Justus Perlwitz

September 1, 2019

Hakyll on Netlify

If you are like me, you are more busy switching between static site generators than actually writing posts for your blog.

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January 11, 2019

Happy New Year, from Tokyo

On April 15 2018, I moved to Tokyo, Japan. I suppose that changed a few things in my life.

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May 4, 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 challenge 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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April 27, 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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April 20, 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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April 13, 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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April 6, 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.

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March 20, 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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March 9, 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.

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March 2, 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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February 23, 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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January 6, 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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December 29, 2017

transform()ing Like a Pro in Pandas

The Pandas API surprises me with a new feature or method almost every day, and I have yet again discovered an interesting piece of functionality.

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December 26, 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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December 23, 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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July 5, 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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June 30, 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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June 27, 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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June 15, 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.

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June 4, 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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April 25, 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.

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December 6, 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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November 30, 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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November 22, 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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November 15, 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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November 8, 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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November 1, 2015

Tuples vs Lists in Python 3

Creating tuples from generator expression is surprisingly fast.

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October 25, 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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October 17, 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.

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October 8, 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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September 17, 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.

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September 11, 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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September 10, 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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