[Python-Dev] Doctest and Footnotes

[Benji York]

A coworker of mine (Gary Poster) had a really good idea a couple weeks 
ago: teach doctest about ReST-style footnotes.  I implemented it over 
the weekend and brought it to Tim Peter's attention today.  Tim 
generally liked the idea and suggested I bring it up here.

Here's the idea: when a footnote is referenced in prose, execute the 
code associated with the footnote at that point.  For example:

"""
After initializing the system [#init]_ it is possible to retrieve status 
information:

     >>> system.status()
     'good to go'

[snip some of the doctest]

.. [#init] Initialize the system:
     >>> system = System()
     >>> system.init()
"""

The footnote code is executed every time the footnote is referenced, and 
is /not/ executed at any other time (i.e. it's not executed at the point 
the footnote is defined).  A warning is generated if a footnote (that 
includes code) is defined but never used.

This would allow moving repetitive or verbose code (e.g. tests for 
corner cases) into footnotes so they won't hinder the documentation 
aspect of a test.  It also allows defining reusable bits of setup code, 
freeing the doctest author to structure the prose as they wish instead 
of being constrained by having to place bits of code with common 
environmental needs together.

I've implemented this in a branch of zope.testing (which contains a copy 
of a post-Python 2.4.3 version of doctest (http://tinyurl.com/nekam). 
The behavior is controlled by an optionflag, much like ELLIPSIS or 
NORMALIZE_WHITESPACE.  Tim has given me a few pointers on improvements 
to make, which I'll work on this week.

Thoughts/questions?
-- 
Benji York
Senior Software Engineer
Zope Corporation