On Nov 27, 11:41 am, "Hendrik van Rooyen" <[EMAIL PROTECTED]> wrote: > "Steven D'Aprano" <steau> wrote: > > > > > Well, I don't know about "any problem". And it's not so much about > > whether metaprograms can solve problems that can't be solved by anything > > else, as whether metaprograms can solve problems more effectively than > > other techniques. > > > If you include factory functions, class factories, the builder design > > pattern, metaclasses, etc. as "metaprogramming", then I use it all the > > time, and find it an excellent technique to use. > > > But if you mean using a Python program to generate Python source code, > > then I can't think of any time I used it. Which doesn't mean that others > > don't find it helpful, only that I haven't yet. > > I am using the term in the restricted sense of Python writing Python source. > > Given that, can anybody think of an example that you could not do with > a class? (excepting the "stored procedure" aspect) > > Or can I claim a new a new meta - rule - I would call it van Rooyen's folly... > > > > > Thinking further back, when I was young and programming in Apple's > > Hypercard 4GL, I used to frequently use Hypercard scripts to generate new > > Hypercard scripts. That was to work around the limitations of the > > scripting language. > > What sort of stuff did you do, and would having had simple OO available > have rendered it unnecessary? > > > > > I don't think metaprogramming in the limited sense (programs to output > > source code) is a bad idea, but I do think that there are probably better > > alternatives in a language like Python. > > True. No argument here - I was just wondering if the relationship holds. > > - Hendrik
"Given that, can anybody think of an example that you could not do with a class?" Generating a template for a specific script application. For example, a script with pre-defined callbacks that only require the addition of the contents. I was really interested in exploring the idea of using python output, instead of XML, to record something a user did in a GUI. I have seen it done and it is really advantageous in the 3D industry because it means the script files can be edited directly, in a pinch, to generate something slightly different. For example, say we have code which generates a cube by plotting it's points. A user then changes a point position in the GUI. The change is saved by outputting the function call to a file with new arguments (the new point location). If I wanted to make 100s of copies of the cube, but with a slightly different point position, I could edit the custom cube's python code and hand it back for creation without using the GUI. I could do this with XML, but it can be harder to work with in a text editor (though I have seen some XML editors that make it a bit easier.) In fact, in most 3D applications, the app prints everything the user does to a log. Sometimes in a choice of languages, so I guess I am looking to do the same thing with my own custom tools. In a real situation the generated code file can build some pretty complex 3D object hierarchies. It moves beyond simple storage of data and becomes a real script that can be hacked as necessary. It is nice to have everything as python scripts because we always have a blend of GUI users and developers to get a job done. - Rafe -- http://mail.python.org/mailman/listinfo/python-list
