code: def no_tvtk():
      """Checks if tvtk was found"""
      global _have_tvtk
      return not _have_tvtk
  
file_path: nipype/nipype/interfaces/vtkbase.py
imports: import os
  from ..None import logging
label_desc: Use image node_id 3 for calling a global function with example usage: no_tvtk() and returns: unknown