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16: Collecting Application Info With Logging

Capture debugging and error output from your web applications using standard Python logging.

Background

It's important to know what is going on inside our web application. In development we might need to collect some output. In production, we might need to detect problems when other people use the site. We need logging.

Fortunately Pyramid uses the normal Python approach to logging. The scaffold generated, in your development.ini, has a number of lines that configure the logging for you to some reasonable defaults. You then see messages sent by Pyramid (for example, when a new request comes in.)

Objectives

  • Inspect the configuration setup used for logging
  • Add logging statements to your view code

Steps

  1. First we copy the results of the view_classes step:

    $ cd ..; cp -r view_classes logging; cd logging
    $ $VENV/bin/python setup.py develop
    
  2. Extend logging/tutorial/views.py to log a message:

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    import logging
    log = logging.getLogger(__name__)
    
    from pyramid.view import (
        view_config,
        view_defaults
        )
    
    
    @view_defaults(renderer='home.pt')
    class TutorialViews:
        def __init__(self, request):
            self.request = request
    
        @view_config(route_name='home')
        def home(self):
            log.debug('In home view')
            return {'name': 'Home View'}
    
        @view_config(route_name='hello')
        def hello(self):
            log.debug('In hello view')
            return {'name': 'Hello View'}
    
  3. Make sure the tests still pass:

    $ $VENV/bin/nosetests tutorial
    
  4. Run your Pyramid application with:

    $ $VENV/bin/pserve development.ini --reload
    
  5. Open http://localhost:6543/ and http://localhost:6543/howdy in your browser. Note, both in the console and in the debug toolbar, the message that you logged.

Analysis

Our development.ini configuration file wires up Python standard logging for our Pyramid application:

[app:main]
use = egg:tutorial
pyramid.reload_templates = true
pyramid.includes =
    pyramid_debugtoolbar

[server:main]
use = egg:pyramid#wsgiref
host = 0.0.0.0
port = 6543

# Begin logging configuration

[loggers]
keys = root, tutorial

[logger_tutorial]
level = DEBUG
handlers =
qualname = tutorial

[handlers]
keys = console

[formatters]
keys = generic

[logger_root]
level = INFO
handlers = console

[handler_console]
class = StreamHandler
args = (sys.stderr,)
level = NOTSET
formatter = generic

[formatter_generic]
format = %(asctime)s %(levelname)-5.5s [%(name)s][%(threadName)s] %(message)s

# End logging configuration

In this, our tutorial Python package is setup as a logger and configured to log messages at a DEBUG or higher level. When you visit http://localhost:6543 your console will now show:

2013-08-09 10:42:42,968 DEBUG [tutorial.views][MainThread] In home view

Also, if you have configured your Pyramid application to use the pyramid_debugtoolbar, logging statements appear in one of its menus.

See also

See also Logging.

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