Newbie Question. Class definitions on the fly.

[hiaips]

ishtar2020 wrote:
> Hi everyone
>
> I'm sure this question is kinda stupid and has been answered a few
> times before... but I need your help!
>
>  I'm writing a small application where the user can analyze some text
> based on a set of changing conditions , and right now I'm stuck on a
> point where I'd like to automatically generate new classes that operate
> based on those user-defined conditions.
>
> Is there a way in python to define a class in runtime? For instance,
> can I define a class which extends another(that I have previously
> defined in some module) , create some instance completely on the fly
> and then add/redefine methods to it?
>
> If affirmative, I've thought of a problem I would maybe have to face:
> as the class has been defined by direct input to the python
> interpreter, I could only create instances of it on the same session I
> entered the definition(because it's not on a module I can load on
> future uses) but not afterwards.  Is there a way to keep that code?
>
> Even more newbie paranoia: what would happen if I make that 'on the
> fly" object persist via pickle? Where would Python find the code to
> handle it once unpickled on another session (once again, i take that no
> code with the definition of that instance would exist, as it was never
> stored on a module).
>
> Hope it wasn't too ridiculous an idea.
>
> Thank you for your time, guys.

You might check out the following link on metaclass programming:

http://www-128.ibm.com/developerworks/linux/library/l-pymeta.html

The author gives at least one short example of creating a class
dynamically and using an instance of it. There are also links to other,
related articles and topics at the bottom.

--dave