Thursday, April 09, 2009

Through the Interface: AutoCAD and IronPython

Kean Walmsley, of the "Through the Interface" blog, is an AutoCAD programmer who has been meaning to try out Python for some time. He is somewhat sceptical of dynamic typing, but has heard many good things about Python:
Python is also of interest because of its cross-platform availability: it’s an open source language with its roots in the UNIX/Linux world, but is now gaining popularity across a variety of OS platforms (one of the reasons it’s the scripting language chosen for at least one of our cross-platform products, Autodesk Maya).
He has a (short) series of blog entries on getting IronPython (and IronRuby) working with AutoCAD.
I had originally hoped to build a .NET assembly directly using IronPython – something that appears to have been enabled with the 2.0 release of IronPython - which could then be loaded into AutoCAD. Unfortunately this was an exercise in frustration: AutoCAD makes heavy use of custom attributes for identifying commands etc., but IronPython doesn’t currently support the use of attributes.

Then, thankfully, Tim Riley came to the rescue: we’ve been in touch on and off over the years since he started the PyAcad.NET project to run IronPython code inside AutoCAD, and Tim was able to put together some working code which actually registered commands (after I’d pointed him at a function he could use from AutoCAD 2009’s acmgdinternal.dll – an unsupported assembly that exposes some otherwise quite helpful functions). He ended up choosing an implementation that had also been suggested to me by Albert Szilvasy: to implement a PYLOAD command using C# which allows selection and loading of a Python script (because Python is, ultimately, all about scripting rather than building static, compiled assemblies).
After getting my feet wet in the last post with my first IronPython application running inside AutoCAD, I decided it was time to attack a slightly more challenging problem: jigging a database-resident Solid3d object. The idea had come after I’d received a question by email from David Wolfe, who wanted to have a fully rendered 3D view of a cylinder he was jigging.
From what I can tell – and I’m really a newbie in both these languages – there is relatively little to separate the two: both Ruby and Python have their devotees but they ultimately to belong to different sects of the same faith (it’s hard to escape religious analogies when talking about programming languages, for some reason :-). That said, the fiercest arguments often seem to occur between people who very nearly agree. This is not something I know enough about to get involved in – even if I wished to – so I’m going to steer well clear of it, and simply show some simple Ruby code that does the same as in the equivalent post for IronPython. If you Google “python ruby comparison” you should find plenty of opinions out there.

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