Using Conda Environments and the Fish Shell

I recently started over with a fresh development environment and decided to try something new: I’m using Python 3 via miniconda. The first real hiccup I’ve run into is that conda’s environment activation/deactivation scheme only works in bash or zsh. I use fish. There is an open PR to get fish support for conda but in the meantime I hacked something together to help me out.

"Activating" a conda environment does a couple of things:

  • Puts the environment’s "bin" directory at the front of the PATH environment variable.
  • Sets a CONDA_DEFAULT_ENV environment variable that tells conda in which environment to do things when none is specified.
  • Adds the environment name to the prompt ala virtualenv.

Deactivating the environment resets everything to its pre-activation state. The fish functions I put together work like this:

~ > type python
python is /Users/---/miniconda3/bin/python
~ > condactivate env-name
(env-name) ~ > type python
python is /Users/---/miniconda3/envs/env-name/bin/python
(env-name) ~ > deactivate
~ > type python
python is /Users/---/miniconda3/bin/python

Here’s the text of the functions:

Or you can download it from

To use these, add them to the ~/.config/fish/ directory and source them from the end of the ~/.config/fish/ file:

source $HOME/.config/fish/

Making Commits via the GitHub API

For fun I’ve been learning a bit about the GitHub API. Using the API it’s possible to do just about everything you can do on GitHub itself, from commenting on PRs to adding commits to a repo. Here I’m going to show how to do add commits to a repo on GitHub. A notebook demonstrating things with code is available here, but you may want to read this post first for the high level view.

Choosing a Client Library

The GitHub API is an HTTP interface so you can talk to it via any tool that speaks HTTP, including things like curl. To make programming with the API simpler there are a number of libraries that allow communicate with GitHub via means native to whatever language you’re using. I’m using Python and I went with the library based on its Python 3 compatibility, active development, and good documentation.

Making Commits

The repository api is the gateway for doing anything to a repo. In this is corresponds to the repository module.

Modifying a Single File

The special case of making a commit affecting a single file is much simpler than affecting multiple files. Creating, updating, and deleting a file can be done via a single API call once you have enough information to specify what you want done.

Modifying Multiple Files

Making a commit affecting multiple files requires making multiple API calls and some understanding of Git’s internal data store. That’s because to change multiple files you have to add all the changes to the repo one at a time before making a commit. The process is outlined in full in the API docs about Git data.

I should note that I think deleting multiple files in a single commit requires a slightly different procedure, one I’ll cover in another post.

That’s the overview, look over the notebook for the code!

Writing WordPress Posts in Markdown

Pen and Pants is hosted by WordPress, but I write my blog posts in my favorite text editor using Markdown. That way I have all the conveniences those afford and I can archive the posts in plain text on GitHub.

The tricky part is going from the .md files to some text I can paste into the input box in WordPress. I learned today that you can write posts in Markdown, but that still doesn’t work perfectly for me because WordPress treats new lines within blocks as hard breaks. (When writing posts I break all lines before 80 characters for more convenient editing and diffing. Keeping all those breaks literal doesn’t translate well to web pages.)

Today, thanks to Ethan White, I figured out that Pandoc can help. By converting my Markdown to Markdown with the --no-wrap flag Pandoc will output paragraphs on a single line but otherwise give me regular Markdown. The command I use looks like this:

pandoc -f markdown -t markdown --no-wrap

I can take the output of that and past it into WordPress’ text input box (after ticking the box to allow Markdown when writing posts).

Note that if you use fenced codeblocks (as on GitHub) WordPress will convert that into its special source code widget. If instead you want something presented using only <pre><code> tags then use indentation to indicate it is pre-formatted text.

Tips for Mac Users

If you use Homebrew you can install Pandoc via the cask add on:

brew cask install pandoc

To copy the output of pandoc straight to the clipboard you can use the pbcopy command:

pandoc -f markdown -t markdown --no-wrap | pbcopy

The Libraries of

In this post I’ll describe the libraries used by to turn requests into web pages and JSON to send back to users. In some future posts I’ll describe how it’s actually put on the internet. If you’re curious about the code you can see it on GitHub.

Back End

The back end consists of GET and POST REST endpoints for ipythonblocks to talk to and handlers for the site itself: main and about pages, a random grid redirect, and the individual grid views. In all there are about six handlers for all of

Framework is such a simple site that any lightweight framework could probably handle it. I went with Tornado mainly because I’ve used it before and I like the way applications are designed using Tornado. That it includes a template engine and a high performance web server are also pluses. If I’d not used Tornado, Flask and Jinja2 would have been my second choice.


Choosing a database was something of an agonizing decision. You can choose from SQL, NoSQL, and key-value stores; and within each of those you have many more choices. I like the simplicity of working with schema-less databases like MongoDB, and I was very intrigued by RethinkDB, but in the interest of having a simple setup that allowed me to focus on developing app logic I ended up using sqlite. I use the dataset library to take care of some of the SQL overhead (like table creation) so that I can combine the simplicity of sqlite with a more NoSQL-like interface.

At some point I may want to move to another database, especially one running on a dedicated machine so that swapping the application server can be done without worrying about the database. When I get to that point I’ll probably take another look at RethinkDB and see if it’s ready for my application.

To avoid database lookups of recently visited pages I’m using memcached and talking to it from Python via the pylibmc library.


Python’s built in logging can certainly get the job done, but its interface has some rough edges I don’t like. Configuration can be painful for sophisticated cases and any kind of structured logging requires custom formatting. I think Twiggy is a much more “Pythonic” approach to logging with simpler configuration and built in structured logging. was my first time using Twiggy and I’d use it again. (Though it is unfortunately not Python 3 compatible at this time.)


Requests to the POST endpoint are validated using jsonschema. This provides protection for the app against incorrectly configured requests and can be used as a kind of documentation on what requests should look like.

I use the hashids library to turn the integer SQL IDs of grid entries into short strings, as in This is a URL form people are familiar with and it allows the implementation of “secret” grid posts that have public URLs but are difficult to find unless someone gives you the URL.

Users of ipythonblocks can include code with their posted grids and I use Pygments to highlight the syntax of the code and format it for HTML. Pygments is decent enough to escape HTML included in the posted code so I don’t have to worry about that breaking the page rendering. The color scheme used is Base16 Chalk Light via

Finally, I use ipythonblocks itself to turn grid data into rendered HTML via the same methods used by the IPython Notebook.

Front End

The back end renders and delivers static HTML to browsers (or JSON to ipythonblocks) so there isn’t much fancy going on in the front end. I use CSS media queries to adjust the site margins for small screens, and on the front page I use Pure CSS grids to make a responsive three-column layout that collapses to a single column on small screens. uses the Source family of fonts from Adobe delivered by Google Fonts.


Way back…

About a year ago, inspired by Greg Wilson, I wrote ipythonblocks as a fun way for students (and anyone else!) to practice writing Python with immediate, step-by-step, visual feedback about what their code is doing. When I’ve taught using ipythonblocks it has always been a hit—people love making things they can see. And after making things people love to share them.

Sometime last year Tracy Teal suggested I make a site where students could post their work from ipythonblocks, share it, and even grab the work of others to remix. Today I’m happy to announce that that site is live:

How it works

With the latest release of ipythonblocks students can use post_to_web and from_web methods to interact with post_to_web can include code cells from the notebook so the creation process can be shared, not just the final result. from_web can pull a grid from for a student to remix locally. See this notebook for a demonstration.

Thank you

There are many people to thank for helping to make possible. Thanks to Tracy Teal for the original idea, thanks to Rackspace and Jesse Noller for providing hosting, and thanks to Kyle Kelley for helping with ops and deployment.  Most of all, thanks to my family for putting up with me working at a startup and taking on projects.