Creating my own Point of Sale system, Part 1: Design

This took some time, I'm (mostly) back on track. When I chatted with my SI friends, the first thing I noticed was they asked a fuckton of questions. They grilled me about specifications, use cases, reliability or scalability. They also gave insane price quotes but I'll skip over that. The reason is simple: Specifications save time. I am definitely not used to that. I'm used to quickly hacking together a sqlite database for a chatbot in python and iterating bugfixes/feature additions as I go. So I thought, "Why not do it properly for once?"

Well, that was also a mistake.

The first thing one notices when starting a programming project is the sheer number of decisions. From the programming language to data types, databases and used design patterns, each choice has several impacts and you don't even know the right use case if you don't work with them for some time.

So let's start with the language. I am quite fluent with Python (as in, I can solve most gi…

Creating my own Point of Sale system, Part 0: Start

I had several topics I wanted to write about (both from my dabblings in machine learning and travel stories), but a more urgent thing came up. With a change in Czech legislature, all shopkeepers are now required to authorize all transactions at the Ministry of Finances' servers. They call it EET - Elektronicka Evidence Trzeb. (electronic records of sales) Sadly, POS just reminds me of part-of-speech tags. To deal with the ambiguity, I'll just refer to it as EET system, even though it contains more.

So what exactly is EET?

From march on, every time we make a sale, we have to contact their servers and send them the amount with our hashed ID we got from them by registering. Afterwards, they send an unique receipt ID back, which we have to print and give to the customer. The customer can then at any point check the receipt on their website. The specifications are all published and the state doesn't require any license to use it.
It's rather annoying and requires certain in…

Asian Squad

One of the things I always had problems with was getting along with fellow Vietnamese. At some point I actually hated them. It's hard to name the main reason, so I'll try to talk around it instead. We start with the context. Many Vietnamese (at least the ones I know) came to the Czech Republic from Russia after the split of Czechoslovakia, because it was relatively easy to slip though the borders. They mostly had a similar background - not particularly educated, but with a ruthless (they are fucking brutal  and will stop at nothing to succeed) business sense and a desire for financial security. The main income was selling fake  brand clothes at the market, smuggling other Vietnamese and tax evasion. My parents sold vegetables and fruit, which was at the time kinda good (after 10 years, we had our own flat, even though we came with 1000$), but could not compare to clothes. As a comparison, there was a family who lives next to us that arrived at the same time with the same amoun…

Erasmus fin

I'm sitting on the bus to Prague right now, it will take about 14 hours. The last week has been incredibly hectic, because I moved out of my dorm room to save money and stayed at friends' places. I had to juggle 2 exams with cancelling my bank account/phone number and deregistering at the city council. It was incredibly stressful and I was frankly rather miserable doing all those things at the same time. But from friday to saturday I was completely free. I said goodbye to a couple people (Czechs, Americans,  Computational Linguists, even 2 erasmus friends showed up) and drank beer at the Saar.

It's hard to summarize my  Erasmus year.  It was  an unforgettable experience  which taught me  a great deal.  I probably  did not improve academically (some  courses were pure garbage and in fact I feel I lost my edge here),  but  I learned a lot about dealing with people and making the right friends to get free KFC at 1 am. I also got to know a lot about myself (things you don'…


After playing Tutor for 2 months I became what I at first refused to do because it seemed like a lot of stress for a meager 20 euros more. And guess what. It was. I was quite comfortable with my job (because I was also really successful with both making the Heimbar profitable and doing the dorm events), but the Russian candidate looked really incompetent to me. As in, absolutely useless. I
spent a month convincing the previous president to keep his job, but he refused. I found rather ironic that he did it after voting to reduce the tutors and presidents wages. Thank you prick.

The actual election was boring. I had a talk with the Russian (He tried to convince me that he wanted to help the dorm) and we split the positions. I would play president and he would be the Tutor. Since there were no other candidates, I won be default. On the other hand, the fight for the 3 floor manager positions was rather wild. Not surprising, since we did end their heimbar requirement (and started to pay fo…


It seems I'll be switching to English. I originally wanted to write in Czech to preserve the last bits of my writing style I started losing ever since enrolling in university. I believe my 2 readers won't mind the change. I have been rather busy in the second semester of my Erasmus stay,  but I do intend to fill the gaps. Now is also the perfect time to do so, because it's the exam period.

So let's start with what happened after  coming back to Saarbrücken, flunking ML and then becoming Tutor.

One of the few duties of the floor managers is to make a so called flurfest once per semester. It's a party for the residents, where we collect 7.5 euros from everyone and then use part of it to pay for washing machine maintenance and spend the rest on food and drinks. As the tutor, I was supposed to help with the organization. I was very excited to organize, as it was a new experience for me, but none of the 4 floor managers shared my conviction. I first chose a date  (21st …

Rapid deployment model

Jak jsem se naučil (poživatelné) skořicové šneky za 72 hodin. Na Saarlandské univerzitě máme každou středu prezentaci nějaké země. Většinu práce (kontaktování ambasády pro promo materiály)  odvede centrum pro mezinárodní studenty.  Naše role  vetšinou spočívá v tom tam stát a blbě se usmívat.  K tomu dělá mensa jedno typické jídlo, ale to je slušně řečeno odporné.

Minulý semestr jsem prezentoval Vietnam s dvěma holkama. V mense dávali smažené rýžové nudle ale když jsem přišel, tak měli rýži.

Zeptali se nás, jestli nemůžeme přinést nějaké drobné jídlo, což jsem tehdá absolutně netušil.

Tenhle semestr jsem se ale rozhodl něco udělat. Matfyzák mi dal pár nápadů. Jeden z nich byl kynuté těsto, které jsem nikdy nedělal. Máma jednou dělala plněné knedlíky, ale jinak to byla naprostá enigma. Tak jsem si řekl proč ne. Bohužel je u mě většinou první pokus naprosté fiasko, potřebuju průměrně tak 3 iterace. Dost jsem to odkládal a najednou byla neděle. Ve středu byla prezentace.


Musel jsem…