Fetchez le Python

Technical blog on the Python programming language, in a pure Frenglish style. Main topics are Python and Mozilla – This blog does not engage my employer

Tag: python

How to be disappointed with the “printed” in “printed book”

I feel really bad about this comment on my book : How To Be Dissappointed in Something You Recommend.

Just a quick word about the try, return finally code pattern, since I had some feedback about it. I would like to mention that this code pattern is perfectly right:

def function():
    try:
      return something
    finally:
      do something

I should have explained it better, because this pattern is not used a lot by people, so you can think that “do something” is called after the return of the function, which is not the case.

For the typos now:

The first thing I did wrong: when I started the book, I wanted, as I did in my previous book, to run unit tests on the book itself to avoid those mistakes. That said, the previous one was in Latex, which is quite simple to interact with, and this one is in OpenOffice, because that is how the editor works. I had to write a script to extract the Python code from the Ooo file, to unit test it. I didn’t. I simply ran out of time, as usual when you have deadlines on books.

The second thing I did wrong: I should have told the editor to wait a bit, I didn’t.

But Packt does Print On Demand, so I know that the Errata page I am maintaining here : http://atomisator.ziade.org/wiki/Errata, is being processed by the editor, and that the typos will be removed from the book at some point, without having to wait for a second edition.

I’ll update this blog entry as soon as I know the status on this.

I am really sorry Calvin, and all the people that are suffering from these typos.

Plone Conference 2008 in Washington D.C. – summary

I am back from the Plone Conference in D.C., and the jetlag is gone. The jetlag is gone for weeks now but it’s hard to find the time to blog these days :/

On the talks I have seen and topics I have chatted about

There were a lot of great talks in D.C., and it was hard to decide which one to look at. In any case it was easy to meet the speaker if I had missed the talk, because the Plone Conference, unlike big conferences like OSCON, is a place where everyone hangs around the same spot after a talk is over.

Here’s a list of some topics I have seen or I have talked about with some people.

Deliverance – Ian Bicking

If you look at what Ian has produced in the past 5 years, he is one of the most prolific contributor of tools that become standards in the Python web development web community. Think about Python Paste or virtualenv, and many others. Deliverance might be the next big one.

Take a bunch of micro web applications you want to join to build a full web system, for historical reasons or just because you believe a particular feature just won’t fit in Plone but will do great in Pylons.

Now ask a designer to glue everything together under the same look. He (or the guy that integrates his design) will probably hates you: he will have to learn how to integrate in heterogeneous environments. This is easy under some systems that let you stick a layout and a css in a simple way. This is not easy under Plone, unless you learn how to do it (but this will be improved in the future).

Deliverance is a proxy that let you skin any application that spits html content, by running some XPATH rules on the content and applying some changes to produce a new output. Basically, you have a simple html page that just provides the layout you want to have, without any content, and a xml file that explains how to extract some content from the page produced by the third-party application and where to inject it in your empty html page. The great thing is that you can call different third-party servers given the path you are in, and even call several servers to build one single page. This opens a lot of perspectives.

The first caveat of this approach is that you have to provide a Single-Sign On feature to avoid people having to connect several times. This can be a problem sometimes with some applications if they are not open enough to let you do it. But most of the time, it is not a problem : if the users are all located in a LDAP it is easiy.

Furthermore, if you use only Python-based applications, you can use a WSGI envrionment and a middleware like repoze.who to glue together let’s say, a Plone app and a Pylons app. Products.oopas is the PAS plugin that can be used for that on Plone side to grab the authentication context and use it.

The second problem I can see is about response headers. One example: if a page is composed of elements that comes from several pages, and if the page has a Last-Modifier header, I don’t think Deliverance handles this correctly yet, to make sure to present the newest Last-Modified header from all third-party servers that where called to build that page. But this more likely to be a detail compared to the single authentication problem.

In any case this is a very promising tool !

Content Mirror – Kapil Thangavelu

I didn’t see that talk, but I have talked about this tool with a few people. The idea is to serialize the content of a Plone instance into a relational database (eg Postgresql), as it happens, using events.

I need to give a try and check it deeper, to see how the overhead is dealt, and how the aggregator I have read about is doing (it collects mirorring operations to perform in a transaction, and optimize the calls at the end of the transaction to avoid redudant calls if I understood correctly). I don’t know yet for example if there’s a pool of jobs for the mirroring tasks to avoid a point of failure. But I am pretty sure this is taking care of. The other point I need to see if there’s a round trip. e.g. if there’s a way to apply a relational database change back into Plone.

But in any case I can already see various use cases for my customers. For instance, having a plone instance as a back office, with complex workflows for editors and contributors, and a lightweight Pylons application as the front application, that concentrates into displaying the relational database as fast as possible, makes a lot of sense in big environments. It just scales better.

So this is a interesting tool as well.

repoze.bfg – Chris McDonough

Chris gave a talk about repoze.bfg, which is a new web framework that takes back the good bits from Zope and push them into a WSGI world, using the Pylons approach I would say. That is : “here’s the template engine you can use in repoze, but really, use the one you like”.

Frankly, I am really seeing this new effort as one of the most promising one in the Zope community. Already, repoze.auth is a major middleware in WSGI : Zope’s Pluggable Authentication Service outside Zope, usable with any WSGI application. This is a blast !

And people are starting to contribute a lot of interesting middlewares under the repoze namespace.

Now I didn’t really try repoze.bfg itself yet, but given the people that are behind it, I am pretty sure this framework will meet success in the future. Having a MVC framework ala Pylons that let you use Zope packages with a “this zope package is repoze/wsgi compliant” label on each one of them is very cool.

collective.indexing – Andreas Zeidler and al

At the snow sprint, we worked with the Enfold crew that did a great work in integrating the Solr/Lucene system so it can be used from Plone. We replaced a few fields like the searchable text and indexed it on Solr side, just to give it a try. The snow work was really focusing on providing a buildout, a few recipes and a bench to say : “Hey, Plone community, this is a blast ! let’s do more of it”

Later Andreas Zeidler and a few other guys continued the work on indexing matter and they delivered collective.indexing, which provides two things:

  • a queue that collects all indexing to be done, and optimize the call to the catalog
  • a bridge to use collective.solr

I didn’t follow the latest development and I didn’t know how far the guys went, but I had the chance to hang around with Andreas and Tom Lazar in D.C., so now I know that this package is production ready 😀

So in other words : I’ll probably use it as a mandatory package for all the big plones out there.

The queuing part imho, should go into the catalog itself because there’s no other way to make sure a third-party product is not calling the catalog during the transaction wile another product does the same.

Server-Side Include (SSI)

Tom Lazar worked during the Snow Sprint on lovely.remoteinclude to make Plone portlets accessible via unique URLs. From there, it is possible to push a page that contains a list of urls rather than the calculated page, to a front server that knows how to read SSI directive, and builds the page.

This is great for performances, and is a lot like ESI (Edge Side Include) we use to have in CPSSkins.

I am wondering if both could be implemented in the same tool in fact.

Tom told me that he will try to continue this work at the performance sprint in Bristol in december, so let’s keep an eye on this !

I have seen many other talks and topics, but these few ones where the ones I really needed to talk about.

On the conference organization

I am helping in the organization of Pycon FR in Paris since 2 years now. I know what is means to organize such events : it is a LOT OF WORK.

You know when an event is well organized when you don’t feel it is organized.

That was the case in D.C. Bravo Alex, Amy and all the others !

The only problem (wifi) was not the organizers fault, and I have never been to any event where it is not cahotic at some point (besides OSCON) so… 🙂

On the community

I love you all guys. It is an amazing community.

Atomisator, a framework to build custom RSS feeds

We are all overwhelmed by the amount of data in our feed readers. While this problem is unavoidable if you keep on adding new feeds in it, they could be automatically filtered and categorized to reduce the flow of data.

I wanted for a long time to try out some custom filters over my feeds to find for example related entries, by trying to understand the meaning of the posts, using tools like NLTK.

So I needed a playground for this, where I could play with feeds.

I think the closest tool for this is to use Yahoo Pipes but as far as I know, the only way to create custom filters is to run a web service and call it from Yahoo Pipes.

Anyways, I started to code a framework (at first it was an example for my latest book) that looks a lot like Yahoo Pipes in its principles. I don’t have any User Interface at this time of course, but a simple plugin-based tool that will let me combine my code snippets with feeds.

It is called Atomisator (see http://atomisator.ziade.org).

The big picture

The big picture

The process is quite simple:

  1. Readers are plugins that know how to read a source and provide entries out of it.
  2. Filters are plugins that know how to remove unwanted entries, or enhance them (change their title, summary, etc.). They can be combined.
  3. the entries are then pushed in a database. This is useful to avoid doublons, and to keep track of past entries.
  4. to create the feed, the entries are read from the database
  5. Enhancers are plugins that will add to entries extra info. Typically info that can’t be stored, like Digg comments if the entry is detected on Digg, or Google related searches, and so on
  6. The feed is then generated.

Right now I am focusing on making it fast, which is not simple because the plugins can play with all entries in the database.

It is in early stage and undertested, but it kinda works. I pushed it at PyPI to see of it meets interest. If it does, I will document the process of writing plugins.

Make sure you have SQlite installed, and give it a try :

$ easy_install atomisator.main
$ atomisator -c atomisator.cfg
$ atomisator

You will have an atomisator.xml feed created. You can add other feeds in atomisator.cfg as well and try them.

Now with this environment, I can start to try out custom algorithms over my feeds.

I’ve been told the name doesn’t sound right in Ehglish, but it does in French so I keep it 😉

My OSCON slides online (zc.buildout)

After a few attempts to make my screencast look nice under Google Video, I decided I would just upload the original ones (.mov and .m4v files) and a PDF export of my presentation.

So everything is available here: http://ziade.org/oscon

Slides: http://ziade.org/oscon/oscon.pdf

The .mov files are streamed automatically in your browser I believe, not the m4v ones.

Thanks to Jim Fulton for the quick feedback.