I am seeing following issue:
In [5]: img = open_image("2018-09-21_005.hdr")
In [6]: view_cube(img, bands=[29, 19, 9])
ModuleNotFoundError                       Traceback (most recent call last)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/spectral/graphics/hypercube.py in 
     69 try:
---> 70     import wx
     71     from wx import glcanvas
ModuleNotFoundError: No module named 'wx'
During handling of the above exception, another exception occurred:
ImportError                               Traceback (most recent call last)
 in 
----> 1 view_cube(img, bands=[29, 19, 9])
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/spectral/graphics/graphics.py in view_cube(data, *args, **kwargs)
    176     to accept keyboard input.
    177     '''
--> 178     from spectral.graphics.hypercube import HypercubeWindow
    179
    180     if not running_ipython():
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/spectral/graphics/hypercube.py in 
     71     from wx import glcanvas
     72 except ImportError:
---> 73     raise ImportError("Required dependency wx.glcanvas not present")
     74
     75 DEFAULT_WIN_SIZE = (500, 500)           # Default dimensions of image frame
ImportError: Required dependency wx.glcanvas not present
I used following command to install wx:  "brew install wxpython"
The problem was related to installation of python package
Use following command to install by pip :
pip install wxpython
And Use following command to install by conda environment :
conda install wxpython
Unable to use view_cube command due to issue with wx