"_tkinter.TclError: no display name and no $DISPLAY environment variable"

This error typically occurs when running a Python script using Matplotlib on a server without a graphical display. Matplotlib relies on a backend to render plots, and by default, it chooses the Xwindows backend, which requires a graphical display.

To resolve this issue, you need to instruct Matplotlib to use a non-interactive backend, such as Agg. Here's how you can achieve that:

• Add the following code at the beginning of your script, before importing pyplot:

import matplotlib
matplotlib.use('Agg')

This code sets the matplotlib backend to Agg, which is suitable for generating static images without a display.

• Alternatively, you can add the following line to your .config/matplotlib/matplotlibrc file:

backend: Agg

This will permanently use the Agg backend for your Python scripts.

• If you are connecting to the server remotely, use the following command:

ssh -X remoteMachine.com

This command will enable X11 forwarding, allowing you to use a display on the server.

• You can also try exporting the DISPLAY variable:

export DISPLAY=mymachine.com:0.0

This will set the DISPLAY environment variable, which is required for the Xwindows backend.

For more information on using Matplotlib on servers, refer to the documentation: https://matplotlib.org/faq/howto_faq.html#matplotlib-in-a-web-application-server