[python] No plot window in matplotlib

I just installed matplotlib in Ubuntu 9.10 using the synaptic package system. However, when I try the following simple example

>>> from pylab import plot;
>>> plot([1,2,3],[1,2,3])
[<matplotlib.lines.Line2D object at 0x9aa78ec>]

I get no plot window. Any ideas on how to get the plot window to show?

If you are starting IPython with the --pylab option, you shouldn't need to call show() or draw(). Try this:

ipython  --pylab=inline

If you encounter an issue in which pylab.show() freezes the IPython window (this may be Mac OS X specific; not sure), you can cmd-c in the IPython window, switch to the plot window, and it will break out.

Apparently, future calls to pylab.show() will not freeze the IPython window, only the first call. Unfortunately, I've found that the behavior of the plot window / interactions with show() changes every time I reinstall matplotlib, so this solution may not always hold.

Any errors show up? This might an issue of not having set the backend. You can set it from the Python interpreter or from a config file (.matplotlib/matplotlibrc) in you home directory.

To set the backend in code you can do

import matplotlib
matplotlib.use('Agg')

where 'Agg' is the name of the backend. Which backends are present depend on your installation and OS.

http://matplotlib.sourceforge.net/faq/installing_faq.html#backends

http://matplotlib.org/users/customizing.html

Modern IPython uses the "--matplotlib" argument with an optional backend parameter. It defaults to "auto", which is usually good enough on Mac and Windows. I haven't tested it on Ubuntu or any other Linux distribution, but I would expect it to work.

ipython --matplotlib

The code snippet below works on both Eclipse and the Python shell:

import numpy as np
import matplotlib.pyplot as plt

# Come up with x and y
x = np.arange(0, 5, 0.1)
y = np.sin(x)

# Just print x and y for fun
print x
print y

# Plot the x and y and you are supposed to see a sine curve
plt.plot(x, y)

# Without the line below, the figure won't show
plt.show()

If you are user of Anaconda and Spyder then best solution for you is that :

Tools --> Preferences --> Ipython console --> Graphic Section

Then in the Support for graphics (Matplotlib) section:

select two avaliable options

and in the Graphics Backend:

select Automatic

Try this:

import matplotlib
matplotlib.use('TkAgg') 

BEFORE import pylab

--pylab no longer works for Jupyter, but fortunately we can add a tweak in the ipython_config.py file to get both pylab as well as autoreload functionalities.

c.InteractiveShellApp.extensions = ['autoreload', 'pylab']
c.InteractiveShellApp.exec_lines = ['%autoreload 2', '%pylab']

pylab.show() works but blocks (you need to close the window).

A much more convenient solution is to do pylab.ion() (interactive mode on) when you start: all (the pylab equivalents of) pyplot.* commands display their plot immediately. More information on the interactive mode can be found on the official web site.

I also second using the even more convenient ipython -pylab (--pylab, in newer versions), which allows you to skip the from … import … part (%pylab works, too, in newer IPython versions).

Another possibility when using easy_install is that you need to require the most recent version of matplotlib. Try:

import pkg_resources
pkg_resources.require("matplotlib")

before you import matplotlib or any of its modules.