How can I set the 'backend' in matplotlib in Python?

Question

I am new user of matplotlib, my platform is Ubuntu 10.04 Python 2.6.5

This is my code

import matplotlib matplotlib.use('Agg') import matplotlib.pyplot as plt  plt.plot([1,2,3]) 

The error is:

/usr/local/lib/python2.6/dist-packages/matplotlib/backends/__init__.py:41: UserWarning:  Your currently selected backend, 'agg' does not support show(). Please select a GUI backend in your matplotlibrc file ('/usr/local/lib/python2.6/dist-packages/matplotlib/mpl-data/matplotlibrc') or with matplotlib.use()   (backend, matplotlib.matplotlib_fname())) 

• I installed the Anti-Grain Geometry library apt-get install libagg but it is doesn't work.
• I tried to use other argument of backend like 'GTK' and 'TkAgg'.
• I installed python-gtk2-dev package, but still the error is below.
• Can anyone tell me an executable backend argument and its dependency library?

Here is the error:

>>> matplotlib.use('GTK') >>> import matplotlib.pyplot as plt Traceback (most recent call last):   File "<stdin>", line 1, in <module>   File "/usr/local/lib/python2.6/dist-packages/matplotlib/pyplot.py", line 95, in <module>     new_figure_manager, draw_if_interactive, show = pylab_setup()   File "/usr/local/lib/python2.6/dist-packages/matplotlib/backends/__init__.py", line 25, in pylab_setup     globals(),locals(),[backend_name])   File "/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_gtk.py", line 28, in <module>     from matplotlib.backends.backend_gdk import RendererGDK, FigureCanvasGDK    File "/usr/local/lib/python2.6/dist-packages/matplotlib/backends/backend_gdk.py", line 29, in <module>     from matplotlib.backends._backend_gdk import pixbuf_get_pixels_array ImportError: No module named _backend_gdk 

Answer 1

Your currently selected backend, 'agg' does not support show().

AGG backend is for writing to file, not for rendering in a window. See the backend FAQ at the matplotlib web site.

ImportError: No module named _backend_gdk

For the second error, maybe your matplotlib distribution is not compiled with GTK support, or you miss the PyGTK package. Try to install it.

Do you call the show() method inside a terminal or application that has access to a graphical environment?

Try other GUI backends, in this order:

• TkAgg
• wxAgg
• Qt5Agg
• Qt4Agg

Answer 2

FYI, I found I needed to put matplotlib.use('Agg') first in Python import order. For what I was doing (unit testing needed to be headless) that meant putting

import matplotlib matplotlib.use('Agg') 

at the top of my master test script. I didn't have to touch any other files.