Armin Ronacher's Thoughts and Writings

Python, the Web and Little Things on my Mind

written on Saturday, January 22, 2011

A few days ago PEP 3333 was accepted. In case you don't know what this is: it's a specification of WSGI (PEP 333) updated for Python 3. In case you are wondering what it does: it basically just specifies something very close to what everybody was expecting for Python 3 anyways. Together with that also some work went into improving the standard library for Python 3.2 so that it would become easier to port applications to Python 3.

Besides that there were also some recent developments in the Python web world I would really love to share my thoughts about.

Python 3 and the Web

When I was complaining about Python 3 for web development (or more exactly WSGI) at DjangoCon Europe a year ago, I wanted to raise concern about the state of WSGI and that part of the problem was that very few people cared about it. Also I was very unhappy with the idea of introducing Unicode for parts that are clearly not intended to be Unicode. A lot of things have changed. First of all I was wrong about Unicode on the WSGI layer. While I still think that it would have been a wiser choice to stick to bytes there the environment just does not support this very well. Python 3 does not provide any useful string operations for byte objects and there is also not really a plan to support it. Furthermore a lot of places in the standard library now accept Unicode where Unicode was not necessarily the best idea. However at the same time there is also a lot of opportunity now to drive things forward. The fact that urllib on Python 3 is behaving unexpected with regard to Unicode and bytes means that we will probably see some actual working IRI libraries.

The problem there however is that a direct port of Werkzeug to Python 3 is very unlikely. To make a transition possible I would probably have to change some interfaces also for Python 2. Otherwise a painless upgrade seems to be pretty unlikely. This is a lot easier for higher level interfaces such as Flask which is based on Werkzeug. That will probably work the moment Werkzeug itself works as there is barely anything in there that would not survive a run through 2to3.

The other aspect however right now is that a port to Python 3 will take a lot of time which I am not yet willing to spend due to the low demand of users being interested in Python 3. This I think has two reasons:

  1. A switch to Python 3 is a lot of work and you don't win anything. Python 3 performs considerably worse than Python 2 (Source) for certain tasks and Python 2 already wasn't the fastest interpreter. Part of that can probably be explained with Unicode requiring more memory internally than bytestrings did (2 to 4 times as much for strings). Secondly a lot of stuff broke from Python 2 to Python 3 and due to the low number of users a lot of these issues are yet to be noticed. As with all problems in the language and standard library itself just fixing them is not a solution. To also support “older” versions of Python 3 developers will always add workarounds to their code for problems also in the standard library. That's unfortunately pretty much a chicken-egg problem.

  2. PyPy, stackless and alternative Python implementations don't have plans for Python 3 or no plans yet. For a long time CPython was the only implementation everybody cared about. However this seems to be changing. To quote Brett Cannon:

    Is this finally going to push CPython into the realm of being the reference implementation of Python with PyPy being the one everyone runs in production? And is this going to impact any potential future momentum for unladen swallow if PyPy continues to gain on speed?

    Alternative Python implementations are important because they enable web developers to use Python in environments where they couldn't otherwise use it (Jython in enterprise environments with Java requirements for instance) or because they have features that are unavailable in CPython or don't perform as well.

Python 3 is clearly the better language, hands down. The downside however is that porting existing applications is a giant step and nobody can see into the future. The big advantage of Python 3 was supposed to be Unladen Swallow but unfortunately the numbers are far from what everybody was expecting.

So let me reiterate my suggestion for Python 3 in web applications: don't use it just yet, but write your code in a way that it could pass through 2to3. It's surprisingly easy for high level applications in the web field because all frameworks already are Unicode based in Python 2. That way you have the options to go with either development (PyPy or Python 3) when one is clearly going ahead.

Personally I am looking forward to this year's PyCon where there will be most likely a bunch of discussions about the future of Python. Either way it will be bright.

A pretty depressing quote on Python 3 came from Mark Pilgrim:

Python 3 is a commercial disaster. In 2010Q3 I had negative sales of DiP3 [Dive into Python 3]. More people returned it than bought it. I'm considering retro-fitting the book's content to Python 2.7 and re-releasing it as “Dive Into Python 2.” Seriously.

At least this clearly shows that Python 3 is not going as good as it could, and that rethinking the roadmap might be a good idea.


The other thing that is constantly on my mind is the variety in frameworks, WSGI implementations and a bunch of other “competing” libraries. As far as I am concerned we are doing great, much better than before. Of course I am sitting in my happy little spot of not having a whole lot of users compared to the other big frameworks out there, but Werkzeug and Flask have been successful enough that I can somewhat take part in discussions about web development in the Python world without feeling misplaced.

Pylons and BFG have recently merged into a new framework called Pyramid and this was one of the greatest moves in Python's web framework history. TurboGear's fate is not yet known, but it's not too unlikely that it will be based on Pyramid. Not because it's good to have less frameworks by definition, but because they were similar in scope and aiming for the same just in slightly different ways. It's probably comparable to the Ruby on Rails and Merb merge just on a slightly smaller scale.

I personally would love to see a merge of Bottle and Flask for instance because both are aiming for the same thing as well, but unfortunately that seems to be pretty unlikely due to the fact that Bottle does not want to have any dependencies. However switching from Bottle to Flask would be a piece of cake for any Bottle user as that process could be fully automated. Lately Flask also comes in a “Kitchensink” release that is a zip file with Flask and all dependencies to drop into a folder. That way you don't have to deal with virtualenv or anything else if you don't want to or if you can't.

Another possible merge would of course be Werkzeug and WebOb. With better communication early on this problem would have never been and we would only have one library now. Independent of if such a merge will be possible or not, Werkzeug is currently in the process of being cleaned up and improved so that a switch to WebOb or from WebOb could be possible. I don't have any direct plans yet but I don't see a reason why that shouldn't eventually happen. There is one big philosophical difference between WebOb and Werkzeug which is how much of data manipulation should go back into the WSGI environment, but nothing that couldn't be solved so that everybody would be happy. Both WebOb and Werkzeug are in the progress of becoming more like each other already and there is clearly place for going further. Python packaging is improving alongside which makes depending on one library more not a big problem these days, so that shouldn't be the problem either in case a merged library might not have all the features Werkzeug or WebOb previously had.

What makes me incredible happy currently is that the developers of most Python frameworks or WSGI implementations have contact with each other in some form or another and there is potential for working together. This is especially interesting because upcoming and smaller projects like Flask can learn a lot from existing solutions and try to learn from their mistakes because they still have the possibility. Django has to care a lot about their existing users and can't make more courageous steps whereas this is possible for Flask and Pyramid for instance.

Working Together

This goes hand in hand with what I wrote above. Even if there is more than one library for the same use case, there is no reason why people should not work together. For instance it is in the interest of every user that when one framework had a security problem other developers get some insight in what the problem and solution was as the chances are high that a similar problem might exist in another framework as well. Also it's in the interest of everybody involved that Python stays an interesting platform for web developers so a consensus on various things (WSGI, packaging standards, database APIs etc.) is important.

With that I want to primarily encourage developer to take place in such discussions who are currently not doing that. Most frameworks have IRC channels on Freenode and there are also various backrooms where such discussions can take place.

This entry was tagged python, thoughts and wsgi