Python FAQ

Frequently asked questions about how to write Python scripts for Slicer.

How to find a Python function for any Slicer features

All features of Slicer are available via Python scripts. Slicer script repository contains examples for the most commonly used features.

To find out what Python commands correspond to a feature that is visible on the graphical user interface, search in Slicer’s source code where that text occurs, find the corresponding widget or action name, then search for that widget or action name in the source code to find out what commands it triggers.

Complete example: How to emulate selection of FOV, spacing match Volumes checkbox in the slice view controller menu?

  • Go to Slicer project repository on github
  • Enter text that you see on the GUI near the function that you want to use. In this case, enter "FOV, spacing match Volumes" (adding quotes around the text makes sure it finds that exact text)
  • Usually the text is found in a .ui file, in this case it is in qMRMLSliceControllerWidget.ui, open the file
  • Find the text in the page, and look up what is the name of the widget or action that it is associated with - in this case it is an action named actionSliceModelModeVolumes
  • Search for that widget or action name in the repository, you should find a source file(s) that use it. In this case it will is qMRMLSliceControllerWidget.cxx
  • Search for the action/widget name, and you’ll find what it does - in this case it calls setSliceModelModeVolumes method, which calls this->setSliceModelMode(vtkMRMLSliceNode::SliceResolutionMatchVolumes), which then calls d->MRMLSliceNode->SetSliceResolutionMode(mode)
  • This means that this action calls someSliceNode->SetSliceResolutionMode(vtkMRMLSliceNode::SliceResolutionMatchVolumes) in Python syntax it is someSliceNode.SetSliceResolutionMode(slicer.vtkMRMLSliceNode.SliceResolutionMatchVolumes). For example, for the red slice node this will be:
sliceNode = slicer.mrmlScene.GetNodeByID('vtkMRMLSliceNodeRed')