particle impot

Hello, everyone.
I made a sample of the particles before the model was run. After the sample preparation, I want to import the particles through the example provided by script [1]. I ran the following three lines in the program:

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From Yade import export

VtkExporter = export. VTKExporter ('/tmp/vtkExporter Testing')

VtkExporter. exportSpheres (what = Dict (dist ='b. state. pos. norm ()')

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However, after the operation, the following errors occurred:

ValueError Traceback (most recent call last)
/usr/bin/yadedaily in <module>()
----> 1 vtkExporter.exportSpheres(what=dict(dist='b.state.pos.norm()'))

/usr/lib/x86_64-linux-gnu/yadedaily/py/yade/export.py in exportSpheres(self, ids, what, comment, numLabel, useRef)
    428 outFile.write("%g\n"%(b.shape.radius))
    429 # write additional data from 'what' param
--> 430 for name,command in what: # for each name...
    431 test = eval(command) # ... eval one example to see what type (float, Vector3, Matrix3) the result is ...
    432 # ... and write appropriate header line and loop over all bodies and write appropriate vtk line(s)

ValueError: too many values to unpack
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I would appreciate it if you could give me some advice.