Hi, Tom: On Monday, July 23, 2001, at 10:32 AM, "Tom Cameron" < wrote:0000,0000,DEB7 I am starting to experiment with ZClasses, and hopefully eventually Products in Python. I am wondering how easy it is to migrate at a later date. I asked a similar question a while ago. Here is the response I got from"Joachim Werner" <: 0000,6363,1212And while I'm on that topic, what are the benefits/tradeoffs between using the ZMI to define products and using Python? 0000,0000,DEDE Some of the main reasons to use Python-based products are - much better performance (ZClasses just "emulate" object behaviour; e.g. all sub-objects are actually just put into propertysheets) - being able to do much more things (e.g. calling Python libraries like the Python Imaging Library etc.) - avoiding problems with ZClasses (e.g. acquisition works not quite as advertised, multiple inheritance: base classes can only be defined at creation time and not changed later, inheritance does not work properly for propertysheets defined in ZClass-type base classes, ...) 0000,6363,1212Also, if I decide to go with Python based products, is there any easy way to turn a ZClass defined though the ZMI into a Python product? I'm not to worried about retyping code, but I've defined some fairly large propertysheets that would be annoying to recreate if I were to start from scratch. 0000,0000,DEDE It is not extremely hard to write a ZClass-to-Python code converter. But AFAIK there is no such beast yet. If you don't need the extra power Python gives you, you might be better off with them. Your programming will be magintudes faster using ZClasses (while the resulting code will be much slower ...), provided that you don't hit the limitations of ZClasses. We at iuveno are facing similar problems and are working at tools for making Zope product creation much easier. Most of it is not ready for use yet. But I'd ask you to tell me what you would expect from a "better Zope product definition framework" or whatever you'd call it. Just to give you an impression about our ideas, here are some of them: - Definition of REAL Python-based classes over the web (like ZClasses); everything I mention below should also work with these new over-the-web classes - Being able to define template-like classes (like "Meta-ZClasses"); e.g. you'd have a predefined "Persons" ZClass and could use it to derive a special "Co-Workers" or "Customers" class by just adding/changing stuff - Wizards for the basic tasks (like creating a new ZClass; you'd not have to click through all the definition tabs after the basic creation of the ZClass); the wizards framework exists already - Defining basic "components" like data class, presentation class, etc. - A forms builder framework (with the help of Martijn Faassen's Formulator, this part is quite advanced already) - being able to define objects from UML tools - roundtrip engineering (from UML tools etc. to Zope and back); there already are tools to get ZClass structures into the Object Domains UML software ... - providing a lot of frequently needed basic modules to the programmer/power user; the Content Management Framework is a basic attempt to do this Cheers Joachim 0000,0000,DEB7 In any case I am expecting that the Product will be continually evolving. How are instances affected when new versions of products are installed? Instances will use your new class definitions. However, new member variables that you add will not be defined in current instances. The trick is to define default values for new variables as class variables, and override them them with self.new_variable = new_value whenever you update them. I switched over to Python products after creating only a couple of ZClasses. While getting off the ground with ZClasses is a lot easier, in the long run you'll be better off with Python products (depending on your level of comfort with Python). If you are interested in getting started with Python classes, I highly recommend Max M's A very minimal Product (http://www.zope.org/Members/maxm/HowTo/minimal_01/) and A Minimal Product - The Sequel (http://www.zope.org/Members/maxm/HowTo/minimal_02/). Once you've gone through these tutorials, read chapter 3 (http://www.zope.org/Documentation/ZDG/Products.dtml) of the Zope Developer's Guide (http://www.zope.org/Documentation/ZDG). Assuming you don't have to many methods in your ZClass, converting isn't to hard to do by hand. Just turn all of your Python scripts into methods and each of your DTML documents/methods into files in a 'dtml' folder inside your product folder. Then import them using DTMLFile (Max M. shows you how. Don't forget the .dtml extension on your DTML files!) As far as I'm aware, changing a ZClass over to Python will break all of your existing instances, unfortunately. You could write a script to convert them, blah, blah. But who wants to do that? It's better to do it in Python in the first place (but get to know ZClasses first, just don't put to much work into them). One thing I like about Python classes is the ability to add custom Security Declarations (i.e., defining custom permission names; the Products chapter of the Zope Developer's Guide gets into this). Good luck! -- Mark James Adams mark@raysend.com