16.8. logging.handlers
— Logging handlers¶
Source code: Lib/logging/handlers.py
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.
16.8.1. 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 with a terminator. If exception information is present, it is formatted using
traceback.print_exception()
and appended to the stream.
-
Distinto en la versión 3.2: The StreamHandler
class now has a terminator
attribute, default
value '\n'
, which is used as the terminator when writing a formatted
record to a stream. If you don’t want this newline termination, you can
set the handler instance’s terminator
attribute to the empty string.
In earlier versions, the terminator was hardcoded as '\n'
.
16.8.2. 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)¶ 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 notNone
, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call toemit()
. By default, the file grows indefinitely.-
close
()¶ Closes the file.
-
emit
(record)¶ Outputs the record to the file.
-
16.8.3. NullHandler¶
Nuevo en la versión 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
.
16.8.4. 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)¶ 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 notNone
, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call toemit()
. By default, the file grows indefinitely.-
emit
(record)¶ Outputs the record to the file, but first checks to see if the file has changed. If it has, the existing stream is flushed and closed and the file opened again, before outputting the record to the file.
-
16.8.5. 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)¶ 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 torotation_filename()
.Nota
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.
Nuevo en la versión 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 torotate()
.Nuevo en la versión 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.Parámetros: default_name – The default name for the log file. Nuevo en la versión 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.Parámetros: - 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”.
Nuevo en la versión 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.
16.8.6. 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)¶ 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 notNone
, it is used to open the file with that encoding. If delay is true, then file opening is deferred until the first call toemit()
. By default, the file grows indefinitely.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; if either of maxBytes or backupCount is zero, rollover never occurs. If 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 getapp.log
,app.log.1
,app.log.2
, up toapp.log.5
. The file being written to is alwaysapp.log
. When this file is filled, it is closed and renamed toapp.log.1
, and if filesapp.log.1
,app.log.2
, etc. exist, then they are renamed toapp.log.2
,app.log.3
etc. respectively.-
doRollover
()¶ Does a rollover, as described above.
-
emit
(record)¶ Outputs the record to the file, catering for rollover as described previously.
-
16.8.7. 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)¶ 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 'S'
Seconds 'M'
Minutes 'H'
Hours 'D'
Days 'W0'-'W6'
Weekday (0=Monday) 'midnight'
Roll over at midnight 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 adatetime.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».Distinto en la versión 3.4: atTime parameter was added.
-
doRollover
()¶ Does a rollover, as described above.
-
emit
(record)¶ Outputs the record to the file, catering for rollover as described above.
-
16.8.8. 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.Distinto en la versión 3.4: If
port
is specified asNone
, a Unix domain socket is created using the value inhost
- 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 themakeLogRecord()
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.
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 string packet to the socket. 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).
-
16.8.9. 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.Distinto en la versión 3.4: If
port
is specified asNone
, a Unix domain socket is created using the value inhost
- otherwise, a TCP 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 themakeLogRecord()
function.
-
makeSocket
()¶ The factory method of
SocketHandler
is here overridden to create a UDP socket (socket.SOCK_DGRAM
).
-
send
(s)¶ Send a pickled string to a socket.
-
16.8.10. 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 tosocket.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 ofsocket.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.Distinto en la versión 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.
Distinto en la versión 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 toTrue
(preserving the existing behaviour) but can be set toFalse
on aSysLogHandler
instance in order for that instance to not append the NUL terminator.Distinto en la versión 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 aSysLogHandler
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 inSysLogHandler
and mirror the values defined in thesys/syslog.h
header file.Priorities
Name (string) Symbolic value alert
LOG_ALERT crit
orcritical
LOG_CRIT debug
LOG_DEBUG emerg
orpanic
LOG_EMERG err
orerror
LOG_ERR info
LOG_INFO notice
LOG_NOTICE warn
orwarning
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
andCRITICAL
to the equivalent syslog names, and all other level names to “warning”.
-
16.8.11. 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 forDEBUG
,INFO
,WARNING
,ERROR
andCRITICAL
. 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
.
-
16.8.12. 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.
Nuevo en la versión 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.
-
16.8.13. 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.
-
emit
(record)¶ Appends the record to the buffer. If
shouldFlush()
returns true, callsflush()
to process the buffer.
-
flush
()¶ You can override this to implement custom flushing behavior. This version just zaps the buffer to empty.
-
shouldFlush
(record)¶ Returns 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)¶ Returns a new instance of the
MemoryHandler
class. The instance is initialized with a buffer size of capacity. If flushLevel is not specified,ERROR
is used. If no target is specified, the target will need to be set usingsetTarget()
before this handler does anything useful.-
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.
-
16.8.14. 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 formhost: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 assl.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.Distinto en la versión 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 returnsrecord.__dict__
. This method can be overridden if e.g. only a subset ofLogRecord
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.
Nota
Since preparing a record for sending it to a Web server is not the same as a generic formatting operation, using
setFormatter()
to specify aFormatter
for aHTTPHandler
has no effect. Instead of callingformat()
, this handler callsmapLogRecord()
and thenurllib.parse.urlencode()
to encode the dictionary in a form suitable for sending to a Web server.-
16.8.15. QueueHandler¶
Nuevo en la versión 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 theenqueue()
method, which needs to know how to send messages to it.-
emit
(record)¶ Enqueues the result of preparing the LogRecord.
-
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 and arguments, and 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.
-
16.8.16. QueueListener¶
Nuevo en la versión 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 thedequeue()
method, which needs to know how to get messages from it. Ifrespect_handler_level
isTrue
, 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.Distinto en la versión 3.5: The
respect_handler_levels
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.Nuevo en la versión 3.3.
-
Ver también
- Module
logging
- API reference for the logging module.
- Module
logging.config
- Configuration API for the logging module.