Justus Perlwitz

04 May 2018

What Hackathons Teach About Making Products

I like hackathons. Hackathons are competitions that run over multiple days — typically a whole weekend — and in which the participants — programmers and designers — solve a challenges in order to win a prize. Typically, there are a few challenges that are all based around some theme — blockchains, sustainability, democracy, and so on.

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27 Apr 2018

Updating Smart Contracts

As time goes on, smart contract requirements change. Often, a feature is added or a bug is found. But, once a smart contract has been deployed on the blockchain, it can’t be upgraded. The entire value proposition of a blockchain is immutability. Yet, in the real world, contracts change all the time. For example, a labor contract will change when new labor laws are introduced. Similarly, there are many circumstances under which smart contracts change as well, such as

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20 Apr 2018

Smart Contract Ownership

When building your smart contract platform — whether on Ethereum or any other blockchain — at some you’ll be faced with the question of ownership. In this article, I will explain three different types of smart contract ownership and discuss their advantages and disadvantages.

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13 Apr 2018

ERC20 Token Allowances

Have you ever wondered how your users can spend ERC20 platform tokens to buy assets and other tokens from you? Or — in more technical terms — how to make sure a smart contract executes a particular function as soon as it receives tokens? This post is all about using ERC20 approve() and transferFrom() to allow your users to do much more than just keep tokens in a wallet.

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06 Apr 2018

3 Useful Python Code Patterns

Over the years I have found out how important it is to constantly challenge yourself. Coding is craftsmanship. A good craftsman will always try to improve the toolbox they use every day. Code patterns belong in any good toolbox. When used wisely, they allow anyone to clearly communicate their program’s intent to both people and machines. Code is not just something that machines execute — it’s also something that people read, understand, and maintain.

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20 Mar 2018

Anatomy of a Token Platform

I had the tremendous privilege of speaking about creating sustainable token platforms at TokenSky 2018 in Seoul, Korea. Not only did I have a great time presenting some of the ideas that I’ve come across, I also encountered a lot of stimulating questions from individuals and companies all interested in enhancing their platform using some kind of blockchain token.

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09 Mar 2018

Designing a Better Web Analytics Platform

Not many things a business owner has to go through are as scrutinous and unpleasant as a data privacy audit. In the case of Germany, this will include a state commissioner for data protection putting your companies data processing and storage practices under the microscope. Luckily, as it turns out, most of the time you’ll already be doing the right thing. Salting user passwords, allowing customers to delete their account, and allowing users to request all personal data that is being stored about them should be business as usual for most of us.

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02 Mar 2018

The Four Phases of a Data Science Project

Imagine this: You’re pitching an idea for an interesting data science problem that you can solve for your client. The client is sold on the idea and wants to immediately know how fast you can get it done, and more importantly, what the project milestones will look like.

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23 Feb 2018

Memory Usage of Pandas Categoricals

A great method to improve memory usage of Pandas DataFrames is by converting columns with categorical variables to use the data type categorical.

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06 Jan 2018

Effective Data Science Notebooks

I believe that being a data scientist is about communication first, and data science second. This means that two abilities are necessary.

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29 Dec 2017

transform()ing Like a Pro in Pandas

Using .transform(), you can transform the way you aggregate DataFrames.

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26 Dec 2017

Aggregating in Pandas

The other day I caught myself writing one too many df.groupby() in Pandas, and thought to myself:

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23 Dec 2017

Scaling from Pandas to Dask

Scaling Pandas DataFrame aggregations can be quite tricky. I have had a very specific problem to solve that involved aggregates on group by expressions.

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05 Jul 2017

When to use C and when to use Python

I’ve now solved the first 15 Project Euler challenges in C. But then, I’ve hit a road block. Let me explain.

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30 Jun 2017

Sharpening my InfoSec tools

After a long time of being complacent with my skills, I thought I should up my InfoSec game. So far I’ve been mainly busy with figuring out how to enhance application security in my work. That means I learned how to

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27 Jun 2017

The difference between 大切、大事、重要

Let’s look at how 大切、大事、重要 are different.

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15 Jun 2016

A brief UberRUSH overview and tutorial

Uber Rush provides cost-effective on-demand courier services. It is an exciting service that will allow companies to start delivering to local customers faster. Uber tries to make the process as easy as possible by providing an API which can be easily integrated into existing shop solutions and lets customers order cheap and easy shipping. For a high-level overview, please refer to this document.

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04 Jun 2016

Cutting through BS

Being part of the all-singing, all-dancing trap can make us forget our individual selves. A recent conversation with Daniel Hastik in May gave me a few jolts of inspiration to write about something that’s been bugging me.

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25 Apr 2016

How to Replace Judges with Robots

The other day, I found out something real fun: Not all bike lanes in Germany need to be used! Since bike lanes are quite dreadful and not at all safe, I wanted to write a handy tool to show me when to use a bicycle lane and when not. The German traffic code (StVO §2 Abs. 4 Satz 2) dictates:

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06 Dec 2015

The Python 3 Statistics Module and Salaries

Python 3.4 introduced the statistics module. It contains helpful methods for determining basic statistical properties, such as mean, median and standard deviation of samples and populations.

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30 Nov 2015

Byte Histogram in Python 3

I had this curious thought the other day: what is the byte value distribution in binary files, such as an executable? Take for example /bin/echo on OS X 10.11.1.

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22 Nov 2015

You should get Packing with Python 3.5

The new Python 3.5 unpacking syntax makes a programmer’s life much easier.

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15 Nov 2015

To avoid Robocallers, use Pandas

I found a really neat data source online on unwanted robocalls that the FCC (Federal Communications Commission, a United States government agency) has created and published openly. The data source provides times and dates of unwanted robocalls that consumers have reported to the FCC. We can use this data source to find out all kinds of things, but today we will be content with just finding out the time of the day households are most likely to receive robocalls.

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08 Nov 2015

Parsing S-expressions with Python 3

This is a simple s-expression parser written in Python 3. It understands symbols and numbers and uses tuples to represent the data internally.

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01 Nov 2015

Tuples vs Lists in Python 3

Creating tuples from generator expression is surprisingly fast.

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25 Oct 2015

Filtering Trees

Today we are going to look at how to filter items in tree data structures using Python 3. We are going to compare a stateful approach and a functional and recursive approach. In the end we will discuss the advantages of a functional implementation.

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17 Oct 2015

Exploring Python dis

As you might know, CPython, the most commonly used implementation of Python, uses a stack based virtual machine to run Python scripts. This means that Python script ASTs are never directly executed. Instead, CPython compiles .py script files into byte code files first (.pyc files). This allows for some optimizations during the byte code compilation step and shipping of byte code files to end customers instead of raw scripts. This is useful to make reverse engineering hard. Ableton Live includes a CPython interpreter for its MIDI hardware integration. It does not let users look at the actual hardware integration scripts though. Instead, all hardware integration scripts can only be found in their compiled .pyc form.

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08 Oct 2015

Programmatically Accessing Cloud Photo APIs

This is a short evaluation on whether one can perform a series of basic tasks using the APIs that cloud photo services provide.

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17 Sep 2015

Using Async Functions in Python 3.5

With the new async syntax in Python 3.5, defining asynchronous functions has become a lot simpler. In this article, I will demonstrate a simple example for this new feature. It will involve pulling a set of homepages of popular websites and displaying the first 10 characters of every HTTP response. The example will utilize the awesome aiohttp library. Make sure that your machine has aiohttp and Python 3.5 installed.

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11 Sep 2015

5 Ways to Filter Items in Python 3

Given a list items, that contains ints and None, produce a list that only contains the int values with their order of appearance preserved.

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10 Sep 2015

Who To Sue If Skype Spam Kills You

The other day I received this ominous message on Skype from an infected machine:

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