[Python] vtkExtractUnstructuredGrid not producing any output in the paraview python shell

Hi I'm trying to convert a vtkUnstructuredGrid object read from a .case file into paraview and use the vtkExtractUnstructuredGrid filter to convert it to a vtkPolyData so that I can then use various polydata filters to get the connectivities of all faces and edges of my mesh. (this is for a fancy edge based cfd solver)

The input mesh is a 2x2x2 cube of eight hexahedral elements spanning from 0,0,0 to 4,4,4 with 27 points that is read as a vtkUnstructuredGrid.

vtkUnstructuredGrid (000001BD37601910)
Debug: Off
Modified Time: 2255684
Reference Count: 2
Registered Events: (none)
Information: 000001BD2BA69970
Data Released: False
Global Release Data: Off
UpdateTime: 0
Field Data:
Debug: Off
Modified Time: 2255656
Reference Count: 1
Registered Events: (none)
Number Of Arrays: 0
Number Of Components: 0
Number Of Tuples: 0
Number Of Points: 27
Number Of Cells: 8


The relivant code is below, where fluidblock is my unstructured grid and polyblock is meant to be my polydata output.

print (fluidBlock)
polyblock = vtkPolyData()
polycon=vtkExtractUnstructuredGrid()
polycon.SetInputData(fluidBlock)
polycon.SetOutput(polyblock)
print(polyblock)


Polyblock is assigned as a polydata somewhere but it has not inherited any data from the unstructured grid. I know this is just me being unfamiliar with the syntax of the vtk library but Its stumped me for the better part of a day.

vtkPolyData (000001BD2B5F8A80)
Debug: Off
Modified Time: 2256455
Reference Count: 2
Registered Events: (none)
Information: 000001BD2BA68240
Data Released: False
Global Release Data: Off
UpdateTime: 0
Field Data:
Debug: Off
Modified Time: 2256452
Reference Count: 1
Registered Events: (none)
Number Of Arrays: 0
Number Of Components: 0
Number Of Tuples: 0
Number Of Points: 0
Number Of Cells: 0


If anyone can tell me what I'm doing wrong that would be appreciated.

It's worth mentioning that really my end goal here is being able to extract a list of all unique faces and edges in my mesh (ie such that the two faces and four edges two hexahedral elements share are counted as one) and I'm not particular about methods, that is to say: if anyone has a better way to extract this data using the vtk library than messing with polydata please tell me.

Apologies for the amateurish question python is not my best language.

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