Show Trimesh method returns AttributeError

I am using the trimesh Python library to manipulate and analyze triangular meshes. The method call show()

returns the AttributeError attribute:

import trimesh
mesh = trimesh.load_mesh("myfile.stl")
mesh.show()

Traceback (most recent call last):
  File "/Users/cg/anaconda/lib/python2.7/site-packages/IPython/core/interactiveshell.py", line 2881, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-5-cbb52bec63cc>", line 1, in <module>
    mesh.show()
  File "/Users/cg/anaconda/lib/python2.7/site-packages/trimesh/base.py", line 1339, in show
    scene.show(**kwargs)
  File "/Users/cg/anaconda/lib/python2.7/site-packages/trimesh/scene/scene.py", line 383, in show
    viewer()
  File "/Users/cg/anaconda/lib/python2.7/site-packages/trimesh/scene/scene.py", line 380, in viewer
    SceneViewer(self, **kwargs)
  File "/Users/cg/anaconda/lib/python2.7/site-packages/trimesh/scene/viewer.py", line 31, in __init__
    self.reset_view(flags=flags)
  File "/Users/cg/anaconda/lib/python2.7/site-packages/trimesh/scene/viewer.py", line 125, in reset_view
    if (self.width is not None and
  File "/Users/cg/anaconda/lib/python2.7/site-packages/pyglet/window/__init__.py", line 850, in <lambda>
    width = property(lambda self: self.get_size()[0],
  File "/Users/cg/anaconda/lib/python2.7/site-packages/pyglet/window/cocoa/__init__.py", line 398, in get_size
    window_frame = self._nswindow.frame()
AttributeError: 'NoneType' object has no attribute 'frame'

      

        
        
        
      

    

I am using Python 2.7.11 and OSX 10.11. Has anyone faced a similar problem?