How to log to JSON

json_logging.py

#!/usr/bin/env python
import json
import logging


class JSONFormatter:
    """
    A simple formatter class which takes a record and return the fields
    in JSON format
    """
    def __init__(self, json_encoder=None):
        self.json_encoder = json_encoder or json.JSONEncoder()

    def format(self, record):
        return self.json_encoder.encode(record.__dict__)


class JSONHandler(logging.StreamHandler):
    """
    A JSON handler which writes each record as a dictionary
    """
    def __init__(self, stream=None):
        super(JSONHandler, self).__init__(stream)
        self.before_first_record = True

    def emit(self, record):
        """
        For each log record (AKA line), emit as JSON
        """
        self.acquire()

        if self.before_first_record:
            self.stream.write('[\n')
        else:
            self.stream.write(',\n')
        self.before_first_record = False

        self.stream.write(self.format(record))
        self.flush()

        self.release()

    def close(self):
        """
        Write the closing part of the JSON
        """
        self.acquire()
        self.stream.write('\n]\n')
        self.flush()
        self.release()


def get_logger(name, level=logging.WARN, json_encoder=None):
    """
    Convenient factory function to create a new logger which employs
    the JSONHandler
    """
    logger = logging.getLogger(__name__)
    logger.setLevel(level)

    handler = JSONHandler()
    formatter = JSONFormatter(json_encoder=json_encoder)
    handler.setFormatter(formatter)
    logger.addHandler(handler)
    return logger


def main():
    logger = get_logger(
        __name__,
        level=logging.DEBUG,
        json_encoder=json.JSONEncoder(indent=4, sort_keys=True))

    # Start logging
    logger.info('Preparing breakfast')
    logger.warn('Almost out of coffee')
    logger.error(
        'error: %s, line %d, file %s',
        'out of milk', 51, 'cow.java')
    logger.debug('This is debug')


if __name__ == '__main__':
    main()

output.json

[
{
    "args": [], 
    "created": 1504232368.014854, 
    "exc_info": null, 
    "exc_text": null, 
    "filename": "json_logging.py", 
    "funcName": "main", 
    "levelname": "INFO", 
    "levelno": 20, 
    "lineno": 51, 
    "module": "json_logging", 
    "msecs": 14.853954315185547, 
    "msg": "Preparing breakfast", 
    "name": "__main__", 
    "pathname": "/Volumes/haibo/cloudstation/src/python/logging/json_logging.py", 
    "process": 884, 
    "processName": "MainProcess", 
    "relativeCreated": 0.5948543548583984, 
    "thread": 140735977423808, 
    "threadName": "MainThread"
},
{
    "args": [], 
    "created": 1504232368.015089, 
    "exc_info": null, 
    "exc_text": null, 
    "filename": "json_logging.py", 
    "funcName": "main", 
    "levelname": "WARNING", 
    "levelno": 30, 
    "lineno": 52, 
    "module": "json_logging", 
    "msecs": 15.089035034179688, 
    "msg": "Almost out of coffee", 
    "name": "__main__", 
    "pathname": "/Volumes/haibo/cloudstation/src/python/logging/json_logging.py", 
    "process": 884, 
    "processName": "MainProcess", 
    "relativeCreated": 0.8299350738525391, 
    "thread": 140735977423808, 
    "threadName": "MainThread"
},
{
    "args": [
        "out of milk", 
        51, 
        "cow.java"
    ], 
    "created": 1504232368.0153, 
    "exc_info": null, 
    "exc_text": null, 
    "filename": "json_logging.py", 
    "funcName": "main", 
    "levelname": "ERROR", 
    "levelno": 40, 
    "lineno": 53, 
    "module": "json_logging", 
    "msecs": 15.30003547668457, 
    "msg": "error: %s in line %d, file %s", 
    "name": "__main__", 
    "pathname": "/Volumes/haibo/cloudstation/src/python/logging/json_logging.py", 
    "process": 884, 
    "processName": "MainProcess", 
    "relativeCreated": 1.0409355163574219, 
    "thread": 140735977423808, 
    "threadName": "MainThread"
},
{
    "args": [], 
    "created": 1504232368.015451, 
    "exc_info": null, 
    "exc_text": null, 
    "filename": "json_logging.py", 
    "funcName": "main", 
    "levelname": "DEBUG", 
    "levelno": 10, 
    "lineno": 54, 
    "module": "json_logging", 
    "msecs": 15.45095443725586, 
    "msg": "This is debug", 
    "name": "__main__", 
    "pathname": "/Volumes/haibo/cloudstation/src/python/logging/json_logging.py", 
    "process": 884, 
    "processName": "MainProcess", 
    "relativeCreated": 1.191854476928711, 
    "thread": 140735977423808, 
    "threadName": "MainThread"
}
]