Nathan Yergler

July 19, 2017

TFW you’re trying to fix an inconsistency, find & fix a bug, only to realize that if that’s the only bug it would have been broken everywhere.

Nathan Yergler

July 18, 2017

A week from today I’ll be on my way to Lincoln, Nebraska for a five day printmaking working at Constellation Studios. Feeling excited, feeling nervous, feeling ready.

Spent the afternoon in the studio yesterday, carving and printing my third Red Rocks print. I’ve been trying to get practice in with my new tools and this piece definitely provided that. I learned a lot from making it; on to the next exercise. 

Exactly Once Delivery

At Remind I helped build the announcement and chat message delivery platform. With thousands of messages streaming through a system that bridged Heroku and our AWS VPC, network partition and other failures were real occurrences, which led to some creative work ensuring messages were only delivered once to each recipient. So I was interested to see two articles posted within a day of each other talking about “exactly once delivery”.

TL;DR: It’s really hard, a lot of the systems wind up looking alike (ie, two-phase ack), and the one we built probably wasn’t as bullet proof as we thought. The interesting question wasn’t “Are we doubling up?” or “Are we dropping things?”, but “How will we know when either happens?”

Link
The Busy Trap

Tim Kreider writes:

Idleness is not just a vacation, an indulgence or a vice; it is as indispensable to the brain as vitamin D is to the body, and deprived of it we suffer a mental affliction as disfiguring as rickets. The space and quiet that idleness provides is a necessary condition for standing back from life and seeing it whole, for making unexpected connections and waiting for the wild summer lightning strikes of inspiration — it is, paradoxically, necessary to getting any work done.

There’s a voice in my head that says curiosity has to have an outcome, that if there isn’t something to show at the end, it’s not worth exploring. Nice to be reminded there are other perspectives.

Tower

I was in the studio last week, printing a new piece, the Tower Theater. Despite taking the source photo eighteen months ago, I only started drawing and carving a week before printing. I’ve been feeling a little out of practice, so I wanted to do something in the way of practice: something that would give me some practice carving, getting the feel for my tools back, without letting myself get too caught up in what the outcome was going to be. And all in all, I’m pretty pleased with the result: there are things I see that I’d do differently, but as I read in Art & Fear, every piece has the seed of the next piece in it.

Technical documentation with Tut

Long running branches are a personal pet peeve of mine: I’d much rather put the effort into managing feature flags, etc than I would into merging a branch that’s diverged significantly. So it’s with a mixture of embarrassment and relief that today I merged a branch that’s been hanging out for 3 years.

Four years ago I published Effective Django. As I was writing it, I knew I wanted to version control the text. As I worked with the code samples, however, it felt like I was having to work against my version control, rather than having it work for me: the code changes as the reader works through the content, and that’s not necessarily the same sequence of changes I’d make as I wrote. In effect, there were two timelines at work, and they didn’t match up. To make matters worse, it felt like I was repeating myself a lot: copying and pasting between source files when I wanted to start a new “chapter”, etc. Tut was my solution to this problem.

When I started updating Effective Django three years ago, I was aware there was still room for improvement: my Restructured Text source files were littered with specific line numbers from the source code, as well as prepend, pyobject, and end-before flags for my literal includes, all for the purpose of limiting the display to the changes. These felt brittle and inelegant: if I made a change in an early step of the tutorial (which tut made easy), all the line numbers could conceivably change; missing one was the sort of error that’s difficult to check without incredibly careful proofreading. It seemed like I should be able to get that information from the source control, so I set out to figure out how.


I think of the Effective Django tutorial, written using the first iteration of tut, as a form of “executable documentation”. It contains code samples, and the fact that those exist independently on disk means you can conceivably go to any point in time and run tests to make sure things are working. My first exposure to executable documentation was doctests; indeed, when I started thinking about tut, the place I started was reading the code for Sphinx’s doctest support.

As I thought about how to make my code inclusion more robust, I thought I wanted a “literate tut”: that is, a single document that contained both the text and source, from which I would weave the files if I wanted to execute them. I probably tried half a dozen approaches to make this work. Some “wove” the source files at Sphinx build time, another tried to marry Jupyter kernels with a Sphinx builder. In the end none of them worked perfectly, and — perhaps more importantly — none of them felt easy to author with. I knew I wasn’t going to use a tool for very long if it made life harder, no matter how elegant its approach.

Defeated, I decided to go back to where I started: using tut to manager source changes, but dropping the “tricks” I’d used to make inclusion work right. In other words, I stopped trying to be clever and just started writing.


In the years since I started the “literate tut” branch, I had made some improvements that seemed worth keeping around. I’d abstracted the git operations slightly and removed a lot of the global state. I’d also moved from trying to “infer” the order of steps based on history to maintaining an explicit list in a special configuration branch. These changes meant that as I started writing — and making progress — it was easier to try out a couple of ideas.

When Tut encounters a “checkpoint” it switches to a different git branch. This means that if the source tree is dirty, the build won’t succeed. After running into that a handful of times, I realized that I could use the same approach I used for fetching configuration (git show) to fetch a file from a specific branch, which potentially eliminates the need for playing chutes and ladders with head.

This got me thinking that I could grab two different versions of a file for side by side display, if I so desired. Combined with Python’s difflib module, however, it suddenly seemed like I had the basis for generating the sort of “documentation style” diffs I’d so tediously hand crafted before.


The result of this work is Tut 0.5, released today just over four years (!!) since the last release. This release includes a lot of changes, and is what I’m using as I work on an updated Effective Django, but I’m primarily releasing it to get the branch closed and focus myself on what else might be needed.

This release includes a new tut:literalinclude directive which operates exactly like the built-in one, with the exception that the content is read from git, not the filesystem. I’ve also added a tut:diff directive, which is able to format diffs for Python source files that do a reasonable(-ish) job of only showing the context that’s needed. The tut:diff directive can also show a link to the full file at that stage, so the entire contents are readily available.


I don’t think it’ll be another four years until the next release. As I work on the Effective Django update, I’m pretty sure I’ll need to improve diff generation and make it behave reasonably for non-Python files.

I thought I wanted “literate tut”: a single document that contained the diffs and text all in one. What I wound up with is something better: the ability to use the right tools to edit the text and code, and the ability to leverage the underlying framework to include exactly what I want as I write. You can find the new release of tut on PyPI; let me know what you think.