PyContracts is one such library, stable enough to merit a version number larger than 1.0. I uploaded it on the PyPI software repository, so that anybody can install it using:

easy_install PyContracts

(or: pip install PyContracts)

PyContracts can be used to declare constraints on the arguments and return value of the functions. While it can be used for type-checking, I found it much more valuable for expressing complicated constraints on the values rather than on the types. For example:

@contract(color='seq[3](>=0,<=1)')
def paint(color):
    ...

This checks that color is a sequence of 3 elements, and each element is a number between 0 and 1. Any sequence is allowed: lists, tuples, Numpy arrays, etc.

Note that it would be very tedious to do by hand:

def paint(color):
    if ( not isinstance(color, Sequence)
         or len(color) != 3):
        raise ValueError('I need a sequence of length 3.')
    for c in color:
        if (not isinstance(c, (int, float))
           or c<0 or c>1):
            raise ValueError('Colors must be in [0,1]')
    ...

All these tests are done automatically by PyContracts, and similar error messages are given.

Here’s a more complicated example. Suppose you want to write a function blend() that takes a list of RGB or RGBA images, blends them together, and return the blended images.

There are several checks you need to do: the input is a list, there are at least two images, each image is RGB/RGBA, each image is the same size, and so on.

With PyContracts you can express all of that very compactly:

@contract(images="list[>=2]( array[HxWx(3|4)](uint8) )",
         returns="array[HxWx3](uint8)")
def blend(images):
    ''' Blends a series of images together. '''
    ...

See the PyContracts home page for more information.

I added duplicity to my Time Machine setup for day-to-day backups. I also found a way to backup my GMail account using getmail. Getmail is written in Python, so I looked a little bit into the libraries that can be used to interact with IMAP. It’s actually very easy to retrieve messages or other statistics; so I had to do something with it.

You’re asking why? Why? Because I love data! I love data like Tarantino likes making movies.

I wrote a script that periodically logs the headers of flagged messages in my inbox, and another that reads the logged data, and plots a couple of statistics: stress, defined as the number of flagged messages; and procrastination, defined as the median age of those messages.

Here’s a snapshot of the result:

For now, I only have three days of data, but you can see it live on my webpage and track my stats in the future.

This is especially useful if you’re waiting for an answer from me!

I got a new Macbook pro and spent a considerable amount of time reinstalling my development and research environment. In the hope of saving some time during the next reinstall, I documented everything I installed. I thought I’d write a blog post about it, thinking that this list might be useful to someone else.

Developing environment

• First thing first: the developer tools from Apple; they come in the install CD.
• macports is my choice to complete the Unix environment. Packages installed: wget, ffmpeg, mplayer, imagemagick, autossh, aspell.
• python is my current language of choice. The indispensable packages to learn and use are numpy, scipy, matplotlib, pytables, opencv. The Enthought Python Distribution is the most convenient package, although I have been having a few small problems with the 64 bit version.
• Eclipse is my favorite multilingual IDE, of course with pydev, the Python plugin.
• textmate is the best casual editor you can find for OS X. The essential plugins are the matlab bundle, and the remate plugin, to work over sftp links.
• The inconsolata fonts are my favorite programming fonts. On Mac there is already Consolas, but Inconsolata is a free equivalent that you can install on Linux as well.
• cmake is the best solution for building and packaging C/C++ projects.
• After years with subversion, I am now a git convert. I found the best solution for Mac is to just install the binaries from the official website.
• hdfview is a nice HDF viewer. See a few reasons why you should use HDF.
• I dumped Parallels for VirtualBox: it’s free, and better.
• You should drop bash for zsh. The best theme/plugin manager for zsh is oh-my-sh.

Networking

• Chicken of the VNC is still the best VNC client around. In theory all VNC clients should be compatible with all servers; in practice, there are all sorts of incompatibilities, and Chicken of the VNC seems to play along well, especially with older Linux servers.
• With synergy and a couple of computers, you can create a fancy Matrix-style C&C environment.
• JungleDisk is my current favorite solution for automatic offsite backup (coupled with Time Machine for onsite backup).
• expandrive is a must if you are working with multiple machines.
• I switched from Firefox to Chrome; it’s faster, and has better memory handling. The indispensable plugin is adblockplus.
• autossh might be useful if you need to establish SSH tunnels towards your machines (example: to secure VNC).

Doing research

• Evernote saved my sanity! It is my solution for all the random bits of information (everything that I care about, but not so “stable” as to require a repository.)
• Papers is the other piece of software that saved my sanity. Highly recommended.
• Jabref is better than Papers at handling .bib references; useful at writing time when you want to have more control on formatting.
• Skim is better than Preview for reading long PDF files.
• Keynote has been a welcome liberation from Powerpoint. There was a period in which I used to do presentations with LaTeX using PowerDot, but nowadays I do everything with Keynote.
• The best LaTeX distribution for Mac is MacTex.
• If you are writing raw LaTeX, you are probably wasting your time; LyX gives you a nice GUI environment, and you still can have the flexibility of LaTeX when you need it.
• Staying up late in front of your screen screws up your melatonin production. Use flux to minimize this problem.
• Use Freedom to cut your internet connection when you really have to work. (Unfortunately it is not free anymore.)
• Use RescueTime to assess your productivity (warning: it can be very demoralizing!)
• SimplyNoise is useful when your work environment gets too noisy.
• Piping to mplayer/mencoder, with perhaps a second pass with ffmpeg, is the best solution to create high-quality videos for your research.
• VLC plays everything.
• Sometimes I forget huge log files in some remote directory. I solved this problem using GrandPerspective.

Software that I have to install but I get no joy in using

• Adobe Acrobat is the bloatest piece of software I have ever seen. I hate its intrusive “update manager”. But it is sometimes useful for checking which fonts a PDF is using.
• Matlab is something I sweared to use again only when forced.
• Mathematica is still enigmatic and profoundly non intuitive for me.
• There’s no alternative to Skype.

Miscellaneous

• FunctionFlip for turning off F9/F7. Useful if you have big and imprecise fingers that always press F9 (forward song) while going for F10 (mute).
• Music Brainz Picard is the best tagger/organizer for MP3 files. MP3 tagging is my favorite procrastination activity.
• gmail notifier
• OGG drivers for QuickTime
• geektool has some interesting uses (example).

def compute_derivative(x, dt):
  deriv_filter = numpy.array([-0.5, 0, 0.5]) / dt
  d = scipy.signal.convolve(x, deriv_filter, mode=1)
  d[0] = d[1]
  d[-1] = d[-2]
  return d

Hint: this snipped is correct:

def second_derivative(x, dt):
  return compute_derivative(compute_derivative(x, dt), dt)

Moral of the story: always, always, always write unit tests, otherwise you run the risk of spending nights trying to understand why certain flies go left when they are supposed to go right, and in the end, who knows, they might prefer to go left, this is not an exact science, maybe this is an important discovery, perhaps I need more coffee.

Given Abbeel’s research curriculum, I jumped to reading the preprint to see if there was some learning involved. Unfortunately, it seems that the techniques used are
fairly standard (precise state estimation + giant state graph + motion planning). Still, it is a very impressive application.

The contribution highlighted by the paper is the detection of appropriate folding points. While the robot is holding and slowly rotating the cloth, several cameras observe the scene and can reconstruct a 3D model. The analysis of the 3D model allows to detect the towel’s borders, which are the appropriate folding points.

The paper certainly shows that Willow Garage’s robots, and accompanying software, are a robust platform for developing complex applications. For example, this application involves interplay between robot locomotion, stereo vision, and motion planning. The robot must move its arms to grab the towel at the desired folding point, but, at the same time, it must not impact it in other parts. This implies that the (a priori unknown) shape of the towel must be included in the motion planner’s world representation.

All in all, it’s one step towards the robotic maid!

(read Part 1, Part 2, Part 3)

I went to the Great wall and the Ming tombs with an “official” organized tour. Apparently, if you choose a cheaper options, the driver will stop in a closer but not as beautiful section of the wall.

The Ming tombs are a couple of big halls in front of the actual tombs, which are under a hill and still have to be excavated.

“Mao stopped here to take a rest” — I’m sure it wasn’t this cold, it’s freezing!

After the tombs, they take us to the government Jade shop, which is the only place in China where haggling is forbidden.

At the great wall, we climb using single-seat train cars:

The wall follows precisely the set of points with singular Hessian:

On the way down, it’s a roller-coaster!

After Shangai, the next destination for Teja and I, and Lina as our teacher and guide, is Hangzhou (“heaven on earth” according to a Chinese saying). Plan A is to take the train: the station has just been built and looks like an airport.

Unfortunately there aren’t any tickets left for the night. We propose to try to buy a ticket from the people waiting, but apparently that is illegal. In the end, we end up getting on a black taxy, a private car (I’d never do that in the US!). This guy accepts to take us to Hangzhou for 100 RMB ($15), which is more or less the price of the regular bus ticket. We hop into this car that looks older than disco music. We instinctively look for seatbelts, but there aren’t any. Anyway, we relax a bit after the prospect of sleeping in the train station for catching an early morning train.

A few minutes later, we arrive at the toll station and we park on the road shoulder. There’s another group of men and cars, and it seems that our driver wants to offload us to another car. He seems not to have an agreement with these people, so he walks in the middle of the traffic stream and starts stopping cars, to see who can give us a lift. An SUV accepts. So he make us run in the middle of the freeway to get to this other car. When we get there, we find ourselves in this car with other 7-8 people. They want all the money now, but Teja and I don’t want to pay until we’re at our destination. They start arguing and yelling at Lina, who’s though, so she yells back. The situation is tense and we decide to give them all the money.

In the end, we make it to Hangzhou, which is even colder than Shanghai!

The next day, in the silk market:

We ask a group of Taiwanese people to help us choosing some silk, and they take us to this shop they know:

They also bargain for us. In the end, we pay about 60% of the sticker price:

The main attraction of Hanzhou is the lake and its artificial island. It’s cold!

Teja getting scammed (even though we didn’t really understand what the scam was):

Teja finds a new friend:

Teja fails at ordering food:

People dancing (or exercising?) in the streets at night:

Buying tea with Lina:

The first day of conference. Knock knock! Who’s there? Knock! Who’s there?

Elisa in pre-presentation worrying mode, and me distracting her:

Old town Shanghai:

Andy is a ninja:

Dr. Wierman explains the Baltimore way to eating a crab:

Shuo shows off his mastery of the art of chopsticks by picking up a cube of tofu:

How not to do a presentation:

Children getting ready for the banquet show:

Blade Runner atmosphere:

Best trick ever!

The optimism of Teja:

Me, a dragon, and a tall skycraper:

Around the shops of Shanghai:

Chinese gardens don’t have grass, but lots of bridges, temples, and archs:

Three wise men:

Our new paper in the works: “Inferring leader-follower graph layout from observation of dynamic behavior”

Everybody needs Mao, Saddam, and Osama on their fridge:

Climbing the tower:

The view from the top:

Walking on the void:

On to Part 2.

Graduate students regulate their circadian clock, blood sugar level, and mating periods according to conferences deadlines. For robotics people, the revered date is not September 21 (solstice), but September 15, the deadline for ICRA. For control people, the date is September 15… or 22… or 29, the ever-slipping deadline for ACC.

The peaks of my productivity for the summer were:

• Getting a driving license. It took 2 tries and too much good money spent on driving lessons.
• Understanding what’s the use of all the buttons on my camera, including the elusive “AEL”.
• Finishing reading the last two books of the Hyperion Cantos. (I’m actually disappointed because Simmons doesn’t explain the origin of the Shrike.)

My good propositions for the next academic year are the same as ever:

• I will buy a car,
• I will read all the papers in my giant “INBOX” folder,
• I will go swimming every other day,
• I will take at least two classes,
• I will write more often on this blog,

and on, and on, and on: I consider myself lucky to be in harmony with my procrastination.