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Logging

Scrapy provides a logging facility which can be used through the :mod:`scrapy.log` module. The current underling implementation uses Twisted logging but this may change in the future.

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Logging service must be explicitly started through the :func:`scrapy.log.start` function.

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Log levels

Scrapy provides 5 logging levels:

:data:`~scrapy.log.CRITICAL` - for critical errors

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:data:`~scrapy.log.ERROR` - for regular errors

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:data:`~scrapy.log.WARNING` - for warning messages

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:data:`~scrapy.log.INFO` - for informational messages

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:data:`~scrapy.log.DEBUG` - for debugging messages

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How to set the log level

You can set the log level using the --loglevel/-L command line option, or using the :setting:`LOG_LEVEL` setting.

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How to log messages

Here's a quick example of how to log a message using the WARNING level:

from scrapy import log
log.msg("This is a warning", level=log.WARNING)

Logging from Spiders

The recommended way to log from spiders is by using the Spider :meth:`~scrapy.spider.BaseSpider.log` method, which already populates the domain argument of the :func:`scrapy.log.msg` function. The other arguments are passed directly to the :func:`~scrapy.log.msg` function.

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scrapy.log module

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.. module:: scrapy.log
   :synopsis: Logging facility

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.. attribute:: log_level

   The current log level being used

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.. attribute:: started

   A boolean which is ``True`` is logging has been started or ``False`` otherwise.

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.. function:: start(logfile=None, loglevel=None, logstdout=None)

    Start the logging facility. This must be called before actually logging any
    messages. Otherwise, messages logged before this call will get lost.

    :param logfile: the file path to use for logging output. If omitted, the
        :setting:`LOG_FILE` setting will be used. If both are ``None``, the log
        will be sent to standard error.
    :type logfile: str

    :param loglevel: the minimum logging level to log. Availables values are:
        :data:`CRITICAL`, :data:`ERROR`, :data:`WARNING`, :data:`INFO` and
        :data:`DEBUG`.

    :param logstdout: if ``True``, all standard output (and error) of your
        application will be logged instead. For example if you "print 'hello'"
        it will appear in the Scrapy log. If ommited, the :setting:`LOG_STDOUT`
        setting will be used.
    :type logstdout: boolean

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.. function:: msg(message, level=INFO, component=BOT_NAME, domain=None)

    Log a message

    :param message: the message to log
    :type message: str

    :param level: the log level for this message. See
        :ref:`topics-logging-levels`.

    :param component: the component to use for logging, it defaults to
        :setting:`BOT_NAME`
    :type component: str

    :param domain: the spider domain to use for logging this message. This
        parameter should always be used when logging things related to a
        particular spider.
    :type domain: str

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.. function:: exc(message, level=ERROR, component=BOT_NAME, domain=None)

    Log an exception. Similar to ``msg()`` but it also appends a stack trace
    report using `traceback.format_exc`.

    .. _traceback.format_exc: http://docs.python.org/library/traceback.html#traceback.format_exc

    It accepts the same parameters as the :func:`msg` function.

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