EuroPython 2014 wrap-up

29.07.2014 14:08

I spent the last week at the EuroPython conference. Since my last visit three years ago, the largest European meeting of the Python community moved from Florence in Italy to the familiar Berlin's Congress Center in Alexanderplatz. Last 7 days were chock-full of talks about everything related to Python, friendly conversations with fellow developers and hacking on this and that odd part of the free software ecosystem. So much so actually that it was a welcome change to spend a day outside, winding down in one of Berlin's numerous parks.

It was an odd feeling to be back in the BCC. So far I knew it only by the Chaos Communication Congresses it hosted before they moved back to Hamburg. I was half-expecting to see the signature Fairy dust rocket and black Datenpirat flags flying in the front. Instead, part of the front yard was converted to a pleasant outdoor lounge area with an ice cream stand while a bunch of sponsor booths took place of the hackcenter.

Traces of the German hacker scene and the community around the CCC could still be easily seen though. The ubiquitous Club Mate was served on each floor. Blinking All Colors Are Beautiful and Mate Light installations were placed on two floors of the conference center. A few speakers reminisced about the congresses and the CCC Video Operations Center took care of the video recordings with the efficiency we are used to from the Congresses. You could even hear a public request to use more bandwidth now and then.

There were several talks with a surprisingly political topic for a conference centered around a programming language. I felt odd listening to the opening keynote from Constanze Kurz about one year of Snowden revelations and the involvement of big Internet companies while those same companies were hunting for new employees just outside the lecture hall. Still, I don't think it hurts to remind people that even purely technical work can have consequences in the society.

From the keynotes, it's also worth mentioning Emily Bache and her views on test driven development and the history and future of NumPy development by Travis Oliphant.

Even though I'm not doing as much Python development as I used to in my previous job, there were still plenty of interesting presentations. In the context of scientific computing in Python, I found the talks about the GR plotting framework, simulations with SimPy and probabilistic programming most interesting. Some interesting scientific projects relevant to my work were presented in the poster session as well, although I had problems later finding them on the web to learn more about them. Especially, the work on propagating measurement errors in numerical calculations done by Robert Froeschl at CERN caught my eye.

I also attended the matplotlib training, although I was a bit disappointed with it. I was hoping to learn more about advanced usage of this Python library I use daily in my work. I enjoyed the historical examples of data visualization and general advice on how to present graphs in a readable way. However most of the technical details behind plotting and data manipulation weren't new to me and we ran out of time before digging into more advanced topics. I guess it was my fault though, since I now see that the training has a novice tag.

Going away from the topics strictly connected to my work, the talks about automated testing with a simple robot and using Kinect in Python left me with several crazy ideas for potential future projects.

During the weekend I joined the Open Contracting coding sprint. Jure and I represented our small Open Data group in helping to develop tools for governments to publish information about public tenders and contracts in a standard format. My result from these two days is the jsonmerge library, which deserves a blog post of its own.

In conclusion, I enjoyed EuroPython 2014 immensely. In contrast for instance with 30C3 last year, it was again one of the those events where I got to talk with an unusually large number of people during coffee breaks and social events.

On the other hand, attending it made me realize how much my interests changed after I left Zemanta. I visited Florence during my last days at that job and I was intimately familiar in all nuances of the Python interpreter. There I joined the spring hacking on the CPython distribution. This year however I was more interested in what Python can offer to me as a tool and not that much in developing Python itself.

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Down time

21.07.2014 21:14

You might have noticed that for the past two days or so this website was off-line. The reason for it is a bit curious.

On Friday, 18 July at 17:45, two of my Ethernet switches failed - one in Logatec and one in Ljubljana, separated by around 35 km. They crashed simultaneously at the exactly the same second.

Here are the relevant log entries of two machines connected to them. Both had clocks synchronized via NTP, so the time stamps should be fairly accurate. The machines logged these messages when their Ethernet adapters reported the loss of carrier signal on the cable from their respective switches:

Jul 18 17:45:21 gildedale kernel: [1658547.286187] PHY: sunxi_gmac-0:00 - Link is Down
Jul 18 17:45:21 chandra kernel: [512418.004319] e100 0000:00:0c.0: eth3: NIC Link is Down


These two pieces of equipment were geographically separated and had nothing in common. As far fetched as it seems that they would fail because of a common reason, this appears to be the case here.

Newspapers reported on Friday afternoon that a small explosion occurred at a transformer station in Ljubljana. The distribution company confirms the event, but doesn't share many details. There is also no official source of the exact time, but the first tweet about it appeared at 17:45.

I guess that whatever occurred at the transformer station caused a transient on the power grid that crashed my switches. It must have been fairly short because two other computers that were connected to the same outlet did not reboot or report any problems.

It's curious that this effect threw both of the switches in a state where they didn't reboot, but didn't function either. One of these is a fairly old, low-cost affair that I have seen behave in this way a few times before. The other one is integrated into a Linksys WRT54GL access point that has been fairly reliable so far.

This is the second time this year that something completely unexpected happened with my servers. It's not that I try to run some kind of high-reliability shop, but it is annoying and makes me appreciate the work real system administrators do each day. I guess that's the cost of trying to stay away from the cloud these days.

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Kickstarting failure

16.07.2014 17:37

Yesterday I stumbled upon the list of supposedly life-changing Kickstarter projects that hovered briefly on the front page of Hacker News. While I receive a regular stream of links to more or less feasible crowd-funding projects through various channels of modern communication, this list caught my eye as being particularly full of far fetched, if not down-right fraudulent proposals.

After skimming through a campaign for electric vehicles, written by someone who doesn't know the difference between energy and power, I stopped for a moment on Shawn West's 30-second rechargeable battery. He is asking for \$10.000 to build a replacement for ordinary rechargeable batteries using a super capacitor for energy storage instead of an electrochemical cell.

Image by Shawn West

Let's consider for a moment his claims: he says that his patent-pending battery using a lithium-ion super capacitor is roughly equivalent to a typical rechargeable battery. He shows us an AA-sized prototype that supposedly contains two integrated circuits: a voltage regulator and a protective circuit that prevents the capacitor from being over- or under-charged. In the FAQ he mentions that the capacity of his battery is 1150 mAh.

Unsurprisingly, on all of his pictures the capacitor is placed in such a way that the model or capacity rating isn't visible. However, with some image enhancement, it's just possible to read out "YUDEN" on one of the photographs.

Taiyo Yuden is in fact a manufacturer of lithium-ion capacitors. Looking through their super capacitor range, there is actually just one model that would fit within the 14 x 50 mm AA sized battery: the 40 farad, 12 x 35 mm cylinder-type LIC1235R3R8406.

Here are its specifications:

C_{cap} = 40 \mathrm{F}
U_{max} = 3.8 \mathrm{V}
U_{min} = 2.2 \mathrm{V}

Let's do some back-of-the envelope calculations: That tiny chip on the circuit board looks like a low-drop linear regulator. In that case, the capacity of the battery given in milliampere-hours is equal to the change in electric charge between the fully charged and fully discharged capacitor (ignoring quiescent current of the regulator):

C_{bat} = \Delta Q = Q_{max} - Q_{min} = C_{cap} \cdot (U_{max} - U_{min})
C_{bat} = 17.8 \mathrm{mAh}

That's barely 1.5% of the claimed capacity!

If we consider for a moment that his circuit actually contains a switching regulator, the situation improves, but only slightly. Given 100% conversion efficiency, the energy that can be extracted from the battery is now equal to the change in electric field energy between the fully charged and fully discharged capacitor:

\Delta W = \frac{C_{cap}}{2}\left(U_{max}^2 - U_{min}^2\right)
\Delta W = 192 \mathrm{J}

Since the inventor claims that his battery does not have a discharge curve, but puts out a steady Ubat = 1.5 V, we can simply convert the energy rating to capacity:

C_{bat} = \frac{\Delta W}{U_{bat}}
C_{bat} = 35.6 \mathrm{mAh}

Obviously, this is much better than the dissipative case above, but the figure is still more than one order of magnitude off from the Kickstarter campaign claim of 1150 mAh. Even giving the author the benefit of doubt and using the largest capacitor from Taiyo Yuden's super capacitor range, the achievable capacity remains much smaller than your vanilla pink-bunny-never-stops alkaline.

Super capacitors are a fascinating component and they certainly have their uses. I kind of like the idea of packaging one into a alkaline battery casing, especially the exposed ring that is used to by-pass the regulator for fast charging. However the claims that this could be used to power your smart phone are ridiculous.

Crowd-funding seems to fuel a big part of the broader-Internet fascination with hardware start-ups these days. I can't help but think that projects with claims that are not challenged in even one of the overly-enthusiastic let's-disrupt-the-industry comments are doing more harm than good to our field.

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Remembrance

08.07.2014 22:06

Back in my childhood I used to spend a lot of time at my grandparent's cottage. It was a wooden house amid a small orchard, just under the top of a hill outside of Ljubljana. My parents would often drive me there in a red Zastava 101 on weekends and holidays. I played with surplus plumbing parts and old tools that were lying around, slept in the attic and had nightmares from having to go to the outhouse after dark.

The cottage was designed and built by my grandfather as a weekend retreat. He was a mechanical engineer who moved to Ljubljana with my grandmother to one of the first apartment complexes in the city, proudly displaying his professional title above the door bell. He was designing turbines for hydroelectric power plants at the heavy machinery manufacturer Litostroj.

When I wasn't wasting potable water or setting things on fire, one of my favorite ways of spending time there was browsing through a book Elektrotehnika v slikah. I could always find it stashed between two planks above my grandfather's bed. It was bound into a hard crimson cover with gold lettering and even back then already had the smell of an old paperback. The title translates to English as Electrical engineering in pictures and it's actually a Slovenian translation of the German original Elektrotechnik in Bildern by Gustav Büscher.

I don't know how that book got there. I doubt that my grandfather learned anything new from it, considering it was printed in 1968 and he finished his 4-book, 5-inch thick thesis on designing Francis turbines 6 years earlier.

In any case, I loved to turn its pages. I looked at the pictures and read the short paragraphs until I knew most of it by heart. First few chapters at least, where the book explains the basics like current, voltage and resistance with simple water analogies. There, almost each paragraph had an illustration that was just serious enough not to appear overly childish and funny enough to keep it interesting. The book was, after all, targeted at adults.

Later chapters went on to describe electric machinery and vacuum tubes with more elaborate mechanical analogies. Judging by the tear-and-wear of the pages, I skipped most of those parts back then. Equations were definitely beyond me at that point, and I'm not sure I even bothered my parents asking about them.

In the chapter about hydroelectricity, the Završnica power plant is featured on several occasions. Maybe it was there in the original version of the book. Or, more likely, the illustrations were adapted when the book was translated. Regardless, Završnica was the first public power plant in the region, so it definitely deserved the attention. By the time this book was published, it was already more than 50 years old.

For a long time, if someone would ask me, that plant would be the only one I could name. I didn't know where it was, but the name has definitely stuck in my head.

Even a month ago I wouldn't know where to put it exactly on the map. I was therefore a bit surprised when I found out that the plant is now being converted into a museum and that I will see it on my visit of HE Moste.

I now know that the dam on river Završnica is a short hike from the town of Žirovnica and is surrounded by a pleasant recreational park. I learned that the pressure pipeline goes under the town and discharges into river Sava below. And I also learned that the prominent building on the top of the hill you see when driving on the Gorenjska highway is its surge tank. Even though machinery in the old turbine hall is being cut open for display, the surge tank above still serves its original purpose. From up close it is an impressive monument to early 20th century hydro engineering.

A walk through the museum revealed many sights that were familiar to me from the book, like the mechanical frequency meter above. I don't think I ever saw a real one before.

What I also learned on the tour is that HE Moste next door was my grandfather's first big design project at Litostroj.

The original bronze Francis turbines dimensioned by him and cast by Litostroj have long been replaced, damaged by cavitation and sand particles carried from the mountains by river Sava. However one of them is now proudly displayed on a plinth in the park in front of the plant.

After HE Moste, my grandfather went on to design power plants throughout the former Yugoslavia and abroad. His design bureau was involved in projects all over the world. He kept a globe in his office marked with flight paths of his intercontinental flights that circled the Earth.

The visit to HE Moste and HE Završnica last month has been as much a technical interest for me as it was a way to remember my grandfather. Without doubt he helped spark my interest for engineering. Either by letting me browse his books or watch him spend his days drawing carefully calculated lines on translucent paper.

He died in 2011 and was designing turbines in his home office for as long as he could hold a pen against a drafting table. His cottage is gone as well and Elektrotehnika v slikah is now standing on a bookshelf in my living room. It was nice to see in person one of more than a hundred power plants he helped design during his career that are still producing electricity.

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