Re: [Pyparsing] fixed-length field preceded by length?

[Paul M. <pt...@au...>]

John -

Sorry you were disappointed in GSWP; I had proposed a longer outline to
O'Reilly which included a reference section, but this would have inflated
the book beyond the 60-70 page length which was their ebook target at the
time.

Please take a look at how countedArray is implemented in the pyparsing code.
I think you could copy this method and write a countedLengthTextString
method using the same principles.

If you are still spinning your wheels, write back!

-- Paul
(There are docs, how-to's, UML diagrams, and many examples included in the
source distribution, please see if that material helps flesh out what you
didn't get from GSWP.  Also, there is online htmldoc (generated by epydoc)
at http://packages.python.org/pyparsing/, and a link to an HTML how-to at
http://pyparsing.svn.sourceforge.net/viewvc/pyparsing/src/HowToUsePyparsing.
html.)



-----Original Message-----
From: John W. Shipman [mailto:jo...@nm...] 
Sent: Saturday, December 31, 2011 2:40 PM
To: Pyp...@li...
Subject: [Pyparsing] fixed-length field preceded by length?

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

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