Parsing files in python

[Chris Angelico]

On Mon, Dec 24, 2012 at 9:32 PM, Kene Meniru <Kene.Meniru at illom.org> wrote:
> You are saying I can create a python module that can parse this file format
> without using a system like python-ply? I know how to parse strings using
> python but considering that text files that describe a whole building may be
> quite large I thought perhaps the re module may not be adequate.

Effectively, what you do is leverage the Python parser. Your script
would look like this:

------------possible user file content for parsing ------------
# Boiler-plate to make this work
from pypovray import *

# in the following the python interface program reads
# the contents of the file "other.file" as if its content
# were located at this point.
import other.file

#In the following the python interface makes "snap_size" a
#  global parameter
snap_size = 10


# In the following "buildingLevel" is a class (or function) 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))
------------end of user file content

Note the extreme similarity to your original example. Everything
between the two snip-lines is perfectly legal Python code. (The
semantics of a Python import aren't quite the same as a C preprocessor
#include, so that might need a little tweaking, depending on what you
wanted to achieve there. Possibly "from other.file import *" would do
it.) Instead of writing a file parser, with all the complexities that
that entails, all you need to write is a set of functions/classes that
can be invoked.

The only part that doesn't work cleanly is the vector, since its
syntax doesn't work in Python. You'll need to use round brackets
instead of angle ones, as in the above example, and on output to
Python, translate them. But that's fairly straight-forward, and by
this method, you get *everything else* done for you - parsing, nesting
of function calls, the entire Python standard library... the works.

ChrisA