code: def example_data(infile="functional.nii"):
      """returns path to empty example data files for doc tests
      it will raise an exception if filename is not in the directory"""
  
      filepath = os.path.abspath(__file__)
      basedir = os.path.dirname(filepath)
      outfile = os.path.join(basedir, "data", infile)
      if not os.path.exists(outfile):
          raise OSError("%s empty data file does NOT exist" % outfile)
  
      return outfile
  
label_desc: Use image node_id 1 for calling a global function with example usage: example_data(infile) and returns: outfile