"UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure." Is Displayed When Quantizing an Object Detection Network

Symptom

When an object detection network is quantized, the "UserWarning: Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure." message is displayed. As a result, the quantized detection result is not displayed on the GUI.

Possible Cause

The possible cause is that the Tkinter is not installed. You can run the following command in the Python terminal to verify the installation. If the following information is displayed, the Tkinter is not installed successfully.

hisisoc@ubuntu62:~$ python3.7.5
Python 3.7.5 (default, Mar  3 2020, 13:58:02)
[GCC 7.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tkinter
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/python3.7.5/lib/python3.7/tkinter/__init__.py", line 36, in <module>
    import _tkinter # If this fails your Python may not be configured for Tk
ModuleNotFoundError: No module named '_tkinter'

Solution

If the Tkinter fails to be installed by installing python3-tk, the possible cause is that multiple Python 3 versions are installed or the tk-dev library fails to be installed. If the tk-dev library fails to be installed, perform the following steps:

1. Run the following command to reinstall the tk-dev library:

   sudo apt-get install tk-dev

2. Go to the Python 3.7.5 installation directory and recompile and install Python 3.7.5.

   cd Python-3.7.5
   ./configure --prefix=/usr/local/python3.7.5 --enable-shared
   make 
   sudo make install

3. Delete the original soft links.

   sudo rm -rf  /usr/bin/python3.7.5 
   sudo rm -rf  /usr/bin/pip3.7.5
   sudo rm -rf  /usr/bin/python3.7 
   sudo rm -rf  /usr/bin/pip3.7

4. Set the soft links again.

   sudo ln -s /usr/local/python3.7.5/bin/python3 /usr/bin/python3.7.5 
   sudo ln -s /usr/local/python3.7.5/bin/pip3 /usr/bin/pip3.7.5
   sudo ln -s /usr/local/python3.7.5/bin/python3 /usr/bin/python3.7 
   sudo ln -s /usr/local/python3.7.5/bin/pip3 /usr/bin/pip3.7

5. Verify the installation again. If import tkinter is displayed, the installation is successful.

   hisisoc@ubuntu62:~$ python3.7.5
   Python 3.7.5 (default, Mar  3 2020, 13:58:02)
   [GCC 7.4.0] on linux
   Type "help", "copyright", "credits" or "license" for more information.
   >>> import tkinter
   >>>