a customized queue implementation.


emit(record)
Enqueues the result of preparing the LogRecord. Should an exception occur (e.g. because a bounded queue has filled up), the handleError() method is called to handle the error. This can result in the record silently being dropped (if logging.raiseExceptions is False) or a message printed to sys.stderr (if logging.raiseExceptions is True).


enqueue(record)
Enqueues the record on the queue using put_nowait(); you may want to override this if you want to use blocking behaviour, or a timeout, or a customized queue implementation.


prepare(record)
Prepares a record for queuing. The object returned by this method is enqueued. The base implementation formats the record to merge the message, arguments, and exception information, if present. It also removes unpickleable items from the record in-place. You might want to override this method if you want to convert the record to a dict or JSON string, or send a modified copy of the record while leaving the original intact.


class logging.handlers.QueueListener(queue, *handlers, respect_handler_level=False)
Returns a new instance of the QueueListener class. The instance is initialized with the queue to send messages to and a list of handlers which will handle entries placed on the queue. The queue can be any queue-like object; it’s passed as-is to the dequeue() method, which needs to know how to get messages from it. The queue is not required to have the task tracking API (though it’s used if available), which means that you can use SimpleQueue instances for queue. If respect_handler_level is True, a handler’s level is respected (compared with the level for the message) when deciding whether to pass messages to that handler; otherwise, the behaviour is as in previous Python versions - to always pass each message to each handler.  Changed in version 3.5: The respect_handler_level argument was added.
dequeue(block)
Dequeues a record and return it, optionally blocking. The base implementation uses get(). You may want to override this method if you want to use timeouts or work with custom queue implementations.

prepare(record)
Prepare a record for handling. This implementation just returns the passed-in record. You may want to override this method if you need to do any custom marshalling or manipulation of the record before passing it to the handlers.

handle(record)
Handle a record. This just loops through the handlers offering them the record to handle. The actual object passed to the handlers is that which is returned from prepare().

start()
Starts the listener. This starts up a background thread to monitor the queue for LogRecords to process.

stop()
Stops the listener. This asks the thread to terminate, and then waits for it to do so. Note that if you don’t call this before your application exits, there may be some records still left on the queue, which won’t be processed.

enqueue_sentinel()
Writes a sentinel to the queue to tell the listener to quit. This implementation uses put_nowait(). You may want to override this method if you want to use timeouts or work with custom queue implementations.  New in version 3.3.


dequeue(block)
Dequeues a record and return it, optionally blocking. The base implementation uses get(). You may want to override this method if you want to use timeouts or work with custom queue implementations.


enqueue_sentinel()
Writes a sentinel to the queue to tell the listener to quit. This implementation uses put_nowait(). You may want to override this method if you want to use timeouts or work with custom queue implementations.  New in version 3.3.


handle(record)
Handle a record. This just loops through the handlers offering them the record to handle. The actual object passed to the handlers is that which is returned from prepare().


prepare(record)
Prepare a record for handling. This implementation just returns the passed-in record. You may want to override this method if you need to do any custom marshalling or manipulation of the record before passing it to the handlers.


start()
Starts the listener. This starts up a background thread to monitor the queue for LogRecords to process.


stop()
Stops the listener. This asks the thread to terminate, and then waits for it to do so. Note that if you don’t call this before your application exits, there may be some records still left on the queue, which won’t be processed.


class logging.handlers.RotatingFileHandler(filename, mode='a', maxBytes=0, backupCount=0, encoding=None, delay=False, errors=None)
Returns a new instance of the RotatingFileHandler class. The specified file is opened and used as the stream for logging. If mode is not specified, 'a' is used. If encoding is not None, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call to emit(). By default, the file grows indefinitely. If errors is provided, it determines how encoding errors are handled. You can use the maxBytes and backupCount values to allow the file to rollover at a predetermined size. When the size is about to be exceeded, the file is closed and a new file is silently opened for output. Rollover occurs whenever the current log file is nearly maxBytes in length; but if either of maxBytes or backupCount is zero, rollover never occurs, so you generally want to set backupCount to at least 1, and have a non-zero maxBytes. When backupCount is non-zero, the system will save old log files by appending the extensions ‘.1’, ‘.2’ etc., to the filename. For example, with a backupCount of 5 and a base file name of app.log, you would get app.log, app.log.1, app.log.2, up to app.log.5. The file being written to is always app.log. When this file is filled, it is closed and renamed to app.log.1, and if files app.log.1, app.log.2, etc. exist, then they are renamed to app.log.2, app.log.3 etc. respectively.  Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
doRollover()
Does a rollover, as described above.

emit(record)
Outputs the record to the file, catering for rollover as described previously.


doRollover()
Does a rollover, as described above.


emit(record)
Outputs the record to the file, catering for rollover as described previously.


class logging.handlers.SMTPHandler(mailhost, fromaddr, toaddrs, subject, credentials=None, secure=None, timeout=1.0)
Returns a new instance of the SMTPHandler class. The instance is initialized with the from and to addresses and subject line of the email. The toaddrs should be a list of strings. To specify a non-standard SMTP port, use the (host, port) tuple format for the mailhost argument. If you use a string, the standard SMTP port is used. If your SMTP server requires authentication, you can specify a (username, password) tuple for the credentials argument. To specify the use of a secure protocol (TLS), pass in a tuple to the secure argument. This will only be used when authentication credentials are supplied. The tuple should be either an empty tuple, or a single-value tuple with the name of a keyfile, or a 2-value tuple with the names of the keyfile and certificate file. (This tuple is passed to the smtplib.SMTP.starttls() method.) A timeout can be specified for communication with the SMTP server using the timeout argument.  New in version 3.3: The timeout argument was added.
emit(record)
Formats the record and sends it to the specified addressees.

getSubject(record)
If you want to specify a subject line which is record-dependent, override this method.


emit(record)
Formats the record and sends it to the specified addressees.


getSubject(record)
If you want to specify a subject line which is record-dependent, override this method.


class logging.handlers.SocketHandler(host, port)
Returns a new instance of the SocketHandler class intended to communicate with a remote machine whose address is given by host and port.  Changed in version 3.4: If port is specified as None, a Unix domain socket is created using the value in host - otherwise, a TCP socket is created.
close()
Closes the socket.

emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. If the connection was previously lost, re-establishes the connection. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.

handleError()
Handles an error which has occurred during emit(). The most likely cause is a lost connection. Closes the socket so that we can retry on the next event.

makeSocket()
This is a factory method which allows subclasses to define the precise type of socket they want. The default implementation creates a TCP socket (socket.SOCK_STREAM).

makePickle(record)
Pickles the record’s attribute dictionary in binary format with a length prefix, and returns it ready for transmission across the socket. The details of this operation are equivalent to: data = pickle.dumps(record_attr_dict, 1)
datalen = struct.pack('>L', len(data))
return datalen + data
 Note that pickles aren’t completely secure. If you are concerned about security, you may want to override this method to implement a more secure mechanism. For example, you can sign pickles using HMAC and then verify them on the receiving end, or alternatively you can disable unpickling of global objects on the receiving end.

send(packet)
Send a pickled byte-string packet to the socket. The format of the sent byte-string is as described in the documentation for makePickle(). This function allows for partial sends, which can happen when the network is busy.

createSocket()
Tries to create a socket; on failure, uses an exponential back-off algorithm. On initial failure, the handler will drop the message it was trying to send. When subsequent messages are handled by the same instance, it will not try connecting until some time has passed. The default parameters are such that the initial delay is one second, and if after that delay the connection still can’t be made, the handler will double the delay each time up to a maximum of 30 seconds. This behaviour is controlled by the following handler attributes:
retryStart (initial delay, defaulting to 1.0 seconds).
retryFactor (multiplier, defaulting to 2.0).
retryMax (maximum delay, defaulting to 30.0 seconds).  This means that if the remote listener starts up after the handler has been used, you could lose messages (since the handler won’t even attempt a connection until the delay has elapsed, but just silently drop messages during the delay period).


createSocket()
Tries to create a socket; on failure, uses an exponential back-off algorithm. On initial failure, the handler will drop the message it was trying to send. When subsequent messages are handled by the same instance, it will not try connecting until some time has passed. The default parameters are such that the initial delay is one second, and if after that delay the connection still can’t be made, the handler will double the delay each time up to a maximum of 30 seconds. This behaviour is controlled by the following handler attributes:
retryStart (initial delay, defaulting to 1.0 seconds).
retryFactor (multiplier, defaulting to 2.0).
retryMax (maximum delay, defaulting to 30.0 seconds).  This means that if the remote listener starts up after the handler has been used, you could lose messages (since the handler won’t even attempt a connection until the delay has elapsed, but just silently drop messages during the delay period).


emit()
Pickles the record’s attribute dictionary and writes it to the socket in binary format. If there is an error with the socket, silently drops the packet. If the connection was previously lost, re-establishes the connection. To unpickle the record at the receiving end into a LogRecord, use the makeLogRecord() function.


handleError()
Handles an error which has occurred during emit(). The most likely cause is a lost connection. Closes the socket so that we can retry on the next event.


makePickle(record)
Pickles the record’s attribute dictionary in binary format with a length prefix, and returns it ready for transmission across the socket. The details of this operation are equivalent to: data = pickle.dumps(record_attr_dict, 1)
datalen = struct.pack('>L', len(data))
return datalen + data
 Note that pickles aren’t completely secure. If you are concerned about security, you may want to override this method to implement a more secure mechanism. For example, you can sign pickles using HMAC and then verify them on the receiving end, or alternatively you can disable unpickling of global objects on the receiving end.


makeSocket()
This is a factory method which allows subclasses to define the precise type of socket they want. The default implementation creates a TCP socket (socket.SOCK_STREAM).


send(packet)
Send a pickled byte-string packet to the socket. The format of the sent byte-string is as described in the documentation for makePickle(). This function allows for partial sends, which can happen when the network is busy.


class logging.handlers.SysLogHandler(address=('localhost', SYSLOG_UDP_PORT), facility=LOG_USER, socktype=socket.SOCK_DGRAM)
Returns a new instance of the SysLogHandler class intended to communicate with a remote Unix machine whose address is given by address in the form of a (host, port) tuple. If address is not specified, ('localhost', 514) is used. The address is used to open a socket. An alternative to providing a (host, port) tuple is providing an address as a string, for example ‘/dev/log’. In this case, a Unix domain socket is used to send the message to the syslog. If facility is not specified, LOG_USER is used. The type of socket opened depends on the socktype argument, which defaults to socket.SOCK_DGRAM and thus opens a UDP socket. To open a TCP socket (for use with the newer syslog daemons such as rsyslog), specify a value of socket.SOCK_STREAM. Note that if your server is not listening on UDP port 514, SysLogHandler may appear not to work. In that case, check what address you should be using for a domain socket - it’s system dependent. For example, on Linux it’s usually ‘/dev/log’ but on OS/X it’s ‘/var/run/syslog’. You’ll need to check your platform and use the appropriate address (you may need to do this check at runtime if your application needs to run on several platforms). On Windows, you pretty much have to use the UDP option.  Changed in version 3.2: socktype was added.
close()
Closes the socket to the remote host.

emit(record)
The record is formatted, and then sent to the syslog server. If exception information is present, it is not sent to the server.  Changed in version 3.2.1: (See: bpo-12168.) In earlier versions, the message sent to the syslog daemons was always terminated with a NUL byte, because early versions of these daemons expected a NUL terminated message - even though it’s not in the relevant specification (RFC 5424). More recent versions of these daemons don’t expect the NUL byte but strip it off if it’s there, and even more recent daemons (which adhere more closely to RFC 5424) pass the NUL byte on as part of the message. To enable easier handling of syslog messages in the face of all these differing daemon behaviours, the appending of the NUL byte has been made configurable, through the use of a class-level attribute, append_nul. This defaults to True (preserving the existing behaviour) but can be set to False on a SysLogHandler instance in order for that instance to not append the NUL terminator.   Changed in version 3.3: (See: bpo-12419.) In earlier versions, there was no facility for an “ident” or “tag” prefix to identify the source of the message. This can now be specified using a class-level attribute, defaulting to "" to preserve existing behaviour, but which can be overridden on a SysLogHandler instance in order for that instance to prepend the ident to every message handled. Note that the provided ident must be text, not bytes, and is prepended to the message exactly as is.

encodePriority(facility, priority)
Encodes the facility and priority into an integer. You can pass in strings or integers - if strings are passed, internal mapping dictionaries are used to convert them to integers. The symbolic LOG_ values are defined in SysLogHandler and mirror the values defined in the sys/syslog.h header file. Priorities
Name (string) Symbolic value
alert LOG_ALERT
crit or critical LOG_CRIT
debug LOG_DEBUG
emerg or panic LOG_EMERG
err or error LOG_ERR
info LOG_INFO
notice LOG_NOTICE
warn or warning LOG_WARNING   Facilities
Name (string) Symbolic value
auth LOG_AUTH
authpriv LOG_AUTHPRIV
cron LOG_CRON
daemon LOG_DAEMON
ftp LOG_FTP
kern LOG_KERN
lpr LOG_LPR
mail LOG_MAIL
news LOG_NEWS
syslog LOG_SYSLOG
user LOG_USER
uucp LOG_UUCP
local0 LOG_LOCAL0
local1 LOG_LOCAL1
local2 LOG_LOCAL2
local3 LOG_LOCAL3
local4 LOG_LOCAL4
local5 LOG_LOCAL5
local6 LOG_LOCAL6
local7 LOG_LOCAL7

mapPriority(levelname)
Maps a logging level name to a syslog priority name. You may need to override this if you are using custom levels, or if the default algorithm is not suitable for your needs. The default algorithm maps DEBUG, INFO, WARNING, ERROR and CRITICAL to the equivalent syslog names, and all other level names to ‘warning’.


close()
Closes the socket to the remote host.


emit(record)
The record is formatted, and then sent to the syslog server. If exception information is present, it is not sent to the server.  Changed in version 3.2.1: (See: bpo-12168.) In earlier versions, the message sent to the syslog daemons was always terminated with a NUL byte, because early versions of these daemons expected a NUL terminated message - even though it’s not in the relevant specification (RFC 5424). More recent versions of these daemons don’t expect the NUL byte but strip it off if it’s there, and even more recent daemons (which adhere more closely to RFC 5424) pass the NUL byte on as part of the message. To enable easier handling of syslog messages in the face of all these differing daemon behaviours, the appending of the NUL byte has been made configurable, through the use of a class-level attribute, append_nul. This defaults to True (preserving the existing behaviour) but can be set to False on a SysLogHandler instance in order for that instance to not append the NUL terminator.   Changed in version 3.3: (See: bpo-12419.) In earlier versions, there was no facility for an “ident” or “tag” prefix to identify the source of the message. This can now be specified using a class-level attribute, defaulting to "" to preserve existing behaviour, but which can be overridden on a SysLogHandler instance in order for that instance to prepend the ident to every message handled. Note that the provided ident must be text, not bytes, and is prepended to the message exactly as is.


encodePriority(facility, priority)
Encodes the facility and priority into an integer. You can pass in strings or integers - if strings are passed, internal mapping dictionaries are used to convert them to integers. The symbolic LOG_ values are defined in SysLogHandler and mirror the values defined in the sys/syslog.h header file. Priorities
Name (string) Symbolic value
alert LOG_ALERT
crit or critical LOG_CRIT
debug LOG_DEBUG
emerg or panic LOG_EMERG
err or error LOG_ERR
info LOG_INFO
notice LOG_NOTICE
warn or warning LOG_WARNING   Facilities
Name (string) Symbolic value
auth LOG_AUTH
authpriv LOG_AUTHPRIV
cron LOG_CRON
daemon LOG_DAEMON
ftp LOG_FTP
kern LOG_KERN
lpr LOG_LPR
mail LOG_MAIL
news LOG_NEWS
syslog LOG_SYSLOG
user LOG_USER
uucp LOG_UUCP
local0 LOG_LOCAL0
local1 LOG_LOCAL1
local2 LOG_LOCAL2
local3 LOG_LOCAL3
local4 LOG_LOCAL4
local5 LOG_LOCAL5
local6 LOG_LOCAL6
local7 LOG_LOCAL7


mapPriority(levelname)
Maps a logging level name to a syslog priority name. You may need to override this if you are using custom levels, or if the default algorithm is not suitable for your needs. The default algorithm maps DEBUG, INFO, WARNING, ERROR and CRITICAL to the equivalent syslog names, and all other level names to ‘warning’.


class logging.handlers.TimedRotatingFileHandler(filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False, atTime=None, errors=None)
Returns a new instance of the TimedRotatingFileHandler class. The specified file is opened and used as the stream for logging. On rotating it also sets the filename suffix. Rotating happens based on the product of when and interval. You can use the when to specify the type of interval. The list of possible values is below. Note that they are not case sensitive.
Value Type of interval If/how atTime is used
'S' Seconds Ignored
'M' Minutes Ignored
'H' Hours Ignored
'D' Days Ignored
'W0'-'W6' Weekday (0=Monday) Used to compute initial rollover time
'midnight' Roll over at midnight, if atTime not specified, else at time atTime Used to compute initial rollover time   When using weekday-based rotation, specify ‘W0’ for Monday, ‘W1’ for Tuesday, and so on up to ‘W6’ for Sunday. In this case, the value passed for interval isn’t used. The system will save old log files by appending extensions to the filename. The extensions are date-and-time based, using the strftime format %Y-%m-%d_%H-%M-%S or a leading portion thereof, depending on the rollover interval. When computing the next rollover time for the first time (when the handler is created), the last modification time of an existing log file, or else the current time, is used to compute when the next rotation will occur. If the utc argument is true, times in UTC will be used; otherwise local time is used. If backupCount is nonzero, at most backupCount files will be kept, and if more would be created when rollover occurs, the oldest one is deleted. The deletion logic uses the interval to determine which files to delete, so changing the interval may leave old files lying around. If delay is true, then file opening is deferred until the first call to emit(). If atTime is not None, it must be a datetime.time instance which specifies the time of day when rollover occurs, for the cases where rollover is set to happen “at midnight” or “on a particular weekday”. Note that in these cases, the atTime value is effectively used to compute the initial rollover, and subsequent rollovers would be calculated via the normal interval calculation. If errors is specified, it’s used to determine how encoding errors are handled.  Note Calculation of the initial rollover time is done when the handler is initialised. Calculation of subsequent rollover times is done only when rollover occurs, and rollover occurs only when emitting output. If this is not kept in mind, it might lead to some confusion. For example, if an interval of “every minute” is set, that does not mean you will always see log files with times (in the filename) separated by a minute; if, during application execution, logging output is generated more frequently than once a minute, then you can expect to see log files with times separated by a minute. If, on the other hand, logging messages are only output once every five minutes (say), then there will be gaps in the file times corresponding to the minutes where no output (and hence no rollover) occurred.   Changed in version 3.4: atTime parameter was added.   Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
doRollover()
Does a rollover, as described above.

emit(record)
Outputs the record to the file, catering for rollover as described above.


doRollover()
Does a rollover, as described above.


emit(record)
Outputs the record to the file, catering for rollover as described above.


class logging.handlers.WatchedFileHandler(filename, mode='a', encoding=None, delay=False, errors=None)
Returns a new instance of the WatchedFileHandler class. The specified file is opened and used as the stream for logging. If mode is not specified, 'a' is used. If encoding is not None, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call to emit(). By default, the file grows indefinitely. If errors is provided, it determines how encoding errors are handled.  Changed in version 3.6: As well as string values, Path objects are also accepted for the filename argument.   Changed in version 3.9: The errors parameter was added.
reopenIfNeeded()
Checks to see if the file has changed. If it has, the existing stream is flushed and closed and the file opened again, typically as a precursor to outputting the record to the file.  New in version 3.6.

emit(record)
Outputs the record to the file, but first calls reopenIfNeeded() to reopen the file if it has changed.


emit(record)
Outputs the record to the file, but first calls reopenIfNeeded() to reopen the file if it has changed.


reopenIfNeeded()
Checks to see if the file has changed. If it has, the existing stream is flushed and closed and the file opened again, typically as a precursor to outputting the record to the file.  New in version 3.6.


logging.info(msg, *args, **kwargs)
Logs a message with level INFO on the root logger. The arguments are interpreted as for debug().


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.


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.