twisted.python.log¶Note
There is now a new logging system in Twisted (you can read about how to use it here and its API reference here) which is a replacement for twisted.python.log.
The old logging API, described here, remains for compatibility, and is now implemented as a client of the new logging system.
New code should adopt the new API.
Twisted provides a simple and flexible logging system in the twisted.python.log module. It has three commonly used functions:
Logs a new message. For example:
from twisted.python import log log.msg('Hello, world.')
Writes a failure to the log, including traceback information (if any). You can pass it a Failure or Exception instance, or nothing. If you pass something else, it will be converted to a string with
reprand logged.If you pass nothing, it will construct a Failure from the currently active exception, which makes it convenient to use in an
exceptclause:try: x = 1 / 0 except: log.err() # will log the ZeroDivisionError
Starts logging to a given file-like object. For example:
log.startLogging(open('/var/log/foo.log', 'w'))or:
log.startLogging(sys.stdout)or:
from twisted.python.logfile import DailyLogFile log.startLogging(DailyLogFile.fromFullPath("/var/log/foo.log"))By default,
startLoggingwill also redirect anything written tosys.stdoutandsys.stderrto the log. You can disable this by passingsetStdout=FalsetostartLogging.
Before startLogging is called, log messages will be
discarded and errors will be written to stderr.
If you are using twistd to run your daemon, it
will take care of calling startLogging for you, and will also
rotate log files. See twistd and tac
and the twistd man page for details of using
twistd.
The twisted.python.logfile module provides
some standard classes suitable for use with startLogging , such
as DailyLogFile ,
which will rotate the log to a new file once per day.
If your application uses the Python standard library logging module or you want to use its easy configuration but don’t want to lose twisted-produced messages, the observer PythonLoggingObserver should be useful to you.
You just start it like any other observer:
observer = log.PythonLoggingObserver()
observer.start()
Then configure the standard library logging module to behave as you want.
This method allows you to customize the log level received by the
standard library logging module using the logLevel keyword:
log.msg("This is important!", logLevel=logging.CRITICAL)
log.msg("Don't mind", logLevel=logging.DEBUG)
Unless logLevel is provided, logging.INFO is used for log.msg
and logging.ERROR is used for log.err .
One special care should be made when you use special configuration of
the standard library logging module: some handlers (e.g. SMTP, HTTP) use the network and
so can block inside the reactor loop. Nothing in PythonLoggingObserver is
done to prevent that.
Log observers are the basis of the Twisted logging system.
Whenever log.msg (or log.err ) is called, an
event is emitted. The event is passed to each observer which has been
registered. There can be any number of observers, and each can treat
the event in any way desired.
An example of
a log observer in Twisted is the emit method of FileLogObserver .
FileLogObserver , used by
startLogging , writes events to a log file. A log observer
is just a callable that accepts a dictionary as its only argument. You can
then register it to receive all log events (in addition to any other
observers):
twisted.python.log.addObserver(yourCallable)
The dictionary will have at least two items:
message
The message (a list, usually of strings) for this log event, as passed tolog.msgor the message in the failure passed tolog.err.
isError
This is a boolean that will be true if this event came from a call tolog.err. If this is set, there may be afailureitem in the dictionary as will, with a Failure object in it.
Other items the built in logging functionality may add include:
printed
This message was captured fromsys.stdout, i.e. this message came from aisErroris also true, it came fromsys.stderr.
You can pass additional items to the event dictionary by passing keyword
arguments to log.msg and log.err . The standard
log observers will ignore dictionary items they don’t use.
Important notes:
twistd logging¶The behavior of the logging that twistd does can be
customized either with the --logger option or by setting the
ILogObserver component on the application object. See the Application document for more information.