This example demonstrates how to run Grow from seeds effect in batch mode (without GUI, using qMRMLSegmentEditorWidget) using 3D Slicer

SegmentGrowCutSimple.py

# Generate input data
################################################

import SampleData

# Load master volume
sampleDataLogic = SampleData.SampleDataLogic()
masterVolumeNode = sampleDataLogic.downloadMRBrainTumor1()

# Create segmentation
segmentationNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLSegmentationNode")
segmentationNode.CreateDefaultDisplayNodes() # only needed for display
segmentationNode.SetReferenceImageGeometryParameterFromVolumeNode(masterVolumeNode)

# Create seed segment inside tumor
tumorSeed = vtk.vtkSphereSource()
tumorSeed.SetCenter(-6, 30, 28)
tumorSeed.SetRadius(10)
tumorSeed.Update()
segmentationNode.AddSegmentFromClosedSurfaceRepresentation(tumorSeed.GetOutput(), "Tumor", [1.0,0.0,0.0])

# Create seed segment outside tumor
backgroundSeedPositions = [[0,65,32], [1, -14, 30], [0, 28, -7], [0,30,64], [31, 33, 27], [-42, 30, 27]]
append = vtk.vtkAppendPolyData()
for backgroundSeedPosition in backgroundSeedPositions:
  backgroundSeed = vtk.vtkSphereSource()
  backgroundSeed.SetCenter(backgroundSeedPosition)
  backgroundSeed.SetRadius(10)
  backgroundSeed.Update()
  append.AddInputData(backgroundSeed.GetOutput())

append.Update()
backgroundSegmentId = segmentationNode.AddSegmentFromClosedSurfaceRepresentation(append.GetOutput(), "Background", [0.0,1.0,0.0])

# Run filter
################################################

# Create segment editor to get access to effects
segmentEditorWidget = slicer.qMRMLSegmentEditorWidget()
# To show segment editor widget (useful for debugging): segmentEditorWidget.show()
segmentEditorWidget.setMRMLScene(slicer.mrmlScene)

segmentEditorNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLSegmentEditorNode")
segmentEditorWidget.setMRMLSegmentEditorNode(segmentEditorNode)
segmentEditorWidget.setSegmentationNode(segmentationNode)
segmentEditorWidget.setMasterVolumeNode(masterVolumeNode)

# Run segmentation
segmentEditorWidget.setActiveEffectByName("Grow from seeds")
effect = segmentEditorWidget.activeEffect()
# You can change parameters by calling: effect.setParameter("MyParameterName", someValue)
# Most effect don't have onPreview, you can just call onApply
effect.self().onPreview()
effect.self().onApply()

# Clean up and show results
################################################

# Clean up
slicer.mrmlScene.RemoveNode(segmentEditorNode)

# Make segmentation results nicely visible in 3D
segmentationDisplayNode = segmentationNode.GetDisplayNode()
segmentationDisplayNode.SetSegmentVisibility(backgroundSegmentId, False)

When I run this code using my own CT data, there is an error as follows. How can I solve it?
File "qt-scripted-modules\SegmentEditorEffects\AbstractScriptedSegmentEditorAutoCompleteEffect.py", line 301, in onApply
previewContainsClosedSurfaceRepresentation = previewNode.GetSegmentation().ContainsRepresentation(
AttributeError: 'NoneType' object has no attribute 'GetSegmentation'