How Would You Do: Parsing and Expression Evaluation

[Paul McGuire]

"Al Christians" <achrist at easystreet.com> wrote in message
news:108rren1js1hn71 at corp.supernews.com...
> I've got an idea for an application, and I wonder how much of what it
> takes to create it is available in open source python components.
>
> My plan is this -- I want to do a simple spreadsheet-like application:
> I've used a wxGrid, so I expect that wxPython will do fine for the user
> interface.   The spreadsheet can be organized vertically, one item per
> line.  It might need no more than 100 rows or so.  On each line, the
> user will enter in one column an item (variable) name and, in another
> column, a formula or  expression for computing the item's value.  A
> third column will show the computed value.   There will usually be some
> circular references between the items, but their values will converge
> quickly with repeated evaluation.
>
> The final feature is a button that the user can click when they have the
> sheet set up correctly -- it will translate the formulas into simple C
> and python code to perform the same calculations as the spreadsheet.
>
> The formulas should be pretty easy -- add, subtract, multiply, divide,
> log, exponential,  and perhaps some user-defined functions.
>
> Are there any off-the-shelf python libraries that would make this kind
> of app much easier?  I don't have any special experience related to such
> things, so I surely don't want to re-invent the wheel out of pure
> ignorance -- should I try the parsing tools in the standard python
> library, or will something else work better for me?
>
> TIA for any advice,
>
>
> Al

One of the examples that comes with pyparsing is a simple 4-function
expression parser and evaluator, that is easily extendable to add
exponentiation and user-defined functions.

Download pyparsing at http://pyparsing.sourceforge.net .

-- Paul