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.

NOTICE: Python2.7 is only supported up to v0.1.11. The next release, v2.0, will support Python3 only.

Installing

Pip:

pip install python-json-logger

Pypi:

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

Manual:

python setup.py install

Usage

Integrating with Python's logging framework

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

Please note: version 0.1.0 has changed the import structure, please update to the following example for proper importing

    import logging
    from pythonjsonlogger import jsonlogger

    logger = logging.getLogger()

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

Customizing fields

The fmt parser can also be overidden if you want to have required fields that differ from the default of just message.

These two invocations are equivalent:

class CustomJsonFormatter(jsonlogger.JsonFormatter):
    def parse(self):
        return self._fmt.split(';')

formatter = CustomJsonFormatter('one;two')

# is equivalent to:

formatter = jsonlogger.JsonFormatter('(one) (two)')

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.

You can also use the add_fields method to add to or generally normalize the set of default set of fields, it is called for every log event. For example, to unify default fields with those provided by structlog you could do something like this:

class CustomJsonFormatter(jsonlogger.JsonFormatter):
    def add_fields(self, log_record, record, message_dict):
        super(CustomJsonFormatter, self).add_fields(log_record, record, message_dict)
        if not log_record.get('timestamp'):
            # this doesn't use record.created, so it is slightly off
            now = datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%S.%fZ')
            log_record['timestamp'] = now
        if log_record.get('level'):
            log_record['level'] = log_record['level'].upper()
        else:
            log_record['level'] = record.levelname

formatter = CustomJsonFormatter('(timestamp) (level) (name) (message)')

Items added to the log record will be included in every log message, no matter what the format requires.

Adding custom object serialization

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})

Using a Config File

To use the module with a config file using the fileConfig function, use the class pythonjsonlogger.jsonlogger.JsonFormatter. Here is a sample config file.

[loggers]
keys = root,custom

[logger_root]
handlers =

[logger_custom]
level = INFO
handlers = custom
qualname = custom

[handlers]
keys = custom

[handler_custom]
class = StreamHandler
level = INFO
formatter = json
args = (sys.stdout,)

[formatters]
keys = json

[formatter_json]
format = %(message)s
class = pythonjsonlogger.jsonlogger.JsonFormatter

Example Output

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.

{
    "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
}

External Examples

• Wesley Tanaka - Structured log files in Python using python-json-logger