old_contents: import tempfile
  import os.path as op
  import numpy as np
  import IPython.display as display
  
  import nibabel as nib
  from dipy.viz import fvtk
  from palettable.tableau import Tableau_20
  
  
  def visualize_bundles(trk, ren=None, inline=True, interact=False):
      """
      Visualize bundles in 3D using fvtk
  
  
      """
      if isinstance(trk, str):
          trk = nib.streamlines.load(trk)
  
      if ren is None:
          ren = fvtk.ren()
  
      for b in np.unique(trk.tractogram.data_per_streamline['bundle']):
          idx = np.where(trk.tractogram.data_per_streamline['bundle'] == b)[0]
          this_sl = list(trk.streamlines[idx])
          sl_actor = fvtk.line(this_sl, Tableau_20.colors[np.mod(20, int(b))])
          fvtk.add(ren, sl_actor)
  
      if inline:
          tdir = tempfile.gettempdir()
          fname = op.join(tdir, "fig.png")
          fvtk.record(ren, out_path=fname)
          display.display_png(display.Image(fname))
  
      if interact:
          fvtk.show(ren)
  
      return ren
  
new_contents: import tempfile
  import os.path as op
  import numpy as np
  import IPython.display as display
  
  import nibabel as nib
  from dipy.viz import fvtk
  from dipy.viz.colormap import line_colors
  
  from palettable.tableau import Tableau_20
  
  
  def visualize_bundles(trk, ren=None, inline=True, interact=False):
      """
      Visualize bundles in 3D using fvtk
  
  
      """
      if isinstance(trk, str):
          trk = nib.streamlines.load(trk)
  
      if ren is None:
          ren = fvtk.ren()
  
      # There are no bundles in here:
      if list(trk.tractogram.data_per_streamline.keys()) == []:
          streamlines = list(trk.streamlines)
          sl_actor = fvtk.line(streamlines, line_colors(streamlines))
          fvtk.add(ren, sl_actor)
  
      for b in np.unique(trk.tractogram.data_per_streamline['bundle']):
          idx = np.where(trk.tractogram.data_per_streamline['bundle'] == b)[0]
          this_sl = list(trk.streamlines[idx])
          sl_actor = fvtk.line(this_sl, Tableau_20.colors[np.mod(20, int(b))])
          fvtk.add(ren, sl_actor)
  
      if inline:
          tdir = tempfile.gettempdir()
          fname = op.join(tdir, "fig.png")
          fvtk.record(ren, out_path=fname)
          display.display_png(display.Image(fname))
  
      if interact:
          fvtk.show(ren)
  
      return ren
  
subject: Enable visualizing trk files without bundle designations.