[python] _tkinter.TclError: no display name and no $DISPLAY environment variable

I am running a simple python script in the server:

import matplotlib.pyplot as plt
import numpy as np

x = np.random.randn(60)
y = np.random.randn(60)

plt.scatter(x, y, s=20)

out_png = 'path/to/store/out_file.png'
plt.savefig(out_png, dpi=150)

I try to use the command python example.py in this server which has matplotlib 1.5.1 installed it fails with the error:

Traceback (most recent call last):
  File "example.py", line 7, in <module>
    plt.scatter(x, y, s=20)
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/pyplot.py", line 3241, in scatter
    ax = gca()
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/pyplot.py", line 928, in gca
    return gcf().gca(**kwargs)
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/pyplot.py", line 578, in gcf
    return figure()
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/pyplot.py", line 527, in figure
**kwargs)
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/backends/backend_tkagg.py", line 84, in new_figure_manager
    return new_figure_manager_given_figure(num, figure)
  File "/home/USER/.virtualenvs/nnet/lib/python2.7/site-packages/matplotlib/backends/backend_tkagg.py", line 92, in new_figure_manager_given_figure
    window = Tk.Tk()
  File "/usr/local/lib/python2.7/lib-tk/Tkinter.py", line 1810, in __init__
    self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: no display name and no $DISPLAY environment variable

What is happening here?

Another solution is to install Xvfb, and export your display to it. ie:

disp=:8
screen=0
geom=640x480x24
exec Xvfb $disp -screen $screen $geom 2>/tmp/Xvfb.log &

Then

$ export DISPLAY=:8

$ ./example.py

I also met this problem while using Xshell to connect Linux server.

After seaching for methods, I find Xming + Xshell to solve image imshow problem with matplotlib.

If solutions aboved can't solve your problem, just try to download Xming under the condition you're using Xshell. Then set the attribute in Xshell, SSH->tunnel->X11transfer->choose X DISPLAY localhost:0.0

I had this same issue trying to run a simple tkinter app remotely on a Raspberry Pi. In my case I did want to display the tkinter GUI on the pi display, but I want to be able to execute it over SSH from my host machine. I was also not using matplotlib, so that wasn't the cause of my issue. I was able to resolve the issue by setting the DISPLAY environment variable as the error suggests with the command:

export DISPLAY=:0.0

A good explanation of what the display environment variable is doing and why the syntax is so odd can be found here: https://askubuntu.com/questions/432255/what-is-display-environment-variable

You can solve it by adding these two lines in the VERY beginning of your .py script.

import matplotlib
matplotlib.use('Agg')

PS: The error will still exists if these two lines are not added in the very beginning of the source code.

In order to see images, plots and anything displayed on windows on your remote machine you need to connect to it like this:

ssh -X user@hostname

That way you enable the access to the X server. The X server is a program in the X Window System that runs on local machines (i.e., the computers used directly by users) and handles all access to the graphics cards, display screens and input devices (typically a keyboard and mouse) on those computers.

More info here.

I want to add an answer here that noone has explicitly stated with implementation.

This is a great resource to refer to for this failure: https://matplotlib.org/faq/usage_faq.html

In my case, using matplotlib.use did not work because it was somehow already set somewhere else. However, I was able to get beyond the error by defining an environment variable:

export MPLBACKEND=Agg

This takes care of the issue.

My error was in a CircleCI flow specifically, and this resolved the failing tests. One wierd thing was, my tests would pass when run using pytest, however would fail when using parallelism along with circleci tests split feature. However, declaring this env variable resolved the issue.

To add up on the answer, I used this at the beginning of the needed script. So it runs smoothly on different environments.

import os
import matplotlib as mpl
if os.environ.get('DISPLAY','') == '':
    print('no display found. Using non-interactive Agg backend')
    mpl.use('Agg')
import matplotlib.pyplot as plt

Because I didn't want it to be alsways using the 'Agg' backend, only when it would go through Travis CI for example.