[chimera-dev] Re: Xform

[Greg Couch]

FYI, the classes that are passed by reference all subclass from
otf::WrapPy<>, and you effectively get a reference to the C++ instance in
the Python instance.  For other classes you get a copy of the C++
instance, but get normal Python reference semantics on the result.  Ignore
the "WRAP CLASS" comment, it is for wrapping classes that are not in the
target namespace.

	- Greg

On Wed, 14 May 2003, Thomas Goddard wrote:

> Hi Steve,
>
>   The model.openState.xform is guaranteed to be a copy of the
> transform object.  Other Chimera objects returned as attribute lookups
> are also always copies, including Point, Vector, BBox.  Some objects
> are never copied like Atom, Bond, Molecule - you always get a
> reference.  It may be that the "WRAP CLASS" comment in the pyinterface
> file is what marks Xform, Point, ... as objects that are always passed
> by value between Chimera's Python and C++ layers.  Greg Couch
> (gregc at cgl.ucsf.edu) is the one who would know if this is right.
>
>   I will be implementing an "undo move" menu item.  I think many people
> will appreciate that.
>
>     Tom
>
>
> > Date: Wed, 14 May 2003 01:20:26 -0500 (CDT)
> > From: Steve Ludtke <stevel at blake.3dem.bioch.bcm.tmc.edu>
> > Reply-To: sludtke at bcm.tmc.edu
> > To: Thomas Goddard <goddard at cgl.ucsf.edu>
> >
> > Hi again. Thanks for that include file. It's been answering most of my
> > questions. I'm putting something together I like quite a lot, and I've
> > taken care of the problem that was making me wish for an undo. As part of
> > this, though, I've come up with a technical question. What are the copying
> > semantics for Xform objects ? ie -
> >
> > mx=mod.openState.xform
> > (user rotates model)
> > mx still has the original value
> >
> > This is good, but counter to the typical behavior of objects in python.
> > That is, I would expect mx to point to an Xform object, and as long as the
> > same Xform object gets reused when the model is rotated, I should see the
> > rotated values rather than the original values. I'm not complaining, what
> > it does is actually what I'd like it to do. The question is, can I rely on
> > this behavior, or do I need to make a copy of the Xform object to make
> > sure it won't change on me. Is it just happenstance that a new object is
> > getting created upon rotation ? If I need to make a copy, how should I do
> > it ?  Will normal deep-copying python methods work ?
> >
> > As usual. Thanks for the assistance. Perhaps I'll produce something to our
> > mutual benefit  :^)
> >
> > --
> > ----------------------------------------------------------------------------
> > Steven Ludtke, PhD              |        Baylor College of Medicine
> > sludtke at bcm.tmc.edu             |               Co-Director
> > stevel at alumni.caltech.edu       | National Center For Macromolecular Imaging
> > V: (713)798-6989                |    Dept of Biochemistry and Mol. Biol.
> > instant messenger: sludtke42    |            * Those who do ARE *
> > http://ncmi.bcm.tmc.edu/~stevel |           The converse also holds
> >
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