Flask-LogConfig 0.2.0

Flask extension for configuring Python logging module

Flask extension for configuring Python logging module.

Requirements

Compatibility

• Python 2.6

• Python 2.7

• Python 3.3

• Python 3.4

Dependencies

• Flask

• logconfig

Installation

pip install Flask-LogConfig

Quickstart

Use Flask-LogConfig to easily configure the Python logging module using your Flask app’s config object:

import flask
from flask.ext.logconfig import LogConfig

class MyConfig(object):
    LOGGING = {
        'version': 1,
        'disable_existing_loggers': False,
        'formatters': {
            'simple': {
                '()': 'myapp.logging.simple_formatter_factory'
            },
            'email': {
                '()': 'myapp.logging.email_formatter_factory'
            }
        },
        'filters': {
            'email': {
                '()': 'myapp.logging.RequestFilter'
            }
        },
        'handlers': {
            'smtp': {
                'class': 'logging.handlers.SMTPHandler',
                'level': 'ERROR',
                'formatter': 'email',
                'filters': ['email'],
                'mailhost': ('example.com', 587),
                'fromaddr': 'Mailer <[e-mail]>',
                'toaddrs': ['[e-mail]'],
                'subject': 'Application Error',
                'credentials': ('[e-mail]', 'password'),
                'secure': ()
            },
            'console': {
                'class': 'logging.StreamHandler',
                'level': 'DEBUG',
                'formatter': 'simple',
                'stream': 'ext://sys.stderr'
            }
        },
        'loggers': {
            'myapp': {
                'handlers': ['smtp', 'console'],
                'level': 'DEBUG'
            }
        }
    }

    LOGGING_QUEUE = ['myapp']

app = flask.Flask(__name__)
app.config.from_object(MyConfig)
logcfg = LogConfig(app)

# or using lazy instantiation
logcfg = LogConfig()
logcfg.init_app(app)

Configuration

Configuration of Python’s logging module is specified using the standard dictConfig or fileConfig formats supported by logging.config. This allows Flaks apps to be configured as one would in a Django app that uses logging.

LOGGING

The main configuration option for Flask-LogConfig is LOGGING. This option can either be a dict or a pathname to a configuration file. The format of the dict or config file must follow the format supported by logging.config.dictConfig or loging.config.fileConfig. See Logging Configuration for more details. If using a pathname, the supported file formats are JSON, YAML, and ConfigParser.

LOGGING_QUEUE

The purpose of LOGGING_QUEUE is to provide an easy way to utilize logging without blocking the main thread.

To set up a basic logging queue, specify the loggers you want to queuify by setting LOGGING_QUEUE to a list of the logger names (as strings). These loggers will have their handlers moved to a queue which will then be managed by a queue handler and listener, one per logger.

Each logger’s queue handler will be an instance of flask_logconfig.FlaskQueueHandler which is an extension of logging.handlers.QueueHandler (back ported to Python 2 via logutils). FlaskQueueHandler adds a copy of the current request context to the log record so that the queuified log handlers can access any Flask request globals outside of the normal request context (i.e. inside the listener thread) via flask_logconfig.request_context_from_record. The queue listener used is an instance of logconfig.QueueListener that extends logging.handlers.QueueListener with proper support for respecting a handler’s log level (i.e. logging.handlers.QueueListener delegates all log records to a handler even if that handler’s log level is set higher than the log record’s while logconfig.QueueListener does not).

After the log handlers are queuified, their listener thread will be started automatically unless you specify otherwise. You can access the listeners via the LogConfig instance:

logcfg = LogConfig()

# start_listeners=True by default
logcfg.init_app(app, start_listeners=False)

assert isinstance(logcfg, list)

# start listeners manually
logcfg.start_listeners()

# stop listeners
logcfg.stop_listeners()

Log Record Request Context

When using LOGGING_QUEUE, accessing Flask’s request globals from within a log handler requires using the request context that is attached to the emitted log record.

Below is an example that uses a logging Filter to attach the request environment to the log record using flask_logconfig.request_context_from_record:

import logging
from pprint import pformat
from flask import request

from flask_logconfig import request_context_from_record

class RequestFilter(logging.Filter):
    """Impart contextual information related to Flask HTTP request."""
    def filter(self, record):
        """Attach request contextual information to log record."""
        with request_context_from_record(record):
            record.environ_info = request.environ.copy()
            record.environ_text = pformat(record.environ_info)
        return True

It’s also safe to use request_context_from_record from directly inside Flask’s request context:

with request_context_from_record():
    # do something using Flask request globals
    pass

If no request context exists (either on the log record provided or inside the actual Flask request context), then a flask_logconfig.FlaskLogConfigException will be thrown.