TclError: no display name and no $DISPLAY environment variable

TclError: no display name and no $DISPLAY environment variable

$ python script.py
Traceback (most recent call last):
  ...
_tkinter.TclError: no display name and no $DISPLAY environment variable

Why this happens

This error occurs when you try to generate plots using a GUI backend (like TkAgg) on a server or a headless environment (like a Docker container or SSH session) that doesn’t have a display attached.

Fix

Configure Matplotlib to use a non-interactive backend like Agg before importing pyplot, or set the backend in your matplotlibrc.

Wrong code

import matplotlib.pyplot as plt
plt.plot([1, 2, 3])
plt.show()

Fixed code

import matplotlib
matplotlib.use('Agg') # Set backend before importing pyplot
import matplotlib.pyplot as plt

plt.plot([1, 2, 3])
plt.savefig('plot.png') # Save instead of show