matplotlib runs but does not generate a graph

Question

I am trying to complete http://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_gui/py_image_display/py_image_display.html#using-matplotlib it runs but does not display anything

import numpy as np
import cv2
from matplotlib import pyplot as plt
img = cv2.imread('messi5.jpg',0)
plt.imshow(img, cmap = 'gray', interpolation = 'bicubic')
plt.xticks([]), plt.yticks([])  # to hide tick values on X and Y axis
plt.show()

(i am using a raspberry pi and followed this tutorial to install open cv http://www.pyimagesearch.com/2015/10/26/how-to-install-opencv-3-on-raspbian-jessie/ subsequently i pip installed matplotlib)

if i replace plt.show with plt.savefig it works what is wrong?

---

after adding import matplotlib; matplotlib.use('TkAgg') and import Tkinter or tkinter i get

    (cv) pi@raspberrypi:~/Desktop $ python tst4.py
Traceback (most recent call last):
  File "tst4.py", line 5, in <module>
   from matplotlib import pyplot as plt
 File "/home/pi/.virtualenvs/cv/lib/python3.4/site-    packages/matplotlib/pyplot.py", line 114, in <module>
   _backend_mod, new_figure_manager, draw_if_interactive, _show =       pylab_setup()
 File "/home/pi/.virtualenvs/cv/lib/python3.4/site-   packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
   globals(),locals(),[backend_name],0)
 File "/home/pi/.virtualenvs/cv/lib/python3.4/site-   packages/matplotlib/backends/backend_tkagg.py", line 13, in <module>
   import matplotlib.backends.tkagg as tkagg
File "/home/pi/.virtualenvs/cv/lib/python3.4/site-       packages/matplotlib/backends/tkagg.py", line 9, in <module>
  from matplotlib.backends import _tkagg
 ImportError: cannot import name '_tkagg'

Answer 1

I've ran into this issue myself. The problem is related to the matplotlib backend not being properly set within the virtual environment. It took me a lot of trial and error, but you first need to install a few dependencies:

$ sudo apt-get install tcl-dev tk-dev python-tk python3-tk

And then manually install matplotlib from source rather than using pip:

$ workon your_env_name
$ pip uninstall matplotlib
$ git clone https://github.com/matplotlib/matplotlib.git
$ cd matplotlib
$ python setup.py install

This should take care of the problem.

I detail my full experience and more details to the solution on this page.