Programmatically converting/parsing LaTeX code to plain text

Question

I have a couple of code projects in C++/Python in which LaTeX-format descriptions and labels are used to generate PDF documentation or graphs made using LaTeX+pstricks. However, we also have some plain text outputs, such as an HTML version of the documentation (I already have code to write minimal markup for that) and a non-TeX-enabled plot renderer.

For these I would like to eliminate the TeX markup that is necessary for e.g. representing physical units. This includes non-breaking (thin) spaces, \text, \mathrm etc. It would also be nice to parse down things like \frac{#1}{#2} into #1/#2 for the plain text output (and use MathJax for the HTML). Due to the system that we've got at the moment, I need to be able to do this from Python, i.e. ideally I'm looking for a Python package, but a non-Python executable which I can call from Python and catch the output string would also be fine.

I'm aware of the similar question on the TeX StackExchange site, but there weren't any really programmatic solutions to that: I've looked at detex, plasTeX and pytex, which they all seem a bit dead and don't really do what I need: programmatic conversion of a TeX string to a representative plain text string.

I could try writing a basic TeX parser using e.g. pyparsing, but a) that might be pitfall-laden and help would be appreciated and b) surely someone has tried that before, or knows of a way to hook into TeX itself to get a better result?

Update: Thanks for all the answers... it does indeed seem to be a bit of an awkward request! I can make do with less than general parsing of LaTeX, but the reason for considering a parser rather than a load of regexes in a loop is that I want to be able to handle nested macros and multi-arg macros nicely, and get the brace matching to work properly. Then I can e.g. reduce txt-irrelevant macros like \text and \mathrm first, and handle txt-relevant ones like \frac last... maybe even with appropriate parentheses! Well, I can dream... for now regexes are not doing such a terrible job.

Answer 1

A word of caution: It is much more difficult to write a complete parser for plain TeX than what you might think. The TeX-level (not LaTeX) \def command actually extends TeX's syntax. For example, \def\foo #1.{{\bf #1}} will expand \foo goo. into goo - Notice that the dot became a delimiter for the foo macro! Therefore, if you have to deal with any form of TeX, without restrictions on which packages may be used, it is not recommended to rely on simple parsing. You need TeX rendering. catdvi is what I use, although it is not perfect.