Using Matplotlib when DISPLAY is undefined [duplicate]

Question

When using Matplotlib on a remote machine (e.g. on Travis CI), I run into frequent runtime errors related to the DISPLAY environmental variable not being set. As recommended, I have set the Agg backend via matplotlib.use at the beginning of my test scripts, and have ensured there are no calls to show(). Nevertheless, I still get errors such the following:

Traceback (most recent call last):
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/travis/build/pymc-devs/pymc/pymc/tests/test_plots.py", line 36, in test_multichain_plots
    forestplot(ptrace, vars=['early_mean', 'late_mean'])
  File "/home/travis/build/pymc-devs/pymc/pymc/plots.py", line 325, in forestplot
    interval_plot = subplot(gs[0])
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/pyplot.py", line 896, in subplot
    fig = gcf()
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/pyplot.py", line 450, in gcf
    return figure()
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/pyplot.py", line 423, in figure
    **kwargs)
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 31, in new_figure_manager
    return new_figure_manager_given_figure(num, thisFig)
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 38, in new_figure_manager_given_figure
    canvas = FigureCanvasQTAgg(figure)
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/backends/backend_qt4agg.py", line 70, in __init__
    FigureCanvasQT.__init__( self, figure )
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/backends/backend_qt4.py", line 207, in __init__
    _create_qApp()
  File "/home/travis/anaconda/envs/testenv/lib/python2.7/site-packages/matplotlib/backends/backend_qt4.py", line 62, in _create_qApp
    raise RuntimeError('Invalid DISPLAY variable')
RuntimeError: Invalid DISPLAY variable

Are there other recommendations to averting this?

Answer 1

Using xvfb works, see Travis's GUI & Headless browser testing documentation.

p.s. The matplotlib.use('Agg') trick works for me.