Some documentation updates

Author: mitsuhiko

docs/logging.rst

@@ -56,4 +56,130 @@ This document only specifies a logbook setup.  If you are interested in
 the documentation for the old logging system, have a look at
 :ref:`old-logging`.
 
+Making the Switch
+-----------------
+
+The default configuration of Logbook is fine and Flask even adds a small
+little improvement on top of that.  However you currently have to opt-in
+for Logbook support::
+
+    from flask import Flask
+    app = Flask(__name__, logging_system='logbook')
+
+The other options for the logging system are:
+
+``'logging'``
+    Deprecated support for logging to the logging system.
+
+``'logbook'``
+    Logging to `Logbook`_, requires that the library is installed.
+
+``'none'``
+    Configure a dummy logger for internal usage but do not set up a
+    real logging system.
+
+In Flask 1.0 the logging system parameter will become a no-op and Logbook
+will always be used.  In case Logbook is not installed in 1.0 and later,
+it will dynamically fall back to the dummy logger which currently is not
+the case.
+
+Logging Messages
+----------------
+
+If you have used logging before in Flask applications you will have used
+the :attr:`~flask.Flask.logger` attribute.  While that is nice and you can
+continue to use this logger, it is recommended to use a logger for logging
+directly.  The reason for this is that you have better control over what
+you are doing and can shut down a logger completely to reduce runtime
+overhead.
+
+To make the switch, replace calls to this::
+
+    @app.route('/')
+    def index():
+        app.logger.warn('A message')
+        ...
+
+With something like this::
+
+    from logbook import Logger
+    logger = Logger('My component')
+
+    @app.route('/')
+    def index():
+        logger.warn('A message')
+        ...
+
+Note that Logbook is using Python 2.6's new string formatting feature
+instead of the printf style string formatting that was in use by logging::
+
+    app.logger.warn('Hello %s!', name)
+
+Becomes this now::
+
+    app.logger.warn('Hello {0}!', name)
+
+You can also use named parameters::
+
+    app.logger.warn('Hello {name}!', name=name)
+
+Logbook ships with a pure Python implementation of the new string
+formatting for Python 2.5 which is why it is recommended to use Python 2.6
+in case you are doing a lot of logging calls that are delivered to
+handlers in production.  It will of course not affect logging calls that
+don't happen because their level is too low (like debug log calls on a
+production system that only cares about warnings and higher priority
+records).
+
+Consult the `Logbook documentation`_ for more information.
+
+Error Mails
+-----------
+
+If the application runs in production mode (which it will do on your
+server) you won't see any log messages by default.  Why is that?  Flask
+tries to be a zero-configuration framework.  Where should it drop the logs
+for you if there is no configuration?  Guessing is not a good idea because
+chances are, the place it guessed is not the place where the user has
+permission to create a logfile.  Also, for most small applications nobody
+will look at the logs anyways.
+
+In fact, I promise you right now that if you configure a logfile for the
+application errors you will never look at it except for debugging an issue
+when a user reported it for you.  What you want instead is a mail the
+second the exception happened.  Then you get an alert and you can do
+something about it.
+
+Flask uses the Python builtin logging system, and it can actually send
+you mails for errors which is probably what you want.  Here is how you can
+configure the Flask logger to send you mails for exceptions::
+
+    ADMINS = ['[email protected]']
+    if not app.debug:
+        import logging
+        from logging.handlers import SMTPHandler
+        mail_handler = SMTPHandler('127.0.0.1',
+                                   '[email protected]',
+                                   ADMINS, 'YourApplication Failed')
+        mail_handler.setLevel(logging.ERROR)
+        app.logger.addHandler(mail_handler)
+
+So what just happened?  We created a new
+:class:`~logging.handlers.SMTPHandler` that will send mails with the mail
+server listening on ``127.0.0.1`` to all the `ADMINS` from the address
+*[email protected]* with the subject "YourApplication Failed".  If
+your mail server requires credentials, these can also be provided.  For
+that check out the documentation for the
+:class:`~logging.handlers.SMTPHandler`.
+
+We also tell the handler to only send errors and more critical messages.
+Because we certainly don't want to get a mail for warnings or other
+useless logs that might happen during request handling.
+
+Before you run that in production, please also look at :ref:`logformat` to
+put more information into that error mail.  That will save you from a lot
+of frustration.
+
+
 .. _Logbook: http://logbook.pocoo.org/
+.. _Logbook documentation: http://logbook.pocoo.org/

flask/app.py

@@ -173,7 +173,7 @@ class Flask(_PackageBoundObject):
     logger_name = ConfigAttribute('LOGGER_NAME')
 
     #: the logbook setup that should be in use.  This is only used in case
-    #: the `LOGGING_SYSTEM` is ``'logbook'``.  It can point to any
+    #: the logging system is ``'logbook'``.  It can point to any
     #: :class:`logbook.Processor`, :class:`logbook.Handler` or
     #: :class:`logbook.NestedSetup`.  In case it's `None`, the default
     #: application wide setup is used.  For further customization you can
@@ -321,7 +321,7 @@ def logger(self):
             app.logger.warning('A warning ocurred (%d apples)', 42)
             app.logger.error('An error occoured')
 
-        In case the `LOGGING_SYSTEM` is ``'logbook'`` it is strongly
+        In case the logging system is ``'logbook'`` it is strongly
         recommended against using this logger and create your own.  Unlike
         logging, logbook automatically will handle writing to the
         :attr:`logbook_setup`.