If you want to plot in an environment without configured X11 you cannot just import matplotlib.pyplot, because you will get an error message like

no display name and no $DISPLAY environment variable

. But there is a solution if you want to use SSH without X-forwarding, run plotting scripts on a cluster or just in a tmux has by accident not set the DISPLAY variable.

You need to set the Backend to Agg before importing pyplot:

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

So you might want to have a snippet that works remote without X and locally. For this you can check the environment variables

import os
if not os.environ.get("DISPLAY", False):
    import matplotlib as mpl
    mpl.use("Agg")
import matplotlib.pyplot as plt

via Stackoverflow