On 27 Nov., 06:11, Rafe <[EMAIL PROTECTED]> wrote: > 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
A rather advanced approach to deal with "writing XML in Python" and generating "Python from XML" has been chosen in P4D: http://pypi.python.org/pypi/P4D%20Langlet/1.2.4 It is of course a cultural mismatch to do such stuff because it targets a proper superset of Python but I don't think it's worse than what has been done in a plethora of template languages ( P4D is none of them though ), YAML or related approaches. I did it mostly because I wanted to learn Adobe Flex and I wanted to use it as a scripting language, not as something I had to edit in a particular editor like FlexBuilder. -- http://mail.python.org/mailman/listinfo/python-list
