strange StopIteration issue, caused by old version of SWIG?

[JesusFreke]

This is a bit of a strange one. I was trying to generate a python generator function that yields the visible bodies from an occurrence and its child occurrences. But the script was failing with a StopIteration error that I couldn't explain.

import adsk.core
import adsk.fusion
import traceback

app = adsk.core.Application.get()
root = app.activeProduct.rootComponent

def box(x, y, z, *, name="Box"):
    brep = adsk.fusion.TemporaryBRepManager.get()
    box_body = brep.createBox(adsk.core.OrientedBoundingBox3D.create(
        adsk.core.Point3D.create(x/2, y/2, z/2),
        adsk.core.Vector3D.create(1, 0, 0),
        adsk.core.Vector3D.create(0, 1, 0),
        x, y, z))
    occurrence = root.occurrences.addNewComponent(adsk.core.Matrix3D.create())
    occurrence.component.name = name
    base_feature = occurrence.component.features.baseFeatures.add()
    base_feature.startEdit()
    occurrence.component.bRepBodies.add(box_body, base_feature)
    base_feature.finishEdit()
    return occurrence

def get_bodies(occurrence):
    for i in range(0, occurrence.bRepBodies.count):
        body = occurrence.bRepBodies.item(i)
        yield body
    for i in range(0, occurrence.childOccurrences.count):
        yield from get_bodies(occurrence.childOccurrences.item(i))

def run(context):
    try:
        first = box(1, 1, 1, name="first")
        second = box(1, 1, 1, name="second")
        second.moveToComponent(first)
        bodies = list(get_bodies(first))
        app.userInterface.messageBox("bodies: %d" % len(bodies))
    except:
        print(traceback.format_exc())
        app.userInterface.messageBox('Failed:\n{}'.format(traceback.format_exc()))

Which fails with the following exception

StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "generator_test.py", line 28, in get_bodies
 yield from get_bodies(occurrence.childOccurrences.item(i))
SystemError: <built-in function delete_Occurrence> returned a result with an error set

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "generator_test.py", line 35, in run
 bodies = list(get_bodies(first))
SystemError: <built-in function delete_BRepBody> returned a result with an error set

After doing a bit of googling, I suspect this is an issue with the version of swig used to generate the python api. See, e.g. https://github.com/swig/swig/pull/560. 

Based on the headers at webdeploy\production\<guid>\Api\Python\packages\adsk\core.py, it is using swig version 3.0.2, which predates the fix mentioned in the above bug.

Is there any chance you could update the swig version used to generate the python wrappers? 🙂

[JesusFreke]

Also, is this the best way to report api issues like this? If there's a different preferred way, I'll be happy to redirect my bug reports 🙂

[goyals]

Fusion using 3.0.2_a version of SWIG at present. There is no immediate plan to upgrade the version but I have created a task UP-40906 to track it in our internal bug tracking system and will update you if there is any update.

Posting any issue to forum is a good way in my opinion because others can also share their observations but you can contact me directly also at shyamsunder.goyal@autodesk.com if you have a specific API issue.

[JesusFreke]

Sounds good, thanks! I can stick with lists for now, but it would be nice to be able to use generators 🙂

[JesusFreke]

With the upgrade to Python 3.7, I was hoping SWIG might have been upgraded too. Unfortunately, it looks like it's still on 3.0.2, which is over 5 years old at this point, and I can still reproduce the StopIteration issue with the above script.

[goyals]

Upgrading to Python was looking more important than SWIG considering that there are not many issues reported so far with SWIG but we will definitely consider it in near future.

[JesusFreke · Accepted solution]

I saw in another post that the version of SWIG used had been updated for the latest version of Fusion 360. I just tried this script again and confirmed that the StopIteration issue is no longer present. Thanks!