From cce638a8adf4e045ca5505afea4bda57753c31dd Mon Sep 17 00:00:00 2001 From: Micah Anderson Date: Mon, 11 Aug 2014 16:33:29 -0400 Subject: initial import of debian package --- docs/source/logging.rst | 84 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 84 insertions(+) create mode 100644 docs/source/logging.rst (limited to 'docs/source/logging.rst') diff --git a/docs/source/logging.rst b/docs/source/logging.rst new file mode 100644 index 0000000..ea16da3 --- /dev/null +++ b/docs/source/logging.rst @@ -0,0 +1,84 @@ +.. PyZMQ logging doc, by Min Ragan-Kelley, 2011 + +.. _logging: + +Asynchronous Logging via PyZMQ +============================== + +.. seealso:: + + * The ØMQ guide `coverage `_ of PUB/SUB + messaging + * Python logging module `documentation `_ + +Python provides extensible logging facilities through its :py:mod:`logging` module. This +module allows for easily extensible logging functionality through the use of +:py:class:`~logging.Handler` objects. The most obvious case for hooking up pyzmq to +logging would be to broadcast log messages over a PUB socket, so we have provides a +:class:`.PUBHandler` class for doing just that. + +PUB/SUB and Topics +------------------ + +The ØMQ PUB/SUB pattern consists of a PUB socket broadcasting messages, and a collection +of SUB sockets that receive those messages. Each PUB message is a multipart-message, where +the first part is interpreted as a topic. SUB sockets can subscribe to topics by setting +their ``SUBSCRIBE`` sockopt, e.g.:: + + sub = ctx.socket(zmq.SUB) + sub.setsockopt(zmq.SUBSCRIBE, 'topic1') + sub.setsockopt(zmq.SUBSCRIBE, 'topic2') + +When subscribed, the SUB socket will only receive messages where the first part *starts +with* one of the topics set via ``SUBSCRIBE``. The default behavior is to exclude all +messages, and subscribing to the empty string '' will receive all messages. + +PUBHandler +---------- + +The :class:`.PUBHandler` object is created for allowing the python logging to be emitted +on a PUB socket. The main difference between a PUBHandler and a regular logging Handler is +the inclusion of topics. For the most basic logging, you can simply create a PUBHandler +with an interface or a configured PUB socket, and just let it go:: + + pub = context.socket(zmq.PUB) + pub.bind('tcp://*:12345') + handler = PUBHandler(pub) + logger = logging.getLogger() + logger.addHandler(handler) + +At this point, all messages logged with the default logger will be broadcast on the pub +socket. + +the PUBHandler does work with topics, and the handler has an attribute ``root_topic``:: + + handler.root_topic = 'myprogram' + +Python loggers also have loglevels. The base topic of messages emitted by the PUBHandler +will be of the form: ``.``, e.g. 'myprogram.INFO' or +'whatever.ERROR'. This way, subscribers can easily subscribe to subsets of the logging +messages. Log messages are always two-part, where the first part is the topic tree, and +the second part is the actual log message. + + >>> logger.info('hello there') + >>> print sub.recv_multipart() + ['myprogram.INFO', 'hello there'] + +Subtopics +********* + +You can also add to the topic tree below the loglevel on an individual message basis. +Assuming your logger is connected to a PUBHandler, you can add as many additional topics +on the front of the message, which will be added always after the loglevel. A special +delimiter defined at ``zmq.log.handlers.TOPIC_DELIM`` is scanned by the PUBHandler, so if +you pass your own subtopics prior to that symbol, they will be stripped from the message +and added to the topic tree:: + + >>> log_msg = "hello there" + >>> subtopic = "sub.topic" + >>> msg = zmq.log.handlers.TOPIC_DELIM.join([subtopic, log_msg]) + >>> logger.warn(msg) + >>> print sub.recv_multipart() + ['myprogram.WARN.sub.topic', 'hello there'] + + -- cgit v1.2.3