Posts about programming (old posts, page 34)

2010-10-28 12:45

Reason #219 why you should learn english if you are a programmer

Here's pretty much the only place where you can buy Mark Summerfield's "Python 3" book in Argentina: Cúspide.

It costs $372.50 in pesos which is about $94 in dollars.

Oh, and you have to go to a book store to pick it up, or add shipping.

How much does it cost to buy that book in england and have it shipped to your door? $16. That's a whooping 17% of the local cost.

And no, it won't pay import taxes, because books are exempt.

And did I mention that the english version came out a year earlier?

So, if you don't learn english, you pay almost 6 times for the book, and wait a year.

Any programmer that doesn't know enough english is a third class citizen.

2010-10-06 21:39

Rst2pdf 0.16 is out!

Finally, a new release of rst2pdf!

You can get it at its site:

rst2pdf is a tool to convert restructured text (a light, cool markup language) to PDF using reportlab instead of LaTeX.

It has been used for many things, from books, to magazines, to brochures, to manuals, to websites and has lots of features:

  • Font embedding (TTF or Type1 fonts)
  • Cascading Stylesheets
  • Extremely flexible plugin architecture (you can do things like render the headings from arbitrary SVG files!)
  • Sphinx integration.
  • Configurable page layouts
  • Custom cover pages via templates
  • And much, much more...

The biggest change in 0.16 is surely the improved support for Sphinx 1.0.x so if you are using Sphinx, you really want this version.

Also, it has a ton of bugfixes, and a few minor but useful new features.

Here's the whole changelog if you don't believe me:

  • Fixed Issue 343: Plugged memory leak in the RSON parser.
  • Fix for Issue 287: there is still a corner case if you have two sections with the same title, at the same level, in the same page, in different files where the links will break.
  • Fixed Issue 367: german-localized dates are MM. DD. YYYY so when used in sphinx's template cover they appeared weird, like a list item. Fixed with a minor workaround in the template.
  • Fixed Issue 366: links to "#" make no sense on a PDF file
  • Made definitions from definition lists more stylable.
  • Moved definition lists to SplitTables, so you can have very long definitions.
  • Fixed Issue 318: Implemented Domain specific indexes for Sphinx 1.0.x
  • Fixed Index links when using Sphinx/pdfbuilder.
  • Fixed Issue 360: Set literal.wordWrap to None by default so it doesn't inherit wordWrap CJK when you use the otherwise correct japanese settings. In any case, literal blocks are not supposed to wrap at all.
  • Switched pdfbuilder to use SplitTables by default (it made no sense not to do it)
  • Fixed Issue 365: some TTF fonts don't validate but they work anyway.
  • Set a valid default baseurl for Sphinx (makes it much faster!)
  • New feature: --use-numbered-links to show section numbers in links to sections, like "See section 2.3 Termination"
  • Added stylesheets for landscape paper sizes (i.e:
  • Fixed Issue 364: Some options not respected when passed in per-doc options in sphinx.
  • Fixed Issue 361: multiple linebreaks in line blocks were collapsed.
  • Fixed Issue 363: strange characters in some cases in math directive.
  • Fixed Issue 362: Smarter auto-enclosing of equations in $...$
  • Fixed Issue 358: --real--footnotes defaults to False, but help text indicates default is True
  • Fixed Issue 359: Wrong --fit-background-mode help string
  • Fixed Issue 356: missing cells if a cell spawns rows and columns.
  • Fixed Issue 349: Work correctly with languages that are available in form aa_bb and not aa (example: zh_cn)
  • Fixed Issue 345: give file/line info when there is an error in a raw PDF directive.
  • Fixed Issue 336: JPEG images should work even without PIL (but give a warning because sizes will probably be wrong)
  • Fixed Issue 351: footnote/citation references were generated incorrectly, which caused problems if there was a citation with the same text as a heading.
  • Fixed Issue 353: better handling of graphviz, so that it works without vectorpdf but gives a warning about it.
  • Fixed Issue 354: make todo_node from sphinx customizable.
  • Fixed bug where nested lists broke page layout if the page was small.
  • Smarter --inline-links option
  • New extension: fancytitles, see //
  • New feature: tab-width option in code-block directive (defaults to 8).
  • Fixed Issue 340: endnotes/footnotes were not styled.
  • Fixed Issue 339: class names using _ were not usable.
  • Fixed Issue 335: ugly crash when using images in some specific places (looks like a reportlab bug)
  • Fixed Issue 329: make the figure alignment/class attributes work more like LaTeX than HTML.
  • Fixed Issue 328: list item styles were being ignored.
  • Fixed Issue 186: new --use-floating-images makes images with :align: set work like in HTML, with the next flowable flowing beside it.
  • Fixed Issue 307: header/footer from stylesheet now supports inline rest markup and substitutions defined in the main document.
  • New pdf_toc_depth option for Sphinx/pdfbuilder
  • New pdf_use_toc option for Sphinx/pdfbuilder
  • Fixed Issue 308: compatibility with reportlab from SVN
  • Fixed Issue 323: errors in the config.sample made it work weird.
  • Fixed Issue 322: Image substitutions didn't work in document title.
  • Implemented Issue 321: underline and strikethrough available in stylesheet.
  • Fixed Issue 317: Ugly error message when file does not exist

2010-10-01 15:12

Making your app modular: Yapsy

That a plugin architecture for a complex app is a good idea is one of those things that most people kinda agree on. One thing we don't quite agree is how the heck are we going to make out app modular?

One way to do it (if you are coding python) is using Yapsy.

Yapsy is awesome. Also, yapsy is a bit underdocumented. Let's see if this post fixes that a bit and leaves just the awesome.

Update: I had not seen the new Yapsy docs, released a few days ago. They are much better than what was there before :-)

Here's the general idea behind yapsy:

  • You create a Plugin Manager that can find and load plugins from a list of places (for example, from ["/usr/share/appname/plugins", "~/.appname/plugins"]).

  • A plugin category is a class.

  • There is a mapping between category names and category classes.

  • A plugin is a module and a metadata file. The module defines a class that inherits from a category class, and belongs to that category.

    The metadata file has stuff like the plugin's name, description, URL, version, etc.

One of the great things about Yapsy is that it doesn't specify too much. A plugin will be just a python object, you can put whatever you want there, or you can narrow it down by specifying the category class.

In fact, the way I have been doing the category classes is:

  • Start with an empty class
  • Implement two plugins of that category
  • If there is a chunk that's much alike in both, move it into the category class.

But trust me, this will all be clearer with an example :-)

I will be doing it with a graphical PyQt app, but Yapsy works just as well for headless of CLI apps.

Let's start with a simple app: an HTML editor with a preview widget.


A simple editor with preview

Here's the code for the app, which is really simple (it doesn't save or do anything, really, it's just an example):

from PyQt4 import QtCore, QtGui, QtWebKit
import os, sys

class Main(QtGui.QWidget):
    def __init__(self):
        self.layout = QtGui.QVBoxLayout()
        self.editor = QtGui.QPlainTextEdit()
        self.preview = QtWebKit.QWebView()

    def updatePreview(self):

def main():
    # Again, this is boilerplate, it's going to be the same on
    # almost every app you write
    app = QtGui.QApplication(sys.argv)
    # It's exec_ because exec is a reserved word in Python

if __name__ == "__main__":


From now on listings will not include the main function, because it never changes.

But this application has an obvious limit: you have to type HTML in it. Why not type python code in it and have it convert to HTML for display? Or Wiki markup, or restructured text?

You could, in principle, just implement all those modes, but then you are assuming the responsability of supporting every thing-that-can-be-turned-into-HTML. Your app would be a monolith. That's where yapsy enters the scene.

So, let's create a plugin category, called "Formatter" which takes plain text and returns HTML. Then we add stuff in the UI so the user can choose what formatter he wants, and implement two of those.

Here's our plugin category class:

class Formatter(object):
    """Plugins of this class convert plain text to HTML"""

    name = "No Format"

    def formatText(self, text):
        """Takes plain text, returns HTML"""
        return text

Of course what good is a plugin architecture without any plugins for it? So, let's create two plugins.

First: a plugin that takes python code and returns HTML, thanks to pygments.


from pygments import highlight
from pygments.lexers import PythonLexer
from pygments.formatters import HtmlFormatter

from categories import Formatter

class Pygmentizer(Formatter):
    name = "Python Code"

    def formatText(self, text):
        return highlight(text, PythonLexer(), HtmlFormatter(full=True))

See how it goes into a plugins folder? Later on we will tell yapsy to search there for plugins.

To be recognized as a plugin, it needs a metadata file, too:


Name = Python Code
Module = pygmentize

Author = Roberto Alsina
Version = 0.1
Website = //
Description = Highlights Python Code

And really, that's all there is to making a plugin. Here's another one for comparison, which uses docutils to format reStructured Text:


from categories import Formatter
import docutils.core

class Rest(Formatter):
    name = "Restructured Text"

    def formatText(self, text):
        output = docutils.core.publish_string(
            text, writer_name = 'html'
        return output


Name = Restructured Text
Module = rest

Author = Roberto Alsina
Version = 0.1
Website = //
Description = Formats restructured text

And here they are in action:


reSt mode


Python mode

Of course using categories you can do things like a "Tools" category, where the plugins get added to a Tools menu, too.

And here's the application code:

from categories import Formatter
from yapsy.PluginManager import PluginManager

class Main(QtGui.QWidget):
    def __init__(self):
        self.layout = QtGui.QVBoxLayout()
        self.formattersCombo = QtGui.QComboBox()
        self.editor = QtGui.QPlainTextEdit()
        self.preview = QtWebKit.QWebView()



        # Create plugin manager
        self.manager = PluginManager(categories_filter={ "Formatters": Formatter})

        # Load plugins

        # A do-nothing formatter by default
        self.formatters = {}
        print self.manager.getPluginsOfCategory("Formatters")
        for plugin in self.manager.getPluginsOfCategory("Formatters"):
            print  "XXX"
            # plugin.plugin_object is an instance of the plugin
            self.formatters[] = plugin.plugin_object

    def updatePreview(self):
        # Check what the current formatter is
        name =  unicode(self.formattersCombo.currentText())
        text = unicode(self.editor.toPlainText())
        if name in self.formatters:
            text = self.formatters[name].formatText(text)

In short: this is easy to do, and it leads to fixing your application's internal structure, so it helps you write better code.

Full source code for everything.

2010-09-28 15:55

I would be a sellout, but there's not much demand.

For Sale Portobello Mkt
For Sale Portobello Mkt by Jason Jones, under a CC-by-nc-sa license.

It would be natural to anyone who doesn't know me to believe I live a life of luxury, international travel and exotic pleasures [1] but there is a small thing I am kinda ashamed of:

I hardly ever got paid to code.

Really! Most of the money I live on has absolutely nothing to do with whatever you read about on my blog.

I make my living doing things like installing Asterisk in call centers, or configuring MySQL replication, or configuring VPNs using assorted piece-of-crap routers and by all means if you need that kind of work done, please contact Net Managers we are freaky good at it and charge reasonable rates.

But while I like that kind of thing [2] I like other things better. I like programming much more than I like configuring Asterisk!

Then again, I am not a really great programmer. I am just about an average coder, except that I am faster than most.

And lately, an interesting phenomenon has taken place.

How much money I earned thanks to my first 14 years of open source and free software development? $0 [3]

How much money have I earned in the last year of FLOSS development? $500 (and it is bound to be more than that soon).

To a first-worlder that may seem like peanuts, but down here in the land of cheap beef, that's... about 100 pounds of good meat! Or 10 nice dinners in fine restaurants for me and my wife. [4]

I am wondering, is this part of a trend? Have others been receiving more appreciation in the form of money lately?

In any case, it's a great feeling when a work of love (and trust me, noone does something for 14 years for free if he doesn't love it) is appreciated.

Just in case: this doesn't mean you have to pay me to get a bug fixed, or to get a feature implemented. However, it does mean that if you like or use any of my programs and want me to feel good about the time I spent writing them... well, you can just send me a nice email, I will be just as happy. Really!

[1] I do!
[2] And I do like it! It's like a grownup's version of Lego.
[3] I did get boxed SuSE CD sets for a while but I actually lost money on them since I had to pay taxes.
[4] To all those who have contributed I send my sincerest appreciation, and trust me that all this money has been wisely invested on having fun, cheap chinese gadgetry and chocolate mousse.

2010-09-27 20:10

Virtualenv and friends (video)

I am one of the speakers in the cycle of open python lectures at La Tribu in Buenos Aires, and here is the one where I speak about virtualenv, buildout, nose, hudson and other things.

Long video!

2010-09-25 02:41

Quick hack: rss2epub -- it does what it says.

One of my favourite things about Aranduka as a project is that it's an endless source of small, limited side projects.

For example, Aranduka is now close to being able to sync my book collection to my phone. But... what if what I want to read on the train is not a book but, say, a blog?

Well, blogs provide their content via a feed. And A feed is a collection of HTML pieces glued into a structure plus some data like author and such.

And there's a great module for parsing them, called feedparser. And I have written not one, not two, not three, but four RSS aggregators in the past.

So, how about converting the feed into something my phone can handle? [#] Would it be hard to do?

Well... not really hard. It's mostly a matter of taking a small, sample ePub document (created by Calibre) writing a few templates, feeding it the data from feedparser and zipping it up.

For example, this is this blog, as an ePub and here's FBReader reading it:

Share photos on twitter with Twitpic

As usual, the code is open, and it's here in aranduka's mercurial.

It's not really interesting code, and requires templite feedparser and who knows what else.

The produced ePub doesn't validate, and it probably never will, because it has chunks of the original feed in it, so standard compliance doesn't depend on rss2epub.

Also, you get no images. That would imply parsing and fixing all img elements, I suppose, and I am not going to do it right now.

[#] I first saw this feature in plucker a long time ago, and I know Calibre has it too.

2010-09-23 22:33

eBooks and PyQt: a good match

I have been putting lots of love into Aranduka an eBook manager, (which is looking very good lately, thanks!), and I didn't want it to also be an eBook reader.

But then I thought... how hard can it be to read ePub? Well, it's freaking easy!

Here's a good start at but the short of it is... it's a zip with some XML in it.

One of those XML files tells you where things are, one of them is the TOC, the rest is just a small static collection of HTML/CSS/images.

So, here are the ingredients to roll-your-own ePub reader widget in 150 LOC:

  • Use python's zipfile library to avoid exploding the zip (that's lame)
  • Use Element Tree to parse said XML files.
  • Use PyQt's QtWebKit to display said collection of XML/CSS/Images
  • Use this recipe to make QtWebKit tell you when it wants something from the zipfile.

Plug some things to others, shake vigorously, and you end up with this:

Share photos on twitter with Twitpic

Here's the code (as of today) and the UI file you need.

Missing stuff:

  • It doesn't display the cover.
  • It only shows the top level of the table of contents.
  • I only tested it on two books ;-)
  • It sure can use a lot of refactoring!

Neither should be terribly hard to do.

2010-09-18 01:55

Introducing Aranduka

Yes, it's yet another program I am working on. But hey, the last few I started are actually pretty functional already!

And... I am not doing this one alone, which should make it more fun.

It's an eBook (or just any book?) manager, that helps you keep your PDF/Mobi/FB2/whatever organized, and should eventually sync them to the device you want to use to read them.

What works now? See the video!

In case that makes no sense to you:

  • You can get books from FeedBooks. Those books will get downloaded, added to your database, tagged, the cover fetched, etc. etc.

  • You can import your current folder of books in bulk.

    Aranduka will use google and other sources to try to guess (from the filename) what book that is and fill in the extra data about it.

  • You can "guess" the extra data.

    By marking certain data (say, the title) as reliable, Aranduka will try to find some possible books that match then you can choose if it's right.

    Of course you can also edit that data manually.

And that's about it. Planned features:

  • Way too many to list.

The goals are clear:

  • It should be beautiful (I know it isn't!)
  • It should be powerful (not yet!)
  • It should be better than the "competition"

If those three goals are not achieved, it's failure. It may be a fun failure, but it would still be a failure.

2010-09-14 12:56

Very pythonic progress dialogs.

Sometimes, you see a piece of code and it just feels right. Here's an example I found when doing my "Import Antigravity" session for PyDay Buenos Aires: the progressbar module.

Here's an example that will teach you enough to use progressbar effectively:

progress = ProgressBar()
for i in progress(range(80)):

Yes, that's it, you will get a nice ASCII progress bar that goes across the terminal, supports resizing and moves as you iterate from 0 to 79.

The progressbar module even lets you do fancier things like ETA or fie transfer speeds, all just as nicely.

Isn't that code just right? You want a progress bar for that loop? Wrap it and you have one! And of course since I am a PyQt programmer, how could I make PyQt have something as right as that?

Here'show the output looks like:


You can do this with every toolkit, and you probably should!. It has one extra feature: you can interrupt the iteration. Here's the (short) code:

# -*- coding: utf-8 -*-
import sys, time
from PyQt4 import QtCore, QtGui

def progress(data, *args):
    widget = QtGui.QProgressDialog(*args+(0,it.__length_hint__()))
    for v in it:
        if widget.wasCanceled():
            raise StopIteration

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)

    # Do something slow
    for x in progress(xrange(50),"Show Progress", "Stop the madness!"):

Have fun!

2010-09-10 11:52

The first english Issue of PET (our Python Magazine) is out!

Hell yeah! It has been a lot of work but it's out at

Some articles:

  • PyAr, The History
  • from gc import commonsense - Finish Him!
  • Painless Concurrency: The multiprocessing Module
  • Introduction to Unit Testing with Python
  • Taint Mode in Python
  • Applied Dynamism
  • Decorating code (Part 1)
  • Web2Py for Everybody

It's available in pretty much every format anyone can read, and if your favourite is not there, we will make it for you or may I be smote by the flying spaghetti monster's noodly appendage!

AFAIK there is no other Python magazine being published (feel free to correct me), so it's kind of a big thing for us in PyAr (the Argentina Python community) that we are doing one, and in two languages.

But why stop here? Want it to be available in your language? Contact us at [email protected] it may be doable!

And of course, very soon there will be a call for articles for Issue 2, and trust me: that one's going to be epic: this one was just a warmup.

Contents © 2000-2019 Roberto Alsina