diff --git a/Doc/library/logging.rst b/Doc/library/logging.rst index e82be99f9bb..215b20db112 100644 --- a/Doc/library/logging.rst +++ b/Doc/library/logging.rst @@ -1335,6 +1335,10 @@ level of granularity you want to use in logging an application, it could be hard to manage if the number of :class:`Logger` instances becomes effectively unbounded. + +Using LoggerAdapters to impart contextual information +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + An easy way in which you can pass contextual information to be output along with logging event information is to use the :class:`LoggerAdapter` class. This class is designed to look like a :class:`Logger`, so that you can call @@ -1442,6 +1446,78 @@ When this script is run, the output should look something like this:: The :class:`LoggerAdapter` class was not present in previous versions. +Using Filters to impart contextual information +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +You can also add contextual information to log output using a user-defined +:class:`Filter`. ``Filter`` instances are allowed to modify the ``LogRecords`` +passed to them, including adding additional attributes which can then be output +using a suitable format string, or if needed a custom :class:`Formatter`. + +For example in a web application, the request being processed (or at least, +the interesting parts of it) can be stored in a threadlocal +(:class:`threading.local`) variable, and then accessed from a ``Filter`` to +add, say, information from the request - say, the remote IP address and remote +user's username - to the ``LogRecord``, using the attribute names 'ip' and +'user' as in the ``LoggerAdapter`` example above. In that case, the same format +string can be used to get similar output to that shown above. Here's an example +script:: + + import logging + from random import choice + + class ContextFilter(logging.Filter): + """ + This is a filter which injects contextual information into the log. + + Rather than use actual contextual information, we just use random + data in this demo. + """ + + USERS = ['jim', 'fred', 'sheila'] + IPS = ['123.231.231.123', '127.0.0.1', '192.168.0.1'] + + def filter(self, record): + + record.ip = choice(ContextFilter.IPS) + record.user = choice(ContextFilter.USERS) + return True + + if __name__ == "__main__": + levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL) + a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"), + { "ip" : "123.231.231.123", "user" : "sheila" }) + logging.basicConfig(level=logging.DEBUG, + format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s") + a1 = logging.getLogger("a.b.c") + a2 = logging.getLogger("d.e.f") + + f = ContextFilter() + a1.addFilter(f) + a2.addFilter(f) + a1.debug("A debug message") + a1.info("An info message with %s", "some parameters") + for x in range(10): + lvl = choice(levels) + lvlname = logging.getLevelName(lvl) + a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters") + +which, when run, produces something like:: + + 2010-09-06 22:38:15,292 a.b.c DEBUG IP: 123.231.231.123 User: fred A debug message + 2010-09-06 22:38:15,300 a.b.c INFO IP: 192.168.0.1 User: sheila An info message with some parameters + 2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1 User: sheila A message at CRITICAL level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f ERROR IP: 127.0.0.1 User: jim A message at ERROR level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f DEBUG IP: 127.0.0.1 User: sheila A message at DEBUG level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f ERROR IP: 123.231.231.123 User: fred A message at ERROR level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 192.168.0.1 User: jim A message at CRITICAL level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1 User: sheila A message at CRITICAL level with 2 parameters + 2010-09-06 22:38:15,300 d.e.f DEBUG IP: 192.168.0.1 User: jim A message at DEBUG level with 2 parameters + 2010-09-06 22:38:15,301 d.e.f ERROR IP: 127.0.0.1 User: sheila A message at ERROR level with 2 parameters + 2010-09-06 22:38:15,301 d.e.f DEBUG IP: 123.231.231.123 User: fred A message at DEBUG level with 2 parameters + 2010-09-06 22:38:15,301 d.e.f INFO IP: 123.231.231.123 User: fred A message at INFO level with 2 parameters + + .. _multiple-processes: Logging to a single file from multiple processes