code: def do_track(self, arg):
          
          try:
              from rpython.translator.tool.reftracker import track
          except ImportError:
              print('** cannot import pypy.translator.tool.reftracker **',
                    file=self.stdout)
              return
          try:
              val = self._getval(arg)
          except:
              pass
          else:
              track(val)
docs: track expression
  
          Display a graph showing which objects are referred by the
          value of the expression.  This command requires pypy to be in
          the current PYTHONPATH.