Re: Parsing files in python

Discussion in 'Python' started by Terry Reedy, Dec 24, 2012.

  1. Terry Reedy

    Terry Reedy Guest

    On 12/23/2012 12:19 PM, Kene Meniru wrote:
    > Hello: I am writing a program that is made up of a collection of
    > POV-Ray macros. POV-Ray is available at It is a
    > ray-tracing program that reads a scene description language (SDL) to
    > create photo-realistic images. At this time my program (for modeling
    > building information) is so huge that I am finding it difficult
    > managing the macros and I am not even near completion.
    > I am hoping to move this program to python and am wondering the best
    > way to approach this.
    > I would like to model my program after LaTeX. Basically the user
    > writes a text file using certain key words and numbers and my python
    > program reads this file, calls the classes that will then work
    > together to calculate the information that is needed to create an
    > accurate model. The result of this calculation will be an output to
    > another text file in the appropriate format such as POV-Ray SDL,
    > OpenSCAD script, etc. This file output can then be rendered by the
    > corresponding program to produce the actual 3D model. The macros I
    > have now currently does this but like I said it is getting tedious
    > and most importantly the fun factor is losing its strength for me.
    > I have been advised to check out python-ply and I have come across
    > others. I have not really tried any yet and before I dive into any
    > one of them I was wondering what else I should know. The following is
    > a sample of what the text file that will be processed by this
    > proposed system will contain. I appreciate any pointers and
    > suggestions.

    Mine is "Don't do that." Seriously. What I understand is that you are
    proposing to design and write a parser for yet another Domain Specific
    Language -- that will require knowledge to use that is useless outside
    the specific domain. I expect that is will come to duplicate the basic
    facilities of existing languages. Users will want to be able to
    calculate, make conditional calculations and constructions, iterate*,
    and define functions (subroutines, macros). Why bother to reinvent all
    that? It often becomes a mess. (Or you will offer or people will want to
    mix Python with the dsl. That also can become a mess.)

    Instead, write a pypovray package incorporating the POV macros, that can
    be imported into a python program. Write a tutorial for the specific
    parts of Python that users will need.

    For instances, someone wants to place duplicate or parameterized models
    on a rectangular grid, along an arc, or even at random locations.

    > ------------possible user file content for parsing ------------ // in
    > the following the python interface program reads //+ the contents of
    > the file "other.file" as if its content //+ were located at this
    > point.

    # this is a python comment. trivial difference from //
    > include other.file

    import other.file # with Python's variations
    # or
    exec(open('other.file')) # but it is nearly always better to
    # keep the separate namespace. What if a name in other.file
    # is the same as used below?
    import pypovray as ppr

    > //In the following the python interface makes "snap_size" a //+
    > global parameter
    > declare snap_size = 10

    snap_size = 10 # the extra word is just noise

    > // In the following "buildingLevel" is a class that is //+ called
    > and passed the parameters in parenthesis. buildingLevel("FirstLevel",
    > 3000)
    > // In the following "snapOffset" is a class that is //+ called and
    > passed the parameters in parenthesis.

    > snapOffset("Closet-S1_r1", "Closet-S2_r3", <0,0,0>)

    Already legal Python

    # at the end of the file

    # Reads globals(), which python has nicely created for you, to create
    the master scene description and output whatever is needed for povray.
    It could be part of a file you provide.

    Terry Jan Reedy
    Terry Reedy, Dec 24, 2012
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