Wednesday, November 24, 2010

Upgrading from buildbot 0.7.12 to 0.8.2

Some notes from my experience upgrading Twisted's buildmaster installation:


  • Jinja2 is at http://jinja.pocoo.org/, not the URL in the BuildBot docs (perhaps fixed by https://github.com/djmitche/buildbot/commit/851b8d74141d2dbf8351e67cf8f3e3c1bb7bbc2e)

  • simplejson was already installed, but BuildBot's "setup.py install" easy_installed another copy of it anyway
  • buildbot.status.html.Waterfall is really gone now

  • The "path_to_root" method of buildbot.status.web.base.HtmlResource is gone, but there is a free function of the same name in that module that does the same thing

  • The HtmlResource method to override to generate content is now "content" not "body" and takes an extra "context" argument (perhaps fixed by https://github.com/buildbot/buildbot/commit/bf9e03061f9c3442b2740addaee464b0dd4b678c)

  • The build history format has been upgraded again, meaning that the master will now spend the majority of its time loading old pickles, upgrading them in memory, using them, then throwing them away so that it has to do the work all over again next time (perhaps fixed by https://github.com/buildbot/buildbot/commit/95f33ad1bd65b5fa06e0fc4614830b1cb04d52db)

  • Some unpredictable quantity of build history from before upgrading will still appear in the web status views, but not all of it

  • public_html/index.html will be moved to templates/root.html by the master upgrader

Saturday, October 23, 2010

tricks for good 2d rendering performance with pygame

pygame's API for initializing a display has a couple attractive sounding flags. Or at least, they sound attractive once you notice that updating your 320x240 window at 30fps is consuming all available cycles on your brand new Intel i9 CPU. They're HWSURFACE and DOUBLEBUF. Hardware surfaces and double buffering is how you make graphics fast, right?



Well... no. You probably can't get a hardware surface anyway, and double buffering is unlikely to help until you figure out how to have a window larger than 320x240 anyway.



What you really need to do to get reasonable rendering performance is make sure that any images you blit to the display have the same color depth. You can do this with the Surface.convert method (you get back a Surface when you load an image from a file, eg a png or a gif). Check the depth of your display surface and then convert your image surfaces to that depth (and just keep the converted versions). Blitting them will get hundreds of times faster.



It's a pretty simple thing, but it's easy to get distracted by HWSURFACE and not notice the depth mismatch (like I did for three days).

Friday, October 22, 2010

pyn is dead, long live pyn

Just about eight years ago I started working on an IRC bot using Twisted, pynfo. I managed to stay interested in working on it for about six months. I kept running an instance of it until this morning. Over the years its features have slowly decayed: it hasn't relayed messages between networks or announced pypi releases for years; more recently changes to Freenode have stopped it from even responding to commands.

As such an old project, I wrote it before I knew about things like unit tests, so even if I were interested in maintaining an IRC bot anymore, it would be easier to start over than try to resuscitate pynfo. Thus, pynfo, I consign you to oblivion. Rest in peace:


USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
exarkun 5621 8.9 12.1 275416 251248 ? Rl 2009 70025:19 /usr/bin/python /usr/bin/twistd -f infobot.tap

Monday, August 2, 2010

June - July Reading List

Wednesday, June 23, 2010

filepath 0.1

Hello all,

I'm happy to announce the initial release of filepath.

filepath is an abstract interface to the filesystem. It provides APIs for path name manipulation and for inspecting and modifying the filesystem (for example, renaming files, reading from them, etc). filepath's APIs are intended to be easier than those of the standard library os.path module to use correctly and safely.

filepath is a re-packaging of the twisted.python.filepath module independent from Twisted (except for the test suite which still depends on Twisted Trial).

The low number of this release reflects the newness of this packaging. The implementation is almost entirely mature and well tested in real-world situations from its time as part of Twisted.

You can find the package on PyPI or Launchpad:

http://pypi.python.org/pypi/filepath/0.1
https://launchpad.net/filepath

Monday, June 21, 2010

python-signalfd 0.1

Hello all,

I'm happy to announce the initial release of python-signalfd. This simple package wraps the sigprocmask(2) and signalfd(2) calls, useful for interacting with POSIX signals in slightly more advanced ways than can be done with the built-in signal module.

You can find the package on PyPI or Launchpad:

http://pypi.python.org/pypi/python-signalfd/0.1
https://launchpad.net/python-signalfd

Friday, June 18, 2010

Asynchronous JSON

Today in #twisted.web the topic of generating large JSON responses in a Twisted Web server came up. The problem was that the data being serialized into JSON was so large that the JSON serialization process itself would block the web server, preventing other requests from being serviced.

The first solution that came up was to split the web server into two pieces, so that the URLs which could have these JSON responses were served by a different process than was serving the rest. This is a pretty decent solution, and it also provides the benefit of using extra CPU cores if there are any available. In this case, it complicated things a little since it meant sharing a session across two processes. So we went looking for another approach.

It turns out that the json module supports incremental serialization. When I saw the JSONEncoder.iterencode method, I thought it would be great used in combination with cooperate to create a producer. This would let an application serialize a large structure to JSON without multiple processes, threads, or unreasonably blocking the reactor.

Here's the little bit of glue necessary to make things work:


from json import JSONEncoder

from twisted.internet.task import cooperate

class AsyncJSON(object):
def __init__(self, value):
self._value = value


def beginProducing(self, consumer):
self._consumer = consumer
self._iterable = JSONEncoder().iterencode(self._value)
self._consumer.registerProducer(self, True)
self._task = cooperate(self._produce())
d = self._task.whenDone()
d.addBoth(self._unregister)
return d


def pauseProducing(self):
self._task.pause()


def resumeProducing(self):
self._task.resume()


def stopProducing(self):
self._task.stop()


def _produce(self):
for chunk in self._iterable:
self._consumer.write(chunk)
yield None


def _unregister(self, passthrough):
self._consumer.unregisterProducer()
return passthrough


By using the iterencode method, this avoids spending too much time generating json output at once. Instead, a little bit of the input will be serialized at a time, and each short resulting string is available from the iterator returned by iterencode.

By using cooperate, the _produce generator will iterated in a way that lets it cooperate with the reactor and other event sources/handlers. A few chunks of json data will be written to the consumer, then execution will switch away to something else, then come back and a few more will be written, and so on.

And by using the producer/consumer interface, if the HTTP client which issued the request doesn't read the results as fast as they're being generated, the server will stop generating new output until the client catches up.

Altogether, this provides a very cool, efficient way to generate JSON output.

Here's an example to make it easier to see how one might use AsyncJSON in a resource:


from twisted.web.resource import Resource
from twisted.web.server import NOT_DONE_YET

class BigIntegerList(Resource):
def render_GET(self, request):
length = int(request.args['length'][0])
d = AsyncJSON(range(length)).beginProducing(request)
d.addCallback(lambda ignored: request.finish())
return NOT_DONE_YET

Wednesday, June 2, 2010

Minuteman Campground Bike Trip

Jericho and I took a quick bike trip out of the city a few weekends ago.

The Minuteman Campground is pretty nice. It's still fairly early in the season, so there were only a few other people there. We brought a tent, but there were also campsites with cabins, which might be nice for longer trips (ie, less baggage).

The ride out was about five hours (including a stop for lunch). Coming back was much quicker, maybe three hours (including a stop for lunch and ice cream).

Overall, a fun trip.

Wednesday, March 3, 2010

Include version information in your Python packages

Quite some time ago, I wrote a list of what to do and what not to do when creating a Python package. In the spirit of that post, I have another do item:

Do include version information somewhere in your package. When I say package here, I'm referring to the Python concept - the thing which can be imported and manipulated programmatically. Here is a random assortment of real-life examples of what I mean:

>>> import sys
>>> sys.version
'2.6.4 (r264:75706, Dec  7 2009, 18:45:15) \n[GCC 4.4.1]'
>>> import OpenSSL
>>> OpenSSL.__version__
'0.10'
>>> import gmpy
>>> gmpy.version()
'1.04'
>>> import gtk
>>> gtk.gtk_version
(2, 18, 3)
>>> gtk.pygtk_version
(2, 16, 0)
>>> import pyasn1
>>> pyasn1.majorVersionId
'1'
>>> import win32api
>>> win32api.GetFileVersionInfo(win32api.__file__, chr(92))['FileVersionLS'] >> 16
212

You can see several conventions represented here. Some of them are better than others (in case you need a hint, gtk is doing something pretty nice; win32api is towards the other end of the spectrum). However, even the worst of these is providing the desired information. Compare this to:

>>> import zope.interface
>>> [x for x in dir(zope.interface) if 'version' in x]
[]
>>> import subunit
>>> [x for x in dir(subunit) if 'version' in x]
[]

This is a simple piece of information, and after you've actually picked a version of something and installed it, it's hardly ever of much interest. However, when it is of interest, you really want to be able to get it. You don't want to rely on the memory of some user about which version they installed when you're tracking down some poor interaction.

So. Do you maintain a Python package? Does it expose its version somehow? If not, fix it!

Saturday, February 13, 2010

Twisted Web in 60 seconds: CGI


Greetings, and welcome back to "Twisted Web in 60 Seconds". In the previous entry, back at the beginning of December, I promised to cover Twisted Web's proxying capabilities. For various reasons I've decided to dump that topic and cover something else instead. So, prepare to learn about Twisted Web's CGI capabilities!




twisted.web.twcgi.CGIScript and twisted.web.twcgi.FilteredScript are the two most interesting classes in this area. They are both Resource subclasses, so many of the features of resources that I've covered so far apply to them. For example, you can use them as the resource in an .rpy script:




from twisted.web.twcgi import CGIScript
resource = CGIScript("/path/to/date-example.sh")




date-example.sh might look like this:




#!/bin/sh

echo "Content-Type: text/plain"
echo
/bin/date




That is, just a regular CGI - nothing special about Twisted Web going on there.




If you need to specify an interpreter for some reason (for example, the CGI itself isn't set executable, or doesn't specify its own interpreter with #! on the first line), you can use FilteredScript instead of CGIScript:




from twisted.web.twcgi import FilteredScript

resource = FilteredScript("/path/to/date-example.sh")
resource.filter = "/bin/sh"




Set up this way, /bin/sh will always be run and passed an argument of /path/to/date-example.sh.

Thursday, January 7, 2010

November - December Reading List


  • SuperFreakonomics. Steven D. Levitt and Stephen J. Dubner.

  • Look to Windward. Iain Banks.

  • PLAN B 4.0. Lester R. Brown.

  • Deathworld. Harry Harrison.

  • Sixty Days and Counting. Kim Stanley Robinson.

  • MetaGame. Sam Landstrom.

  • People of the Book. Geraldine Brooks.

  • The Mystery of Edwin Drood. Charles Dickens.