This document describes the current stable version of Celery (5.6). For development docs, go here.

# Source code for celery.app.log

    """Logging configuration.

    The Celery instances logging section: ``Celery.log``.

    Sets up logging for the worker and other programs,
    redirects standard outs, colors log output, patches logging
    related compatibility fixes, and so on.
    """
    import logging
    import os
    import sys
    import warnings
    from logging.handlers import WatchedFileHandler

    from kombu.utils.encoding import set_default_encoding_file

    from celery import signals
    from celery._state import get_current_task
    from celery.exceptions import CDeprecationWarning, CPendingDeprecationWarning
    from celery.local import class_property
    from celery.platforms import isatty
    from celery.utils.log import (ColorFormatter, LoggingProxy, get_logger, get_multiprocessing_logger, mlevel,
                                  reset_multiprocessing_logger)
    from celery.utils.nodenames import node_format
    from celery.utils.term import colored

    __all__ = ('TaskFormatter', 'Logging')

    MP_LOG = os.environ.get('MP_LOG', False)

    class TaskFormatter(ColorFormatter):
        """Formatter for tasks, adding the task name and id."""

        def format(self, record):
            task = get_current_task()
            if task and task.request:
                record.__dict__.update(task_id=task.request.id,
                                       task_name=task.name)
            else:
                record.__dict__.setdefault('task_name', '???')
                record.__dict__.setdefault('task_id', '???')
            return super().format(record)

    class Logging:
        """Application logging setup (app.log)."""

        #: The logging subsystem is only configured once per process.
        #: setup_logging_subsystem sets this flag, and subsequent calls
        #: will do nothing.
        _setup = False

        def __init__(self, app):
            self.app = app
            self.loglevel = mlevel(logging.WARN)
            self.format = self.app.conf.worker_log_format
            self.task_format = self.app.conf.worker_task_log_format
            self.colorize = self.app.conf.worker_log_color

        def setup(self, loglevel=None, logfile=None, redirect_stdouts=False,
                  redirect_level='WARNING', colorize=None, hostname=None):
            loglevel = mlevel(loglevel)
            handled = self.setup_logging_subsystem(
                loglevel, logfile, colorize=colorize, hostname=hostname,
            )
            if not handled and redirect_stdouts:
                self.redirect_stdouts(redirect_level)
            os.environ.update(
                CELERY_LOG_LEVEL=str(loglevel) if loglevel else '',
                CELERY_LOG_FILE=str(logfile) if logfile else '',
            )
            warnings.filterwarnings('always', category=CDeprecationWarning)
            warnings.filterwarnings('always', category=CPendingDeprecationWarning)
            logging.captureWarnings(True)
            return handled

        def redirect_stdouts(self, loglevel=None, name='celery.redirected'):
            self.redirect_stdouts_to_logger(
                get_logger(name), loglevel=loglevel
            )
            os.environ.update(
                CELERY_LOG_REDIRECT='1',
                CELERY_LOG_REDIRECT_LEVEL=str(loglevel or ''),
            )

        def setup_logging_subsystem(self, loglevel=None, logfile=None, format=None,
                                    colorize=None, hostname=None, **kwargs):
            if self.already_setup:
                return
            if logfile and hostname:
                logfile = node_format(logfile, hostname)
            Logging._setup = True
            loglevel = mlevel(loglevel or self.loglevel)
            format = format or self.format
            colorize = self.supports_color(colorize, logfile)
            reset_multiprocessing_logger()
            receivers = signals.setup_logging.send(
                sender=None, loglevel=loglevel, logfile=logfile,
                format=format, colorize=colorize,
            )

            if not receivers:
                root = logging.getLogger()

                if self.app.conf.worker_hijack_root_logger:
                    root.handlers = []
                    get_logger('celery').handlers = []
                    get_logger('celery.task').handlers = []
                    get_logger('celery.redirected').handlers = []

                # Configure root logger
                self._configure_logger(
                    root, logfile, loglevel, format, colorize, **kwargs
                )

                # Configure the multiprocessing logger
                self._configure_logger(
                    get_multiprocessing_logger(),
                    logfile, loglevel if MP_LOG else logging.ERROR,
                    format, colorize, **kwargs
                )

                signals.after_setup_logger.send(
                    sender=None, logger=root,
                    loglevel=loglevel, logfile=logfile,
                    format=format, colorize=colorize,
                )

                # then setup the root task logger.
                self.setup_task_loggers(loglevel, logfile, colorize=colorize)

            try:
                stream = logging.getLogger().handlers[0].stream
            except (AttributeError, IndexError):
                pass
            else:
                set_default_encoding_file(stream)

            # This is a hack for multiprocessing's fork+exec, so that
            # logging before Process.run works.
            logfile_name = logfile if isinstance(logfile, str) else ''
            os.environ.update(_MP_FORK_LOGLEVEL_=str(loglevel),
                              _MP_FORK_LOGFILE_=logfile_name,
                              _MP_FORK_LOGFORMAT_=format)
            return receivers

        def _configure_logger(self, logger, logfile, loglevel,
                              format, colorize, **kwargs):
            if logger is not None:
                self.setup_handlers(logger, logfile, format,
                                    colorize, **kwargs)
                if loglevel:
                    logger.setLevel(loglevel)

        def setup_task_loggers(self, loglevel=None, logfile=None, format=None,
                               colorize=None, propagate=False, **kwargs):
            """Setup the task logger.

            If `logfile` is not specified, then `sys.stderr` is used.

            Will return the base task logger object.
            """
            loglevel = mlevel(loglevel or self.loglevel)
            format = format or self.task_format
            colorize = self.supports_color(colorize, logfile)

            logger = self.setup_handlers(
                get_logger('celery.task'),
                logfile, format, colorize,
                formatter=TaskFormatter, **kwargs
            )
            logger.setLevel(loglevel)
            # this is an int for some reason, better to not question why.
            logger.propagate = int(propagate)
            signals.after_setup_task_logger.send(
                sender=None, logger=logger,
                loglevel=loglevel, logfile=logfile,
                format=format, colorize=colorize,
            )
            return logger

        def redirect_stdouts_to_logger(self, logger, loglevel=None,
                                       stdout=True, stderr=True):
            """Redirect :class:`sys.stdout` and :class:`sys.stderr` to logger.

            Arguments:
                logger (logging.Logger): Logger instance to redirect to.
                loglevel (int, str): The loglevel redirected message
                    will be logged as.
            """
            proxy = LoggingProxy(logger, loglevel)
            if stdout:
                sys.stdout = proxy
            if stderr:
                sys.stderr = proxy
            return proxy

        def supports_color(self, colorize=None, logfile=None):
            colorize = self.colorize if colorize is None else colorize
            if self.app.IS_WINDOWS:
                # Windows does not support ANSI color codes.
                return False
            if colorize or colorize is None:
                # Only use color if there's no active log file
                # and stderr is an actual terminal.
                return logfile is None and isatty(sys.stderr)
            return colorize

        def colored(self, logfile=None, enabled=None):
            return colored(enabled=self.supports_color(enabled, logfile))

        def setup_handlers(self, logger, logfile, format, colorize,
                           formatter=ColorFormatter, **kwargs):
            if self._is_configured(logger):
                return logger
            handler = self._detect_handler(logfile)
            handler.setFormatter(formatter(format, use_color=colorize))
            logger.addHandler(handler)
            return logger

        def _detect_handler(self, logfile=None):
            """Create handler from filename, an open stream or `None` (stderr)."""
            logfile = sys.__stderr__ if logfile is None else logfile
            if hasattr(logfile, 'write'):
                return logging.StreamHandler(logfile)
            return WatchedFileHandler(logfile, encoding='utf-8')

        def _has_handler(self, logger):
            return any(
                not isinstance(h, logging.NullHandler)
                for h in logger.handlers or []
            )

        def _is_configured(self, logger):
            return self._has_handler(logger) and not getattr(
                logger, '_rudimentary_setup', False)

        def get_default_logger(self, name='celery', **kwargs):
            return get_logger(name)

        @class_property
        def already_setup(self):
            return self._setup

        @already_setup.setter
        def already_setup(self, was_setup):
            self._setup = was_setup