I have started to play with Python and I went directly to Python 3.6.
I have two Python environments now in my system: Python 2..6.6 and Python 3.6
Python 2.6.6 is under: 
which python
/usr/bin/python
And Python 3.6 is under /opt/python3/bin
My problem is that if I try to import tkinter in Python 3.6 it does not work:
./python3.6
Python 3.6.0 (default, Feb 16 2017, 17:37:36)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux
Type "help", "copyright", "credits" or "license" for more information.



import tkinter
      Traceback (most recent call last):
        File "", line 1, in 
        File "/opt/python3/lib/python3.6/tkinter/init.py", line 36, in 
          import _tkinter # If this fails your Python may not be configured for Tk
      ModuleNotFoundError: ****No module named '_tkinter'****



If I do in Python 2.6 it works:
python
Python 2.6.6 (r266:84292, Aug 18 2016, 15:13:37)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-17)] on linux2
Type "help", "copyright", "credits" or "license" for more information.



import Tkinter



PLEASE NOTE, I know that the module is lower case t in Python 3 so instead of import Tkinter, I am typing import tkinter.
My question is: How do I install tkinter in Python 3 in CentOS.
This I what have tried so far:
yum install python3-tk
Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
 * base: mirror.us.leaseweb.net
 * extras: mirror.us.leaseweb.net
 * updates: mirror.us.leaseweb.net
Setting up Install Process
No package python3-tk available.
Error: Nothing to do
How do I install in CentOS 6 the module tkinter and make Python 3 able to use it?
Thanks for any feedback.
If you want to install tkinter in order to use matplotlib you may try 

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

It worked for me
How to install tkinter in python 3.6 in CentOS release 6.4