Logging
-------

.. versionadded:: 0.3

Sometimes you might be in a situation where you deal with data that
should be correct, but actually is not.  For example you may have some client-side
code that sends an HTTP request to the server but it's obviously
malformed.  This might be caused by a user tampering with the data, or the
client code failing.  Most of the time it's okay to reply with ``400 Bad
Request`` in that situation, but sometimes that won't do and the code has
to continue working.

You may still want to log that something fishy happened.  This is where
loggers come in handy.  As of Flask 0.3 a logger is preconfigured for you
to use.

Here are some example log calls::

    app.logger.debug('A value for debugging')
    app.logger.warning('A warning occurred (%d apples)', 42)
    app.logger.error('An error occurred')

The attached :attr:`~flask.Flask.logger` is a standard logging
:class:`~logging.Logger`, so head over to the official `logging
documentation <https://docs.python.org/library/logging.html>`_ for more
information.

Read more on :ref:`application-errors`.