Example of a systemd service file

Here is an almost-minimal example of a systemd service file, that I use to run the Mastodon bot of my generative art playground Graft.

I made a dedicated user just to run this service, and installed Graft into /home/graft/apps/graft under that username. Now, as root, I edited a file called /etc/systemd/service/graft.service and made it look like this:

[Service]
ExecStart=/home/graft/apps/graft/bot-mastodon
User=graft
Group=graft
WorkingDirectory=/home/graft/apps/graft/
[Install]
WantedBy=multi-user.target

Now I can start the graft service like any other service like this:

sudo systemctl start graft

and find out its status with:

sudo systemctl status graft

If I want it to run on startup I can do:

sudo systemctl enable graft

and it will. Easy!

If I want to look at its output, it’s:

sudo journalctl -u graft

As a reward for reading this far, here’s a little animation you can make with Graft:

How to write a programming language articles

Recent Overload journal issues contain my new articles on How to Write a Programming Language.

Part 1: How to Write a Programming Language: Part 1, The Lexer

Part 2: How to Write a Programming Language: Part 2, The Parser

PDF of the latest issue: Overload 146 containing part 2.

This is all creative-commons licensed and developed in public at github.com/andybalaam/articles-how-to-write-a-programming-language

TECH(K)NOW Day workshop on “Writing a programming language”

My OpenMarket colleagues and I ran a workshop at TECH(K)NOW Day on how to write your own programming language:

A big thank you to my colleagues from OpenMarket who volunteered to help: Rowan, Jenny, Zach, James and Elliot.

An extra thank you to Zach and Elliott for their impromptu help on the information desk for attendees:

Hopefully the attendees enjoyed it and learned a bit:

You can find the workshop slides, the full code, info about another simple language called Cell, and lots more links here: github.com/andybalaam/videos-write-your-own-language, my blog at artificialworlds.net/blog, and follow me on twitter @andybalaam.

Thanks to OpenMarket for supporting us in running this workshop!

Adding a day in Python datetimes – use timedelta, not the datetime constructor

If you want “tomorrow” in Python datetimes, don’t construct a datetime like this:

from datetime import datetime, timedelta
td = datetime.today()
tm1 = datetime(td.year, td.month, td.day + 1, 14, 0, 0)
# Don't do this!

Because it will work sometimes, but fail when today is the last day of the month:

Traceback (most recent call last):
  File "./tomorrow", line 6, in 
    tm1 = datetime(td.year, td.month, td.day + 1, 14, 0, 0)
ValueError: day is out of range for month

Instead, use Python’s timedelta, which is designed for this purpose:

from datetime import datetime, timedelta

td = datetime.today()
tm2 = td + timedelta(days=1)

print("tm2=%s" % str(tm2))

And it’s easier to read too.

Broken Levels Challenge – Egham Raspberry Pi Jam July 2017

Today at the Egham Raspberry Pi Jam we did two things:

1. The Broken Levels Challenge

Some nasty person came and broke our levels for our game Rabbit Escape and we need you to fix them!

To play this game you will need a PC version of Rabbit Escape, our Broken Levels, and the instruction sheets. Let us know how you get on!

2. Python Traffic Lights Programming Workshop

I ran a workshop to learn a bit of Python programming using this resource sheet Pi Stop Traffic Lights.

We had a lot of fun, and hopefully some people even learnt a little bit of coding.