Thursday, April 24, 2014

Literate Programming with pyWeb 2.3

Updates completed. See and

The list of changes is extensive.

However, the essential API and the markup language for creating literate programs hasn't (significantly) changed. A few experimental features were replaced with a first-class implementation.

The interesting (to me) bit is this sequence of events.

I started out using Leo and Interscript as a literate programming tools. They worked. But they were larger and clunky and I wasn't happy.

I wrote my own too, not really getting the use cases.

I found pyLit and liked it a lot. For a long time, I liked it better than my own pyWeb tool.

Then I ran across some problem domains for which pyLit didn't work out well. It's not that I've abandoned pyLit, but I believe I'll focus more on pyWeb.

The Awkward Problem Domains

Here are the two awkward problem domains.

  • Historical Story Lines. In some cases, we want to describe a module or package based on the path of exploration. Rather than simply drop the design, we want to show the path followed which lead to the design. This can be helpful for certain kinds of pedagogical exercises where we're steering the reader through a process.
  • Complex Packages that Don't Follow Python's Presentation Order. In some cases, we need to present things out of order. Python constrains us to have docstring and imports first. Our class definitions must proceed in "dependency" order. But this may not be the best order for explanation. Sometimes, we want to start with the "def main():" function first to explain why a class looks the way it does.
PyWeb handles these nicely.  One of the handiest things is this for out-of-order presentation.

@d Some Class... @{
class TheClass:
    this class uses the following imports

@d Imports...@{
import this
import that

We can then scatter imports through the documentation in the relevant places. And they follow the more interesting material.

When it comes to final assembly, we have this.

@o @{
    @<Imports for this module@>
    @<Some Class that does the real work of this module@>
This builds the module, tangling the imports into one cluster up front, and putting the class definition later.