I'm developing an web based application written in PHP5, which basically is an UI on top of a database. To give users a more flexible tool I want to embed a scripting language, so they can do more complex things like fire SQL queries, do loops and store data in variables and so on. In my business domain Python is widely used for scripting, but I'm also thinking of making a simple Domain Specific Language. The script has to wrap my existing PHP classes.
I'm seeking advise on how to approach this development task? 
Update: I'll try scripting in the database using PLPGSQL in PostgreSQL. This will do for now, but I can't use my PHP classes this way. Lua approach is appealing and seems what is what I want (besides its not Python).
You could do it without Python, by ie. parsing the user input for pre-defined "tags" and returning the result.
Embed python/dsl for scripting in an PHP web application