Pylons - An Overview: Rapid MVC Web Development with WSGI
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A simple overview of Pylons given at the Cambridge Python Meetup Group in January of '08. From the 0.9.6 era, it's basically outdated by now, but I wanted to archive it on Slideshare. The complete presentation has a lot of notes. The example application discussed was QuickWiki, the standard Pylons tutorial app.
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Pylons - An Overview: Rapid MVC Web Development with WSGI
- 1. Pylons - An Overview Rapid MVC Web Development with WSGI Ches Martin ches.martin@gmail.com Friday, March 20, 2009
- 2. Background What Brought Me Here : Friday, March 20, 2009
- 3. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language Friday, March 20, 2009
- 4. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language • didn't always like the more quot;opinionatedquot; approaches of the NIH frameworks... Friday, March 20, 2009
- 5. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language • didn't always like the more quot;opinionatedquot; approaches of the NIH frameworks... • sometimes convention-over-configuration goes too far Friday, March 20, 2009
- 6. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language • didn't always like the more quot;opinionatedquot; approaches of the NIH frameworks... • sometimes convention-over-configuration goes too far • interested in Python for some time Friday, March 20, 2009
- 7. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language • didn't always like the more quot;opinionatedquot; approaches of the NIH frameworks... • sometimes convention-over-configuration goes too far • interested in Python for some time • All those fanboys grate on my nerves Friday, March 20, 2009
- 8. Background What Brought Me Here : • wanted a rapid-development MVC web framework in a dynamic language • didn't always like the more quot;opinionatedquot; approaches of the NIH frameworks... • sometimes convention-over-configuration goes too far • interested in Python for some time • All those fanboys grate on my nerves • I'm subversive by nature ;-) Friday, March 20, 2009
- 9. Why Pylons? Friday, March 20, 2009
- 10. What It Is: • Flexible, Modular, Extensible • Active • Largely built on established libraries • A community of Python whizzes • Forward-thinking • The foundation of TurboGears 2.0 Friday, March 20, 2009
- 11. What It Isn't Friday, March 20, 2009
- 12. What It Isn't • 1.0 • The framework components that it builds -- and sometimes more significantly, the on -- are still moving targets at times Friday, March 20, 2009
- 13. What It Isn't • 1.0 • The framework components that it builds -- and sometimes more significantly, the on -- are still moving targets at times • A CMS Friday, March 20, 2009
- 14. What It Isn't • 1.0 • The framework components that it builds -- and sometimes more significantly, the on -- are still moving targets at times • A CMS • A cakewalk. • Fewer decisions made for you -- you’ll spend time learning your way around Friday, March 20, 2009
- 15. A Brief History • Who's Who • HTML::Mason => Myghty + Paste, dash of Rails => Pylons, Mako, Beaker, etc. Friday, March 20, 2009
- 16. Concepts and Architecture Friday, March 20, 2009
- 17. WSGI (Web Server Gateway Interface) Friday, March 20, 2009
- 18. What is WSGI? • Specifies standard interface between web servers and Python web apps • Goal of decoupling app implementation from specific web servers • PEP 333 - reference implementation in Python 2.5 standard lib • quick look at the interface with environ & start_response • Paste (and PasteScript, PasteDeploy) Friday, March 20, 2009
- 19. Why Should You Care About It? • 'onion model' of layered, independent middleware components • implements both “sides” of WSGI spec: looks like an app to a server, and a server to an app • intercept and transform responses and requests as they move through the chain • can do exception handling, things like authentication, etc. • yes, this means you could quot;embedquot; or quot;wrapquot; a Pylons app within another Pylons app Friday, March 20, 2009
- 20. WSGI Hello World def my_app(environ, start_response): start_response('200 OK', [('Content-type', 'text/html')]) return ['<html><body>Hello World!</body></html>'] • start_response() is called with a status code and list of tuple pairs for headers before it returns a value and should be called only once • environ is a dict of CGI-style variables • The response is an iterable Friday, March 20, 2009
- 21. Framework Components • URL Dispatch (Routes) • Object-Relational Mapper / DB Abstraction • Template Engine (Mako) • Sessions Management / Caching (Beaker) • Form Handling / Validation (FormEncode) • WebHelpers Friday, March 20, 2009
- 22. An Example Application Friday, March 20, 2009
- 23. Deploying and Distributing Friday, March 20, 2009
- 24. Deployment Options • The great advantage of eggs / setuptools / PasteDeploy • Paste's http server • mod_wsgi • Twisted • even mod_python, with a WSGI gateway • AJP • Process Control options Friday, March 20, 2009
- 25. Web Service Conveniences • Special controllers for REST & XML-RPC • map.resource, for generating RESTful routes • JSON: simplejson and @jsonify decorator • enhanced content negotiation and mimetype support forthcoming in 0.9.7 Friday, March 20, 2009
- 26. map.resource (Routes) map.resource('message', 'messages') # Will setup all the routes as if you had typed the following map commands: map.connect('messages', controller='messages', action='create', conditions=dict(method=['POST'])) map.connect('messages', 'messages', controller='messages', action='index', conditions=dict(method=['GET'])) map.connect('formatted_messages', 'messages.:(format)', controller='messages', action='index', conditions=dict(method=['GET'])) map.connect('new_message', 'messages/new', controller='messages', action='new', conditions=dict(method=['GET'])) map.connect('formatted_new_message', 'messages/new.:(format)', controller='messages', action='new', conditions=dict(method=['GET'])) map.connect('messages/:id', controller='messages', action='update', conditions=dict(method=['PUT'])) map.connect('messages/:id', controller='messages', action='delete', conditions=dict(method=['DELETE'])) map.connect('edit_message', 'messages/:(id);edit', controller='messages', action='edit', conditions=dict(method=['GET'])) map.connect('formatted_edit_message', 'messages/:(id).:(format);edit', controller='messages', action='edit', conditions=dict(method=['GET'])) map.connect('message', 'messages/:id', controller='messages', action='show', conditions=dict(method=['GET'])) map.connect('formatted_message', 'messages/:(id).:(format)', controller='messages', action='show', conditions=dict(method=['GET'])) Friday, March 20, 2009
- 27. Extras • Interactive debugger; ipython for paster shell • Unicode throughout, developers strongly concerned with i18n • Excellent logging framework; Chainsaw • Testing: Nose, paste.fixture's request simulation • Paste templates, scripts; Tesla Friday, March 20, 2009
- 28. Other Extras • Elixir; declarative layer for SQLA following Martin Fowler's Active Record pattern (Rails) • Authkit • ToscaWidgets • doc generation; Pudge, Apydia • Migrate for SQLAlchemy, adminpylon, dbsprockets Friday, March 20, 2009
- 29. Links Friday, March 20, 2009
- 30. Pylons • Home Page: http://pylonshq.com/ • IRC: #pylons on irc.freenode.net • Mailing List: http://groups.google.com/group/pylons-discuss • Mercurial (version control): https://www.knowledgetap.com/hg/ Friday, March 20, 2009
Notes de l'éditeur
- Disclaimer: I haven't built any sort of large-scale, high-traffic Pylons app, nor gotten rich from it. Hire me and let's build one :-) Thanks for George's coverage of HTTP protocol in his mod_python talk in December
- Rails, Django; use existing libraries, please! Reasons of philosophy don't want to bash Django -- all in all I think it's a nice framework and good for Python. I make comparisons because I assume that many are familiar with it Ruby can be a little Perl-like, which should scare you. Also so many DSLs and metaprogramming makes me worry about the Law of Leaky Abstractions...
- WSGI to the core, setuptools
- The developers of the central pieces are working closely together, and mostly try not to break APIs in major ways Not much in the way of off-the-shelf apps yet. It's not Plone, there are not built-in widgets or a spiffy auto-admin like Django You will spend some time getting familiar with the components and what does what. Fewer decisions are made for you -- flexibility comes at the cost of doing some homework and having ideas about what you want before diving in. As always, use the right tool for the job.
- Ben Bangert - Lead Dev, O’Reilly Pylons, Routes, Beaker, WebHelpers Mike Bayer - Myghty, Beaker, Mako, SQLAlchemy Ian Bicking - Paste, FormEncode, virtual/workingenv
- Flexible deployment options, ability to jump ship to a different server architecture Paste is essentially a WSGI toolkit. Provides conveniences for lower-level WSGI apps or rolling your own framework. Pylons builds on Paste in much the same way that TurboGears 1.0 built on CherryPy.
- mostly lifted from Ben Bangert’s Google Tech Talk presentation on Pylons and WSGI: http://www.groovie.org/articles/2006/09/18/wsgi-paste-pylons-and-all-that
- Pylons includes Routes, also a Ben Bangert project; ported from Rails, but extended and moving in its own directions. Fairly popular outside of Pylons. Briefly compare versus CherryPy/Zope object publishing and Django's regular expressions. Pylons is agnostic, but SQLAlchemy is the overwhelming community favorite. Recipes are available for using Storm, Schevo (pure-Python, non-SQL DBMS), probably Geniusql, CouchDB Pylons default is the excellent Mako, developed by Michael Bayer as a derivation of Myghty's templating system. Buffet-compatible engines are easily swapped in, or used in tandem. This includes Genshi, Cheetah, Kid, Myghty, Jinja (Django-style). XML- or predefined tag-based versus Python-like syntax and inheritance model. Beaker (with Middleware). Caching supported in memory, filesystem and memcached. Signed cookies, and support for cookie-only sessions. FormEncode - validates and coerces to Python types. Touch on form generation / widget tools like ToscaWidgets, FormBuild, FormAlchemy. Helpers for common tasks like text operations (datetime formatting, Textile / Markdown), RSS, and form and URL tags. The latter require Routes and protect your templates from changes in URL structure. Also Javascript integration with Prototype and Scriptaculous, which may eventually disappear from WebHelpers.
- In this case we can even show Pylons installation, and suggest it as a best practice Point out that QuickWiki basically uses the default Routes. We can look at more example Routes definitions when discussing map.resource and REST.
- setuptools, PasteDeploy how an end user would install and run the app daemon mode, process management options 'entry points' facilitate plugin development Paste HTTP server thread-pooling substitute CherryPy's with one config file directive reverse-proxy with Apache, lighttpd, nginx, etc. Process control Monit, daemontools, supervisord, God
- Debug in Wing: wingware.com—paste-pylons <http://wingware.com/doc/howtos/paste-pylons> internationalization, and \"smart\" resources that might serve, say, XHTML and JSON
- Although recall my concerns about the Law of Leaky Abstractions -- while Elixir may seem simpler, it may actually prove more complex to debug.