Posts in 2020


Fast database UPDATE/DELETE operations

You may be familiar with the use of a database upsert of MERGE operation to insert a record into a table or update an existing record, if that record already exists. This evaluates the condition for finding the record only once, and is therefore more efficient than other alternatives. How can you efficiently handle a reverse operation of updating a record and deleting it if some condition holds?

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Raspberry Pi 400 vs ZX Spectrum

The release of the Raspberry Pi 400 personal computer reminded me of a wildly popular home computer that was launched in a similar computer-in-a-keyboard format almost 40 years ago: the Sinclair Research ZX Spectrum. I decided to compare the two, following the steps of an earlier comparison I performed between the 2015 Rapsberry Pi Zero and the 1957 Elliott 405.

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Error handling under Unix and Windows

One thing that struck me when I first encountered the 4.3BSD Unix system call documentation in the 1980s, was that each call was followed by an exhaustive list of the errors associated with it. Ten years later, when I was going through the Windows API, I was disappointed to see that very few functions documented their error conditions. This is a big deal.

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Shell scripting for software developers

In an open online edX course on Unix tools I was running over the spring with more than a thousand registered learners, I got asked for ideas on how shell scripts can be useful. This is an intriguing question, because the course focuses mainly on performing one-off tasks in the areas of software development, data engineering, and system administration, rather than automation through shell scripts. In response, I posted how shell scripting improves my personal productivity. Here’s my take on how shell scripts are employed in diverse software development tasks. I plan to post further installments on system administration and data analytics.

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IBAN length and DESI score

Looking at the formats of European country international bank account number (IBAN) codes, I noticed that the IBAN length didn’t seem to be significantly correlated to the country’s population. Could it be related to the country’s IT maturity? I tested that using as a proxy the EU Digital Economy and Society Index, and the results were stunning.

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Auto-correct text entered with the wrong keyboard layout

To enter text in some languages you press a special key combination (e.g. Alt-Shift) to toggle the keyboard layout. The keyboard layout context is typically kept separately for each window. This is generally good, but forces you to remember (or check) the current layout every time you switch to another window. If you forget to do that, the text you type will come out as gibberish. To me this happens often enough that I automated the fixing of such text.

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The titanic battle between big iron and microprocessors

I’m a child of a microprocessor age. I learned to program on computers powered by a variety of microprocessors starting with the 4-bit SC43177/SC43178 pair powering a Sharp PC-1211, continuing with the 8-bit Zilog Z80 on the TRS-80, the Zenith Z-89, and the Sinclair ZX81 computers, and graduating to 16-bit processors: the Texas Instruments TMS9900 powering its manufacturer’s TI-99/4A home computer and finally Intel’s 8088 on an IBM Portable (16kg) Personal Computer. At the university I encountered an IBM System/370 4331/2 mainframe, which I regarded with outer contempt. It seemed to me like a dinosaur: slow and unwieldy, lacking interactivity, color, and graphics. I couldn’t fathom why businesses were using such monsters. I now understand that I was watching an amazing race between the sprightly but woefully simplistic microprocessors and the powerful but slow-moving mainframes.

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Contact tracing with a Raspberry Pi Zero-W

Contact tracing via smartphone apps has been widely touted as an important way to control and limit the spread of the COVID-19 epidemic. However, basing contact-tracing on phone apps has several limitations. Here are instructions for constructing a contact tracing device prototype with a Raspberry Pi Zero-W. The constructed device is compatible with the Apple/Google Bluetooth contact tracing specification. It runs the Epidose software, which is based on the DP3T “unlinkable” design.

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A chat protocol for remote lectures

Due to the current coronavirus lock-down we’re holding all our lectures remotely; currently via Microsoft Teams meetings. Students can see my presentation and me talking, and I can hear them, when they unmute their microphone. (By default they are muted to avoid noise and echoes.) What I thought I would miss is the lecture’s interactions: the responses I get to questions I pose to the students, as well as students’ comments and questions. We found out that such interactions can work quite well — at times better than in the face-to-face lecture — by following a simple interaction protocol.

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Shell scripting for personal productivity

In an edX course on Unix tools I am running these weeks, I got asked for ideas on how shell scripts can be useful. This is a very interesting question, because the course focuses mainly on performing one-off tasks in the areas of software development, data engineering, and system administration, rather than automation through shell scripts. Here’s how I’m using shell scripting to enhance my personal productivity. I’ll post further installments regarding software development and system administration.

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What explains the counter-intuitive numbering of chip pins?

One of the first things one learns in electronics is how chip pins are numbered. In the common dual in-line package (DIP) pin numbering starts from the left side of a notch appearing on the top of the package and continues counterclockwise until it reaches the other side of the notch. Why are pins counter-intuitively numbered in a rotating fashion rather than by columns as one would expect for a rectangular package? And why is the numbering not following the direction of a clock’s numbers? I think that both decisions can be traced back to history.

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Installing PyTorch on a Raspberry Pi-3B+ redux

This is an update to articles for installing the PyTorch machine learning library on a Raspberry Pi that have been published by Amrit Das in 2018 and Saparna Nair in 2019. It builds on them by updating the required settings and introducing a fix and a few tweaks to make the process run considerably faster. Although there are Python wheels floating around that offer PyTorch as a Raspberry Pi Python package, downloading them from unverified sources is a security risk. Here’s how to install PyTorch from source.

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Seven reasons to add Unix command line expertise to your tool chest

On Tuesday March 17th 2020 my free online massive open online course (MOOC) on the use of Unix command line tools for data, software, and production engineering goes live on the edX platform. Already more than one thousand participants from around the world have registered for it; you should still be able to enroll through this link. In response to the course’s announcement seasoned researchers from around the world have commented that this is an indispensable course and that it is very hard to beat the ROI of acquiring this skillset, both for academia and industry. In an age of shiny IDEs and cool GUI tools, what are the reasons for the enduring utility and popularity of the Unix command line tools? Here’s my take.

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What can software developers learn from the Soviet Moon Landing Program?

In the twentieth century space race between the Soviet Union and the United States the former started way ahead. In 1957 it launched the first artificial satellite, Sputnik 1, and in 1961 it had Yuri Gagarin orbiting the Earth as the first human to space. Yet, when it came to landing a person on the Moon it flopped spectacularly, abandoning its N1 rocket and Soyuz spacecraft program after a series of fiery failures. It turns out that the problems of Soviet program’s N1 rocket — one cased one of the largest artificial non-nuclear explosions in human history — offer some important lessons to software developers.

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Was Knuth Really Framed by Jon Bentley?

Recently, the formal methods specialist Hillel Wayne posted an interesting article discussing whether Donald Knuth was actually framed when Jon Bentley asked him to demonstrate literate programming. (Knuth came up with an 8-page long monolithic listing, whereas in a critique Doug McIlroy provided a six line shell script.) The article makes many interesting and valid points. However, among the raised points one is that the specified problem was ideal for solving with Unix tools, and that a different problem, such as “find the top K pairs of words and print the Levenshtein distance between each pair”, would be much more difficult to solve with Unix commands. As the developer of an edX massive open online course (MOOC) on the use of Unix Tools for data, software and production engineering I decided to put this claim to the test.

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Become a Unix command line wizard
edX MOOC on Unix Tools: Data, Software, and Production Engineering
Debug like a master
Book cover of Effective Debugging
Compute with style
Book cover of The Elements of Computing Style
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