Re: [Pyparsing] Parsing Stanford Polygon File Format (PLY)

[E Y. <you...@gm...>]

Hi all,

it took a while, but I managed to complete an initial working version of
the PLY parser thanks to Paul's suggestions. The self-contained example you
can find here:
https://gist.github.com/youngec/76c5b552ab5bc04b43d1bfa9d3fa0a78. Its only
dependency is the python package attrs (https://pypi.org/pypi/attrs),
because it makes python classes a bit easier to manage. You're free to use
that parser as you wish.

The parser is part of a larger project at
https://github.com/youngec/rootspace/tree/develop, and the respective unit
tests are at
https://github.com/youngec/rootspace/blob/develop/src/rootspace/tests/test_parsers.py
.

Theres one big caveat to the parser though, and I'm hoping you can provide
some guidance: Currently, it only understands ASCII-based PLY files, but
doesn't understand the two much more common binary formats (little- and
big-endian). Can pyparsing handle binary data?

Thanks so much!

Best,
Ellie


On 24 December 2016 at 06:48, <pt...@au...> wrote:

> >
> > first off, I would like to thank the developer(s) for making such a great
> > tool. It's such an elegant piece of work!
>
> Thank you - flattery is always a good start! I'm glad pyparsing has been
> helpful for you, and that you find it to your liking.
>
> Kudos on your posted parser - starting with posting your BNF! So many
> people skip this step, and then get mired down in distracting details, and
> find they have overlooked or skipped significant parts. I'm also glad to
> see that you are using the new pyparsing_common expressions. I had some
> mixed feelings about including them, and your sample code shows them being
> put to good use.
>
> >
> > Though, I'm happy if somebody can provide some help. I'm trying to
> > implement a Standford polygon file parser (
> > http://paulbourke.net/dataformats/ply/), but I'm having trouble getting
> it
> > to parse the file into the correct data structure, because parts of the
> > file depend on depend on declarations earlier in the same file.
> >
>
> This happens often enough, and there are several examples of such adaptive
> parsers that I have posted over the years. The main concept is to define a
> Forward for the part of the parser that needs to be adaptive, and then to
> use a parse action attached to the part with the format description to
> create the flexible part of the parser, and to then insert it into the
> placeholder Forward using the '<<' operator.
>
> I touched up your parser from the gist that you posted, and have added
> some sample code that will parse the test cube example. You can find it
> here: https://gist.github.com/anonymous/4498de5ce91da8cf4292bad408076b97
> I think you'll be able to take it from there. (I also applied some
> stylistic changes - removing explicit .setResultsName calls in favor of
> implicit callable notation, changing CaselessLiteral to CaselessKeyword, a
> Group added here or there for better structure and results name assignment.
> Feel free to keep any, all, or none of these changes.)
>
> Please post a link to your finished project to this list, or the Pyparsing
> Facebook page.
>
> Regards,
> -- Paul McGuire
>
>
>
>
>