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Flask extension for configuring Python logging module.



  • Python 2.6
  • Python 2.7
  • Python 3.3
  • Python 3.4



pip install Flask-LogConfig


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):
        '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 <mailer@example.com>',
                'toaddrs': ['admins@example.com'],
                'subject': 'Application Error',
                'credentials': ('mailer@example.com', 'password'),
                'secure': ()
            'console': {
                'class': 'logging.StreamHandler',
                'level': 'DEBUG',
                'formatter': 'simple',
                'stream': 'ext://sys.stderr'
        'loggers': {
            'myapp': {
                'handlers': ['smtp', 'console'],
                'level': 'DEBUG'

    LOGCONFIG_QUEUE = ['myapp']

app = flask.Flask(__name__)
logcfg = LogConfig(app)

# or using lazy instantiation
logcfg = LogConfig()


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


The main configuration option for Flask-LogConfig is LOGCONFIG. 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.


The purpose of LOGCONFIG_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 LOGCONFIG_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

# stop listeners

See the Log Record Request Context section for details on accessing an application’s request context from within a queue.


When set to True, LOGCONFIG_REQUESTS_ENABLED turns on logging for all requests. Defaults to False.

Requests will be logged at the end of the request via the app.after_request hook. In addition to providing a custom log msg, additional extra arguments will be passed to the logging call:

  • response
  • request

These can later be accessed from the log record via record.response and record.request. This provides a convenient way for the log filters, handlers, and formatters to access request/response specific data.


The logger name to use when logging all requests. Defaults to None which uses app.logger.


The log level at which to log all requests. Defaults to logging.DEBUG.


The message format used to generate the msg argument to log() when logging all requests. Defaults to '{method} {path} - {status_code}'.

When generating the message, LOGCONFIG_REQUESTS_MSG_FORMAT.format(**kargs) will be called with the following keyword arguments:

From request.environ


NOTE: Additional data may be available depending on the WSGI environment provided.

From request

  • method
  • path
  • base_url
  • url
  • remote_addr
  • user_agent

From response

  • status_code
  • status

From flask

  • session

NOTE: The session argument is a computed as follows:

from collections import defaultdict
from flask import session

session_data = defaultdict(lambda: None)

This means that you can safely access session values even if they aren’t explictly set. When they are missing, None will be returned instead.

From computed

  • execution_time (in milliseconds) NOTE: This is the time between the start of the request and then end.

Log Record Request Context

When using LOGCONFIG_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

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.

API Reference

Includes links to source code.

Project Info

Indices and tables