In rails, there exists this feature where you can bind an object to an action such that, if for example - someone submit a web form, you can programatically require that certain fields are non-empty and match a given criteria (e.g. only digits).

Does Pylons have this type of ability?

In rails, I believe the code would look something like this:

class User < ActiveRecord::Base validates_presence_of :username, :message => 'is required' validates_presence_of :email, :message => 'is required' end

Which would require a "username" and "email" and if not present, an error message would be displayed saying that it "is required".