[solved] hasattr at LinkGroup.ViewObject causes FreeCAD crash ?

[dprojects]

Hi, anyone can confirm this is FreeCAD bug?

For LinkGroup this code below causes FreeCAD crash at ViewObject:

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import FreeCAD

lg = FreeCAD.ActiveDocument.getObjectsByLabel("LinkGroup")[0]
vo = lg.ViewObject
d = dir(vo)

for o in d:
	FreeCAD.Console.PrintMessage("\n")
	FreeCAD.Console.PrintMessage(str(o))
	hasattr(vo, o)

For stable version:

Code: Select all

OS: Ubuntu 22.04 LTS (XFCE/xubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 0.20)
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.9.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods: 
  * Woodworking 0.20.29177

This is also at latest FreeCAD version:

Code: Select all

OS: Ubuntu 22.04 LTS (XFCE/xubuntu)
Word size of FreeCAD: 64-bit
Version: 0.21.29485 (Git) AppImage
Build type: Release
Branch: master
Hash: a236ca843fdd6674afb6d7ed1454fbd3b547f5ea
Python 3.10.5, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods: 
  * Woodworking 0.20.29177

[Roy_043]

Confirmed:

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>>> d = dir(vo)
>>> for o in d:
...  hasattr(vo, o)
... 
True
True
True
True
True
True
True

Traceback (most recent call last):
  File "<input>", line 2, in <module>
Base.FreeCADError: Unknown exception while reading attribute 'DraggingPlacement' of object 'ViewProviderLink'

Code: Select all

OS: Windows 8.1 (6.3)
Word size of FreeCAD: 64-bit
Version: 0.21.29485 (Git)
Build type: Release
Branch: master
Hash: a236ca843fdd6674afb6d7ed1454fbd3b547f5ea
Python 3.8.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: Dutch/Netherlands (nl_NL)
Installed mods: 

[dprojects]

Yes, this crash FreeCAD also from python console manually, not only from macro. Also the getattr make crash too:

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Document
<GUI Document object at 0x562879352250>

any workaround?

EDIT:

Removing "DraggingPlacement" works, but I am not sure if this is correct solution. What is there at DraggingPlacement?

Code: Select all

import FreeCAD

lg = FreeCAD.ActiveDocument.getObjectsByLabel("LinkGroup")[0]
vo = lg.ViewObject
d = dir(vo)

for o in d:
	if str(o).find("DraggingPlacement") == -1:
		FreeCAD.Console.PrintMessage("\n")
		FreeCAD.Console.PrintMessage(str(o))
		hasattr(vo, o)

[wmayer]

There is a failing assert() in FreeCAD/src/Gui/ViewProviderLink.cpp inside the function Base::Placement Gui::ViewProviderLink::currentDraggingPlacement():

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Base::Placement ViewProviderLink::currentDraggingPlacement() const{
    assert(pcDragger); // <<<=== pcDragger is null
    SbVec3f v;
...
}

This can be easily fixed by removing the assert() and doing some null pointer checks instead.

[wmayer]

git commit 3f8dc1a5a8

@uwestoehr
Please backport that one.

[dprojects]

@wmayer Thanks Werner for this fix, the C ++ scares me a bit

Is there any way to get the LinkGroup.ViewObject.DraggingPlacement ?
Even if you run from python console

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lg = FreeCAD.ActiveDocument.getObjectsByLabel("LinkGroup")[0]
vo = lg.ViewObject
vo.ViewObject.DraggingPlacement 

the FreeCAD crash. So how to deal with such things in the future? the try and except will not work too in this case. Any workaround for future?

[uwestoehr]

Please backport that one.

Done.
(FYI: I also started to look once a week through the commits what can/should be backported to not miss things.)

[wmayer]

Is there any way to get the LinkGroup.ViewObject.DraggingPlacement ?
Even if you run from python console

You have to start the "Transform" edit mode as:

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vo.Document.setEdit(vo, 1) # the number 1 means Transform
vo.DraggingPlacement 

[dprojects]

You have to start the "Transform" edit mode as:

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vo.Document.setEdit(vo, 1) # the number 1 means Transform
vo.DraggingPlacement 

This works but I was rather thinking about global solution to avoid FreeCAD crashes from python.

I use the hasattr at each ViewObject property in scanObjects inspection tool. I can see the DraggingPlacement is there because of dir(ViewObject) but if I want to go deeper to see what is inside ViewObject I have to call hasattr at each property and then the FreeCAD crash. Because I am trying to call hasattr at DraggingPlacement.

Maybe there is possibility (I don't know FreeCAD and C++ so well) to add some kind of sandbox function? similar to translate maybe? Something like FreeCAD.sandbox("any python command to run it safely without FreeCAD crash"). If someone would like to run something safely, there would be possibility to run it thru sandbox function?

Thanks for your help and sorry for long post, I know you probably don't have time to read long stories.

[wmayer]

This works but I was rather thinking about global solution to avoid FreeCAD crashes from python.

That's not possible. If there is a C++ function that doesn't do correct error-checking and thus causes a segmentation fault or a failing assert() then the application crashes. And it doesn't make a difference whether this function is called from another C++ function or from Python.