Log Handlers dictate how the log entries are handled. For example FileHandler would allow us to pipe our logs to a file. HTTP Handler makes it possible to send the logs over HTTP to a remote server. We can write our own log handlers if we need to customize the way our logs are processed. Writing a custom handler is pretty simple. We have to subclass it from logging.Handler class and must define the emit method. This method is called with each log record so we can process it.
Here’s an exmaple of a custom log handler which POSTs the logs to a remote server using the popular requests library.
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class RequestsHandler(Handler): def emit(self, record): log_entry = self.format(record) return requests.post('http://example.com:8080/', log_entry, headers={"Content-type": "application/json"}).content |
Now we have our custom handler that will post the logs to another server. What if we want to send the message in a specific format? We write our custom formatter. A formatter has a format method which gets the record. We can take the record and return a message formatted according our need. Here’s an example for logstash format:
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class LogstashFormatter(Formatter): def __init__(self, task_name=None): self.task_name = task_name super(LogstashFormatter, self).__init__() def format(self, record): data = {'@message': record.msg, '@timestamp': datetime.datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%S.%fZ'), '@type': 'IronWorker'} if self.task_name: data['@task_name'] = self.task_name return json.dumps(data) |
So we have got ourselves a custom log handler and a formatter. But how do we use them? Here’s a short code snippet:
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def __init_logging(self): self.logger = logging.getLogger(self.logger_name.upper()) self.logger.setLevel(self.logging_level) handler = RequestsHandler() formatter = LogstashFormatter(self.logger_name.upper()) handler.setFormatter(formatter) self.logger.addHandler(handler) |