Re: [Pyparsing] Variable comment char

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

That *does* seem weird, that the comment character can be changed on the fly
like that.

I would use a self-modifying expression, similar to what you see in the
pyparsing code for matchPreviousLiteral or countedArray.  In this case, you
would define the comment expression as a Forward() and initialize it to the
default comment character (let's say it's '#').

comment = Forward()
comment << '#' + restOfLine

Use expr.ignore(comment) just as you normally would.  Then define your
comment redefinition expression as:

redefine_comment = "[Comment char]" + oneOf(list(printables))("newchar") +
"_char"

And attach a parse action to redefine_comment like this:

def redefine_current_comment_char(tokens):
    comment << tokens.newchar + restOfLine

I've never tried dynamically modifying an expression that gets ignored, you
might have to do something else like Ralph Corderoy suggested, breaking up
the input text into multiple "[Comment char]"-controlled blocks, parse each
one separately, and then merge the results back together.  Fortunately, the
merging of results is very easy now, you can just put them into a list and
combine them using:

    all_results = sum(list_of_results)

Good luck!
-- Paul
 


-----Original Message-----
From: Russell Dill [mailto:Rus...@as...] 
Sent: Sunday, September 25, 2011 9:29 PM
To: pyp...@li...
Subject: [Pyparsing] Variable comment char

I need to parse a rather evil format that has the following line:

[Comment Char] |_char

Which would change the comment char to '|'. The comment char can be
any non-alphanumeric printable other than [ or ] and the comment char
...