Today I was asked if I knew how to make a recursively default dictionary (although not in so many words). What that means is that it’s a dictionary (or hash) which is defaulted to an empty version of itself for every item access. That way, you can throw data into a multi-dimensional dictionary without regard for whether keys already exist, like so:

h["a"]["b"]["c"] = 5

Without having to first initialise h[“a”] and h[“a”][“b”].

A dictionary with a default value of an empty hash sprang to mind, but after trying it out I realised that this only works for one level. Recursion was evidently required.

So, here’s the python solution:

from collections import defaultdict
new_dict = lambda: defaultdict(new_dict)
h = defaultdict(new_dict)

And the ruby, which seems overly noisy:

new_hash = lambda { |hash, key| hash[key] = Hash.new &new_hash }
h = Hash.new(&new_hash)

I had to refer to this today, when I discovered (much to my surprise) that git submodules update does, for the most part, nothing.

You might expect it to update all my git submodules to the latest revision. Nope, I’m supposed to cd into each of those directories myself and run git pull myself.

The only hint that git update will do nothing of use is a single sentence in the help page, which mentions as part of the update command’s summary: “This will make the submodules HEAD be detached”. Which is a fairly unintelligible statement, even to someone who’s been using git for about a year now.

I can’t imagine when you would run git submodule update after the initial checkout - why doesn’t git submodule init just do update’s job (actually fetching the initial content), and then maybe we could have an update that actually pulls updates? I’d even be satisfied to have to use a flag, like --hard, --please or --come-on-old-chap-just-do-it-would-you

I’m pretty new to git’s submodules, and so far they just seem to take far too many manual steps (I don’t understand why they’re not fetched by a clone, for starters). I feel wrong saying so, but I miss svn:externals.

Tell me, how are things in the land of the other DVCS’s?

Update: Looks like my git is outdated, the newest version (1.6) allows a --merge or --rebase flag to update which sounds like it does what I want. Now I just need to sort out my mac’s package management :s

(view link)

OSX has this great feature where if you hold down SHIFT at the same time as using your mouse scroll wheel, it’ll scroll horizontally instead of vertically. If you don’t have a laptop, this is an immensely useful trick. Sadly, I couldn’t find any way to get this to happen on linux.

But now, thanks to some direction from stackoverflow, I finally figured out how to do it myself. The world of X11 input hackery is somewhat twisted and full of projects either abandoned or in disrepair, but I finally stumbled across the right set of tools.

If you’d like to get this (rather excellent) feature in linux, you will need the following:

• Install the packages xbindkeys and xautomation: sudo apt-get install xbindkeys xautomation

• Save the following file as ~/.xbindkeysrc.scm :

    ; bind shift + vertical scroll to horizontal scroll events
    (xbindkey '(shift "b:4") "xte 'mouseclick 6'")
    (xbindkey '(shift "b:5") "xte 'mouseclick 7'")
  

• Use your favourite mechanism to ensure that the xbindkeys command is run at the beginning of your xsession (I added it to ubuntu’s “startup items” preference, but you can surely use init.d if you’re comfortable with that).

Today I’ve put up the first “releaseable” version of autonose. Basically, it analyses your code’s imports, and determines exactly which tests rely on which code. So whenever you change a file, it’ll automatically run the tests that depend on the changed file (be it directly or transitively). Give it a go, and please let me know your feedback.

All you need do is:

$ easy_install autonose
$ cd [project_with_some_tests_in_it]
$ autonose

See the github project page for further information (and a screenshot).

Can anyone tell me why ruby’s instance_variable_set would possibly require the name of a variable to start with an “@”, rather than simply assuming it? It’s a ruddy instance variable, after all…

I can find no decent alternative to python’s setattr in ruby, which surprises me.

I was just struck by how lisp-ish javascript is getting (not in the powerful code-as-data way, just the “screw builtin language features, lets just use more brackets for everything” way). Exemplified by this tiny sammy example code:

$.sammy(function() { with(this) {
  get('#/', function() { with(this) {
    $('#main').text('Welcome!');
  }});
}});