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| -rw-r--r-- | Doc/howto/logging-cookbook.rst | 87 |
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diff --git a/Doc/howto/logging-cookbook.rst b/Doc/howto/logging-cookbook.rst index 674695b..563da9d 100644 --- a/Doc/howto/logging-cookbook.rst +++ b/Doc/howto/logging-cookbook.rst @@ -1694,6 +1694,9 @@ When the above script is run, it prints:: Note that the order of items might be different according to the version of Python used. + +.. _custom-handlers: + .. currentmodule:: logging.config Customizing handlers with :func:`dictConfig` @@ -1948,3 +1951,87 @@ handler. So the only slightly unusual thing which might trip you up is that the parentheses go around the format string and the arguments, not just the format string. That’s because the __ notation is just syntax sugar for a constructor call to one of the ``XXXMessage`` classes shown above. + + +.. _filters-dictconfig: + +.. currentmodule:: logging.config + +Configuring filters with :func:`dictConfig` +------------------------------------------- + +You *can* configure filters using :func:`~logging.config.dictConfig`, though it +might not be obvious at first glance how to do it (hence this recipe). Since +:class:`~logging.Filter` is the only filter class included in the standard +library, and it is unlikely to cater to many requirements (it's only there as a +base class), you will typically need to define your own :class:`~logging.Filter` +subclass with an overridden :meth:`~logging.Filter.filter` method. To do this, +specify the ``()`` key in the configuration dictionary for the filter, +specifying a callable which will be used to create the filter (a class is the +most obvious, but you can provide any callable which returns a +:class:`~logging.Filter` instance). Here is a complete example:: + + import logging + import logging.config + import sys + + class MyFilter(logging.Filter): + def __init__(self, param=None): + self.param = param + + def filter(self, record): + if self.param is None: + allow = True + else: + allow = self.param not in record.msg + if allow: + record.msg = 'changed: ' + record.msg + return allow + + LOGGING = { + 'version': 1, + 'filters': { + 'myfilter': { + '()': MyFilter, + 'param': 'noshow', + } + }, + 'handlers': { + 'console': { + 'class': 'logging.StreamHandler', + 'filters': ['myfilter'] + } + }, + 'root': { + 'level': 'DEBUG', + 'handlers': ['console'] + }, + } + + if __name__ == '__main__': + logging.config.dictConfig(LOGGING) + logging.debug('hello') + logging.debug('hello - noshow') + +This example shows how you can pass configuration data to the callable which +constructs the instance, in the form of keyword parameters. When run, the above +script will print:: + + changed: hello + +which shows that the filter is working as configured. + +A couple of extra points to note: + +* If you can't refer to the callable directly in the configuration (e.g. if it + lives in a different module, and you can't import it directly where the + configuration dictionary is), you can use the form ``ext://...`` as described + in :ref:`logging-config-dict-externalobj`. For example, you could have used + the text ``'ext://__main__.MyFilter'`` instead of ``MyFilter`` in the above + example. + +* As well as for filters, this technique can also be used to configure custom + handlers and formatters. See :ref:`logging-config-dict-userdef` for more + information on how logging supports using user-defined objects in its + configuration, and see the other cookbook recipe :ref:`custom-handlers` above. + |