[Pyparsing] fixed-length field preceded by length?

[John W. S. <jo...@nm...>]

I'm trying to parse the .calendar file used by the old Unix ical
calendar program (the one written by Sanjay Ghemawat, not any of
the modern iCal utilities).

Here is a typical line from this file:

Text [6 [Easter]]

As you can see, the length is given explicitly, followed by
whitespace, and the text string in brackets.

How do I write the pyparsing syntax for lines of this form?
The length may be any number, and I'd like to handle the
case where '[' or ']' characters occur inside the text
string.

It's quite straightforward to write the patterns, but how
do I write the pattern for the text string in such a way
that it gets the length from a previous token in the
same pattern?

I just paid $10 for Paul McGuire's "Getting Started" eBook
and was quite disappointed that there's no reference section,
and no obvious solution to my problem.

Any suggestions?

Best regards (and happy new year!),
John Shipman (jo...@nm...), Applications Specialist, NM Tech Computer Center,
Speare 146, Socorro, NM 87801, (575) 835-5735, http://www.nmt.edu/~john
   ``Let's go outside and commiserate with nature.''  --Dave Farber