RuntimeError: Invalid DISPLAY variable

Question

I am running my python script in another machine by using ssh command in linux. I have also run this command :

source ~/.bashrc 

after logging in the other machine, in order to define the proper paths in the new machine. I was getting the error message for running the following python code lines even I have tried to follow the instruction in this question by defining the backend.

>>> import matplotlib
>>> import pylab as plt
>>> matplotlib.use('Agg')
>>> import numpy as np
>>> x=np.arange(0,2,0.001)
>>> y=np.sin(x)**2+4*np.cos(x)
>>> fig = plt.figure()
>>> plt.plot(x,y,'r.')     

The error message

This probably means that Tcl wasn't installed properly.
Traceback (most recent call last):
  File "Systematic_Optimised.py", line 513, in <module>
    fig = plt.figure()
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/pyplot.py", line 435, in figure
    **kwargs)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 47, in new_figure_manager
    return new_figure_manager_given_figure(num, thisFig)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 54, in new_figure_manager_given_figure
    canvas = FigureCanvasQTAgg(figure)
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 72, in __init__
    FigureCanvasQT.__init__(self, figure)
  File "/vol/aibn84/data2/zahra/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt4.py", line 68, in __init__
    _create_qApp()
  File "/vol/anaconda/lib/python2.7/site-packages/matplotlib/backends/backend_qt5.py", line 138, in _create_qApp
    raise RuntimeError('Invalid DISPLAY variable')
RuntimeError: Invalid DISPLAY variable

any suggestion how to fix the problem

Solution 1

You must declare matplotlib.use('agg') before import pylab as plt.

Reference

Solution 2

Add

plt.switch_backend('agg')

after

import matplotlib.pyplot as plt

Comments

[Hana90]

still I have the runtime error :( File "/home/user/anaconda2/lib/python2.7/site-packages/matplotlib‌​/backends/backend_qt‌​5.py", line 138, in _create_qApp raise RuntimeError('Invalid DISPLAY variable') RuntimeError: Invalid DISPLAY variable

[Mauro Baraldi]

Take a look at this comment

[Michelle Owen]

it seems you should use lower case 'a', so do matplotlib.use('agg') before import pylab as plt.

[Mauro Baraldi]

@MichelleOwen have you tested? I cannot test it now!

[Michelle Owen]

@MauroBaraldi yes, I did. At least it worked for me.

[fr_andres]

worked for me too in a virtual environment after having to pip install PySide. Thanks a lot!

[teichert]

For me, import matplotlib; matplotlib.use('agg') didn't fix the error, but import matplotlib; matplotlib.pyplot.switch_backend('agg') did (as suggested here).

[Hugh Perkins]

Thanks! This plays much more nicely with pylint :)

[pacificgilly1992]

This is fantastic, now I can switch the backends depending on how I run the code. I have a problem when using 'agg' which stops showing the plot in the command window which can sometimes be disappointing. Therefore, I can switch out the backend for my uses.