matplotlib plot doesn't appear even after editing the backend and using pylab.show()

Question

I have a simple script to test a plot in matplotlib but no window showing the figure appears. On reading other questions on stackoverflow, I've done the following to resolve this:

• installed PySide using these instructions.

• edited matplotlibrc file with these two lines:

   backend      : Qt4Agg
   #backend.qt4 : PySide        # PyQt4 | PySide
  

  so that the command python -c 'import matplotlib; import matplotlib.pyplot; print(matplotlib.backends.backend)' now yields Qt4Agg whereas before it gave agg

• included the pylab.show() command. So the set of commands that I now tried in the python interpreter after installing Pyside, and editing the matplotlibrc file look like this:

    import pylab
    pylab.ion()
    import matplotlib.pyplot as plt
    import numpy as np
    x = np.arange(0,5,0.1)
    y = np.sin(x)
    plt.plot(x,y)
   [<matplotlib.lines.Line2D object at 0x7fcef627cdd0>]
   pylab.show()
  

  However, the plot still doesn't show. Could anyone please help me with this? I am using Ubuntu 14.04 in VirtualBox with python2.7.

Answer 1

When I use your code the plot actually flashes on the screen, but closes immediately. Placing an input() function at the end might help you with debugging it:

import pylab
import matplotlib.pyplot as plt
import numpy as np


pylab.ion()
x = np.arange(0,5,0.1)
y = np.sin(x)
plt.plot(x,y)
pylab.show()
tin = input("Test Input: ")

And removing the pylab.ion() actually keep the plot on the screen. This gives you another hint. There are already some good answers why this is happening. E.g.:

• Matplotlib ion() function fails to be interactive