[Tutor] parsing?

[Danny Yoo]

On Fri, 29 Jun 2001, Roeland Rengelink wrote:

> > I'm tying to make something that can read some values and functions
> from a file > and then use these to create a parametric surface in
> triangles to be rendered > by POV-Ray. The triangle generation isn't
> the problem, but reading the > functions into the program. >
> 
> Unfortunately, in general this is not trivial.
>
> 
> Presumably, the file you read contains statements in some kind of
> programming language. It is certainly possible to build a parser in
> Python for that language which then allows you to execute those
> statements in Python, as it were. This is not easy, and may not be the
> right solution anyway.


It sounds like something that dealt with rexec would be a good Useless
Python challenge; an example might make it easier to adjust it to do
parameteric surface stuff.  Here's an idea for such a challenge:


It'd be great if we had a program that acts like a numerical integrator.  
We'd be able to give this program some function, and have it do something
that a TI calculator might be able to do.

If we put on our "wishing makes it so" cap, we can imagine that running
Integrator might look like this:

###
[dyoo@einfall] ./Integrator.py
Hello, I'm a simple numerical integrator.  For help, please type 'help'
at the prompt.

> help
Hello, this is the help file for Integrator.  Here are a list of commands
you can do with me:

    'list'
           --- print out a list of functions we can integrate

    'integrate([function], [left-point], [right-point])'
           --- Return the numerical integration of a particular function, 
               starting from the left-point to the right-point.

    'load([file])'
           --- Load a function into the integrator.

    'help'
           --- You're looking at it.     

    'quit'
           --- you'll need to quit.

> load('FyMathFunction.py')           # Let's pretend that we have an
                                      # MyMathFunction.py that
                                      # contains a one-argument function.
Ok, I've loaded MyMathFunction().

> list
[MyMathFunction]

> integrate(MyMathFunction, 0, 10)
42
###


The MyMathFunction.py file itself would contain something like:

###
def MyMathFunction(x):
    return 4.2
###

but of course, Integrator.py should be able to handle more interesting
functions.


I don't think I have time to write this at the moment, but perhaps someone
else can work on this one.