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authorVinay Sajip <vinay_sajip@yahoo.co.uk>2013-01-22 15:57:39 (GMT)
committerVinay Sajip <vinay_sajip@yahoo.co.uk>2013-01-22 15:57:39 (GMT)
commit4b88d6c6642450240a9dc22e6efbdc69baf890dd (patch)
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Added cookbook recipe for structured logging.
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diff --git a/Doc/howto/logging-cookbook.rst b/Doc/howto/logging-cookbook.rst
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@@ -1588,3 +1588,78 @@ The formatted message *will* be encoded using UTF-8 encoding by
RFC 5424-compliant messages. If you don't, logging may not complain, but your
messages will not be RFC 5424-compliant, and your syslog daemon may complain.
+
+Implementing structured logging
+-------------------------------
+
+Although most logging messages are intended for reading by humans, and thus not
+readily machine-parseable, there might be cirumstances where you want to output
+messages in a structured format which *is* capable of being parsed by a program
+(without needed complex regular expressions to parse the log message). This is
+straightforward to achieve using the logging package. There are a number of
+ways in which this could be achieved, but the following is a simple approach
+which uses JSON to serialise the event in a machine-parseable manner::
+
+ import json
+ import logging
+
+ class StructuredMessage(object):
+ def __init__(self, message, **kwargs):
+ self.message = message
+ self.kwargs = kwargs
+
+ def __str__(self):
+ return '%s >>> %s' % (self.message, json.dumps(self.kwargs))
+
+ _ = StructuredMessage # optional, to improve readability
+
+ logging.basicConfig(level=logging.INFO, format='%(message)s')
+ logging.info(_('message 1', foo='bar', bar='baz', num=123, fnum=123.456))
+
+If the above script is run, it prints::
+
+ message 1 >>> {"fnum": 123.456, "num": 123, "bar": "baz", "foo": "bar"}
+
+If you need more specialised processing, you can use a custom JSON encoder,
+as in the following complete example::
+
+ from __future__ import unicode_literals
+
+ import json
+ import logging
+
+ try:
+ unicode
+ except NameError:
+ unicode = str
+
+ class Encoder(json.JSONEncoder):
+ def default(self, o):
+ if isinstance(o, set):
+ return tuple(o)
+ elif isinstance(o, unicode):
+ return o.encode('unicode_escape').decode('ascii')
+ return super(Encoder, self).default(o)
+
+ class StructuredMessage(object):
+ def __init__(self, message, **kwargs):
+ self.message = message
+ self.kwargs = kwargs
+
+ def __str__(self):
+ s = Encoder().encode(self.kwargs)
+ return '%s >>> %s' % (self.message, s)
+
+ _ = StructuredMessage
+
+ def main():
+ logging.basicConfig(level=logging.INFO, format='%(message)s')
+ logging.info(_('message 1', set_value=set([1, 2, 3]), snowman='\u2603'))
+
+ if __name__ == '__main__':
+ main()
+
+When the above script is run, it prints::
+
+ message 1 >>> {"snowman": "\u2603", "set_value": [1, 2, 3]}
+