Overview

This library is provided to allow standard python logging to output log data as json objects. With JSON we can make our logs more readable by machines and we can stop writing custom parsers for syslog type records.

Installing

Pip:

pip install python-json-logger

Pypi:

https://pypi.python.org/pypi/python-json-logger

Manual:

python setup.py install

Usage

Json outputs are provided by the JsonFormatter logging formatter. You can add the customer formatter like below:

    import logging
    import jsonlogger

    logger = logging.getLogger()

    logHandler = logging.StreamHandler()
    formatter = jsonlogger.JsonFormatter()
    logHandler.setFormatter(formatter)
    logger.addHandler(logHandler)

The fmt parser can also be overiden if you want to use an alternate from the default.

    class CustomJsonFormatter(jsonlogger.JsonFormatter):
      def parse(self):
          return eval(self._fmt)

You can also add extra fields to your json output by specifying a dict in place of message, as well as by specifying an extra={} argument. Contents of these dictionaries will be added at the root level of the entry and may override basic fields. For custom handling of object serialization you can specify default json object translator or provide a custom encoder

    def json_translate(obj):
        if isinstance(obj, MyClass):
            return {"special": obj.special}

    formatter = jsonlogger.JsonFormatter(json_default=json_translate,
                                         json_encoder=json.JSONEncoder())
    logHandler.setFormatter(formatter)

    logger.info({"special": "value", "run": 12})
    logger.info("classic message", extra={"special": "value", "run": 12})

Example

Sample JSON with a full formatter (basically the log message from the unit test). Every log message will appear on 1 line like a typical logger. If logger.exception method is called or exc_info is set then an "excType", "excValue" and "excTrace" properties will be added to the output.

{
    "threadName": "MainThread",
    "name": "root",
    "thread": 140735202359648,
    "created": 1336281068.506248,
    "process": 41937,
    "processName": "MainProcess",
    "relativeCreated": 9.100914001464844,
    "module": "tests",
    "funcName": "testFormatKeys",
    "levelno": 20,
    "msecs": 506.24799728393555,
    "pathname": "tests/tests.py",
    "lineno": 60,
    "asctime": ["12-05-05 22:11:08,506248"],
    "message": "testing logging format",
    "filename": "tests.py",
    "levelname": "INFO",
    "special": "value",
    "run": 12,
    "excType": "exceptions.Exception",
    "excValue": "Some exception message",
    "excTrace": [
        {
            "lineno": 32,
            "name": "some_function_name",
            "filename": "/path/to/source/file.py"
        }
    ]
}