August bpython sprint

31 Aug 2014

I just took a vacation for a week! I spend time with my family in Washington State mostly doing fun outdoorsy things. I didn’t answer email for the week but I did try to get some work in on bpython: only as much as was fun to do at the time. I made a list of issues1 to try to tackle and chose the deadline of the first day of the next batch of Hacker School to finish them. I only have half of the original tasks checked off so far and still have today and tomorrow to improve that ratio, but I wanted to do a retrospective while I had time and they were fresh on my mind.

What I got done

  1. Readline kill and yank in bpython

    I got to learn all about the readline kill buffer for this issue. In bpython we don’t use readline in order to process keyspresses one at a time, which a lot of reimplementing readline ourselves.2 I had to change the way our readline keybindings get assigned in code to let readline edit functions return what was just killed. I’m pretty happy with how this turned out, and think it’ll be useful in the future.

    It turns out multiple kills with the same readline kill command add to the kill buffer cumulatively! I wasn’t aware of this feature until I bothered to read some readline docs. I included this in our kill / yank feature and am already finding it useful.

  2. Open config in bpython

    You can now open your bpython config from bpython! It’s F3 by default. Increasing discoverablility of config options was the goal here, alongside the new help feature which shows all keybindings (F1 by default). Since we already had all the tools in place for launching an eternal editor, increasing use of the config file will hopefully be worth the feature creep.

  3. Readline-style incremental search

This is a feature many people have asked for (though except for rntz they’ve been anonymous folks from irc): ctrl-r and ctrl-s should work as they do in readline. Like the readline kill buffer, working on it opened my eyes to the legacy of readline - effective use of the command line is a skill useful at a scale larger than programming languages, and obeying UX conventions like readline enable folks experienced. My implementation is similar to that of bash, but does highlighting differently and matches all locations on a given line simultaneously, more like fish-style up arrow completion.

We still have to decide who to dissapoint with the default keybindings: longtime bpython users who expect ctrl-r to be rewind and ctrl-s to be save or users that expect these keys to work as they do almost everywhere else. For the moment the incremental search functionality is on meta-r and meta-s.

  1. Repl painting tests

I’ve been causing a lot of regressions in our not-very-well-tested codebase so I’m very excited to start recording the behavior of bpython like this to prevent these regressions. Adding a custom diff display to curtsies made this pretty fun:

diff example

  1. Travis CI

Another source of regressions for me is failing to test everything in all of the Python versions we support (Python 2.6, 2.7, 3.3, and 3.4). Running our tests in all environments is certainly possible to do locally (I use tox to do this) but having the extra, automatic check is nice. It was fun to push their terminal emulator to the limit:

I also fixed a few issues that the intrepid master branch-using myint found, closed an issue I’d opened as not actually useful, and cleaned up some tests.

What I didn’t get done

  1. Autoindent and autocompletion for multiline commands

Originally brought up because they would make monkeypatching in completion and highlighting possible in bpython for Hy, I didn’t want to work on these because they would require refactoring existing parenthesis counting code in bpython that didn’t look like fun to touch.

  1. Support for ASCII terminals

Figuring out how to test this didn’t seem fun, but by narrowing the scope of the bug from “fix encodings” to “make ascii work,” I feel pretty good about tackling it soon.

  1. Clear screen bug

This bug looks pretty involved, it’s for a feature I don’t like much (the temporary “Welcome to bpython” banner), and it might change completely if the we ever start using a separate process for bpython (which isn’t going to be until after the next release). I’ll probably pair with someone on it next week: it’s the kind of bug that I don’t trust myself to understand fully without collaboratively building and externally communicating that udnerstanding.

  1. Help browser in bpython

I though I knew how to go about this, but was thrown for a loop by some limitations I forgot terminals had with regard to saving the current session and putting a fullscreen window over it. A few false starts have given me the understanding of the problem I need to tackle it in the future.

So what’s the point?

There isn’t much of one - I just wanted a chance to reflect on the work I had done. I’m still cogitating on what lessons to take from this work. I’ll probably crib from this post a bit for the changelog in the next bpython release.

It is interesting to see the fun pieces get done and the less fun ones not, and to think about what makes some programming tasks more enjoyable than others.

I’m very grateful to folks like myint who are running master and reporting bugs - if you’d like to join them check out the contributing docs!

  1. I did add a few things to the sprint retroactively that I wanted to talk about here, work I did the weekend before I was on vacation.

  2. I don’t entirely understand how readline works so I’m not confident we shouldn’t be using it somehow. We may go as far as implementing readline vi keybindings and using user preferences from .inputrc in the future, so it would sure be nice to harness it.