Question

I have a program which recieves inputs in the form of text for example :

IF (A.4.1-1/1 OR A.4.1-1/2) AND A.4.4-1/9 AND (A.4.4-1/12 OR A.4.4-1/13 OR A.4.4-1/14 OR A.4.4-1/15) THEN R ELSE N/A

where A.4.1-1/1 etc. are variables with a value TRUE or FALSE. so far i have parsed up the text into the logical parts for the above example I have a list that looks like this:

['IF', '(', 'A.4.1-1/1', 'OR', 'A.4.1-1/2', ')', 'AND', 'A.4.4-1/9', 'AND', '(', 'A.4.4-1/12', 'OR', 'A.4.4-1/13', 'OR', 'A.4.4-1/14', 'OR', 'A.4.4-1/15', ')', 'THEN', 'R', 'ELSE', 'N/A']

I am just wondering is it possible to actually perform the logic on this list like combine all this up into the rquired python statements and provide the result. I am not sure were to start I have read on some sites that I should use a top down parser??

Answer 1

This sounds like a task for Pyparsing:

The pyparsing module is an alternative
approach to creating and executing
simple grammars, vs. the traditional
lex/yacc approach, or the use of
regular expressions. The pyparsing
module provides a library of classes
that client code uses to construct the
grammar directly in Python code.

You will be able to quickly define your grammar (instead of playing with regular expressions) and specific parsing actions. I have built very rich mini-languages using Pyparsing in under 300 lines of code.