[vtkusers] When must I be weary of Python garbage collection?

[David Gobbi]

On Wed, Feb 24, 2016 at 2:46 AM, Elvis Stansvik <
elvis.stansvik at orexplore.com> wrote:
>
>
> So my question is, can I always rely on this behavior when working with
> pipelines through the Python wrappers? Or are there cases where VTK will do
> things in C++ "behind the back" of the Python garbage collector?
>

Yes, you can rely on this behavior.  As expected, the vtkRenderWindow C++
object holds a reference to the renderer, which holds references, to the
actors, etc.

The Python wrappers provide a python "wrapper" object for each C++ object
that is exposed to python.  At the end of the scope, the reference count of
the python object is decref'd.  If this causes the python object to
destruct, then the reference count of the underlying C++ object is
decref'd.  The underlying C++ object destructs if its reference count
reaches zero.



> And in fact, most of the time you probably want to keep references to a
> lot of things, to be able to reconfigure the pipeline. I'm just wondering
> if there are any gotchas to watch out for wrt to garbage collection when
> not keeping references. If there are any "best practices" so to speak.
>

There are no best practices, because garbage collection is something that
most users are not supposed to worry about.

Because garbage collection is done via reference counting, sometimes gc is
delayed due to reference cycles.  But both VTK and Python have cycle
detection in their garbage collectors.

 - David
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