This week, various student organisations protest against major cuts in the funding of education and research.

A reader of dutch, can visit their site.

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# Author: Bas Westerbaan

## Dutch student protest

## Unique followers on Twitter

## Normul

## Cantor never bores (1)

## Bond against Loanwords

## 21

## Windows 7 Sins

## Twitter and Facebook

## PijsMarietje

## Damned DOM (1)

## Unicode to ASCII (1)

## Django annoyances: no reverse

## Javascript’s stupid

## GStreamer: accurate duration

## Spacing up- and downarrow properly for up- and downsets

## Fosdem (3)

## Timestamp 1234567890

## Aperitif for order

## 2009

## On-demand singleton for Python

This week, various student organisations protest against major cuts in the funding of education and research.

A reader of dutch, can visit their site.

As pointed out by Jorg Kennis, Twitter‘s new lists feature make it hard to determine the amount of unique followers. I’ve written a simple script, using a slightly modified TweePy, to determine the amount of unique followers.

Example usage:

`bas@w-nz ~/twitter-unique-followers $ python twitter-unique-followers.py JorgK -ubwesterb`

Password:

rate_limit_status: remaining_hits: 112

Jorg Kennis

followed directly by 182

in lists

RPtje/vriendenbekenden subscribed to by 0

JorgK/TechNL subscribed to by 0

sentfanwyaerda/nijmegen1 subscribed to by 9

JorgK/Friends subscribed to by 0

sjorsjes/Community subscribed to by 0

robinspeijer/iPhone subscribed to by 1

nielsschooneman/iPhone subscribed to by 0

JeanPaulH/iPhoneclub subscribed to by 5

number of unique followers: 198

You can download it here. I could write a simple webpage with the same functionality, if anyone would mind.

Normul normalizes URLs. It expands shortened URLs:

`>>> from normul import normul`

>>> normul('http://bit.ly/1I4VQ')

{'type': 'other', 'normalized': 'http://www.shinguz.ch/MySQL/mysql_mv.html', 'original': 'http://bit.ly/1I4VQ'}

And shows useful links for hosted-images:

>>> normul('http://yfrog.com/6c5krj')

{'image': {'full': 'http://img228.imageshack.us/img228/1079/5kr.jpg', 'thumbnail': 'http://img228.imageshack.us/img228/1079/5kr.th.jpg'}, 'type': 'image', 'original': 'http://yfrog.com/6c5krj', 'normalized': 'http://yfrog.com/6c5krj'}

You can find the simple but convenient sourcecode here.

Given a set of countable sets [tex]K[/tex], such that [tex]K[/tex] is totally ordered by inclusion, videlicet for every [tex]A,B\in K[/tex] either [tex]A\subseteq B[/tex] or [tex]A\supseteq B[/tex]. Intuitively, for at every step in this chain one element at least must be added, one expects the set [tex]K[/tex] to be countable as well.

Suppose [tex]K[/tex] is countable. Then the union, [tex]\bigcup K[/tex] is a countable union of countable sets, hence countable. (Suppose [tex]k: \mathbb N \to K[/tex] is an enumeration of [tex]K[/tex] and [tex]f_i: \mathbb N \to k(i)[/tex] enumerations of the elements of the chain. Then [tex]f_0(0), f_1(0), f_0(1), f_2(0), f_1(1), f_0(2), \ldots[/tex] enumerates [tex]\bigcup K[/tex].)

Thus [tex]\bigcup K[/tex] is an upper bound of [tex]K[/tex]. In the poset of countable subsets of some set [tex]U[/tex], of which [tex]\bigcup K[/tex] is a subset, every non-empty chain has an upper bound. Hence, using Zorn’s lemma there is a maximal element, say [tex]M[/tex].

Suppose [tex]U[/tex] is uncountable, then there exists a [tex]\star \in U \backslash M[/tex]. [tex]M \cup \{\star\}[/tex] is most definitely also countable and [tex]M \subset M \cup \{\star\}[/tex] which contradicts [tex]M[/tex]’s maximality. We are forced to conclude that there exists an uncountable chain of countable sets.

Cantor’s set theory keeps surprising.

Update: an example of such a chain is the set of the countable ordinals.

Another update: a “more concrete” example are the downsets in [tex]\mathbb Q[/tex] without the empty set and [tex]\mathbb Q[/tex] itself. These downsets correspond to real numbers, see Dedekind Cuts.

Although I don’t bear any animosity against most dutch loanwords (except those Anglo-Saxon), the dictionary of the dutch Bond tegen Leenwoorden is a true joy to read.

Since yesterday I, for the first time, enjoy the anything-but-special age of 21 years.

Windows 7 Sins. I strongly agree with points 1, 3, 4, 5 and 6. The arguments for points 2 and 7 are a bit weak, but I do agree with the conclusions.

For the non US audience, it would have been nice to note that if Microsoft (or the US) would recall all foreign licenses for Windows, our entire government is crippled.

were both victim of a DDoS today. Silently, I always hoped that a really long-lasting one will convince them to put effort in a distributed scheme.

Maybe I should be waiting for another Wave.

At the faculty for sciences there are canteens for students. In each of these, there’s sound equipment connected to linux boxes. On each of those linux boxes, we run a music-request-server called *Marietje*. I just finished writing a front-end in Javascript. It wasn’t a pain. As instead, the use of jQuery was a bliss.

The frontend for one of those boxes and the source code (see the `ajax`

folder).

When I wanted to react to any changes to a `input`

textbox immediately, my first instrinct was to use `onChange`

. `onChange`

, however, is called when the `input`

loses focus. `onKeyPress`

then? Isn’t called on backspaces. `onKeyDown`

, maybe? It does get called, but the effect of the keystroke isn’t yet applied, for the return value determines whether it that is done in the first place. (Same story for `onKeyPress`

by the way.) `onKeyUp`

does work a bit, except if someone is holding down a single key, for a while.

The solution: hook `onKeyUp`

and use `setTimeout`

with a timeout of 0. Yugh. I hate DOM.

*Big Fat Disclaimer: I actually tested this only on one browser.*

When I want to generate usernames from real names, which can contain non-ascii characters, you can’t simply ignore the unicode characters. For instance, danielle@blaat.org is the right e-mail address for Daniëlle, danille@blaat.org isn’t.

There’s trick. Unicode has got a single code for ë itself, but it has also got a code which (simplified) adds ¨ on top of the previous character. The unicode standard defines a normal form in which (at least) all such characters, which can be, are represented using such modifiers. If you then simply ignore the non-ascii representable codes, you’ll get the desired result.

In python: `unicodedata.normalize('NFKD', txt).encode('ASCII', 'ignore')`

.

However, this isn’t *the* right solution. For instance, in german, one prefers ue as a replacement of ü over u.

`select_related`

Consider

`for page in Page.objects.all():`

.

print page.title

for comment in page.comments.all():

print comment

There will be a single query to fetch all pages, but there will be for every page another query to fetch its comments. Luckily, Django has got a nice trick up its sleave: `select_related`

. Would I use instead of `Page.objects.all()`

, `Page.objects.select_related('comments').all()`

then Django will use a single joined query to prefetch comments for each page.

However, Django’s `select_related`

only supports forward one-to-many references. No many-to-many; certainly no reverce many-to-many; no reverse one-to-many and no, not even reverse one-to-one (yet). A developer claims it’s impossible (which is bullshit), another asks for patches, which means he doesn’t care doing it himself.

It’s quite easy to manually code around the missing reverse `select_related`

, but it takes too many ugly lines compared to the single word it could’ve been.

`Date`

constructor`new Date(2009, 1, 1)`

represents the first of February 2009. Not the second of February nor the first of January. Why this stupidity?

When decoding, for instance, a variable-bitrate MP3, gstreamer reported durations are, to say the least, estimates. I’ve tried to get a better result in a few ways. First off, some files yield a `duration`

tag, but even if you’re lucky and it is there, there are no guaranties about precision. After that I tried seeking to the end (`GST_SEEK_END`

) of the stream and querying the position, which gstreamer didn’t like. Finally, routing the audio into a `fakesink`

, waiting for the end of stream and then querying for the position gives the right result. It’s not the prettiest method, but it works.

This is a Python script that prints the duration of a media to stdout.

[tex]f(\uparrow x)[/tex] is ugly, but [tex]f(\left\uparrow x\right.)[/tex] is nice! The solution: prefix `\uparrow`

with `\mathopen`

.

In a few hours I’ll travel the short distance to Bruxelles to visit Fosdem. Once again I’m pretty excited :). Lets hope this time the pink elephants of the Delirium Cafe don’t crush me. If you’re also going, drop me a comment.

It’s soon. The 14th of februari, 00:31:30 (Europe/Amsterdam). Will the world end? Will ancient libc code giggle and break?

Assign 1 to True and 0 to False. Now the minimum corresponds to “and” and maximum to “or”. If you give it a bit more though, less or equal to corresponds to implication. This is a lot more general than this specific case. Add .5 for a third value (eg. NULL) and it still yields natural results.

We can recognize the behaviour of minima and maxima in a lot of other things. Take for instance set inclusion as order with intersection as minimum and union as maximum. Actually, the link between general order and set inclusion is frequently made to then propose that “intersection of two set of cases” and “logical and” do look a lot alike.

This is just the tip of the huge iceberg. Order appears everywhere! Everywhere in Math. Everywhere in CS. And its just recognizing simple order I’ve demonstrated. Other useful concepts in order theory that I didn’t even touch are Galois Connections and formal concept analysis.

Oh, another example of an order are integers with bitwise or and bitwise and. It is left as an exercise to the reader when one integer is greater than another.

Interested? Buy an Introduction to Lattices and Order.

Happy Newyear!

Some singletons eat slightly more resources, than you want to give them for free. For instance, if you have a home-brew threadpool singleton, you don’t want it to create its threads if you are not going to use it. The solution: a simple function that creates a stub which proxies attribute access to an ad-hoc created instance.

Usage: `create_ondemand_singleton('mylibrary.Threadpool', MyThreadPoolClass)`

.