[Python-modules-team] Bug#548874: Bug#548874: matplotlib: figure() call fails. GTK seems not to recognise filetype of a .svg file

[Jonas]

hi,

as the original backtrace indicates, the svg problem is related to the gtkagg 
backend (which is default), in particular to the window icon:

/usr/lib/pymodules/python2.5/matplotlib/backends/backend_gtk.pyc in 
__init__(self, canvas, num)
    441         self.window.set_title("Figure %d" % num)
    442         if (window_icon):
--> 443             self.window.set_icon_from_file(window_icon)
    444
    445         self.vbox = gtk.VBox()

GError: Couldn't recognize the image file format for file 
'/usr/share/matplotlib/mpl-data/images/matplotlib.svg'

(see the original post for full backtrace)

> I tried to replicate this problem in a clean chroot and only maplotlib
> installed (and its dependencies of course) but the svg file is
> generated correctly *without* any svg library installed.
> 
> The code I used is:
> 
> import matplotlib as mpl
> mpl.use('SVG')
> import matplotlib.pyplot as plt
> plt.figure()
> plt.plot([1,2])
> plt.savefig('test.svg')

> python -c "import matplotlib as mpl ; print mpl.__version__"
> 0.99.0

same version as i have.

The problem arises when GTK creates a window and is told to load an icon in 
SVG format for which GTK needs a gdk-pixbuf loader for SVG. This is provided 
by librsvg2-common.
When using the matplotlib svg backend, no window will be created at all.
When using the qt4agg backend, the window is provided by QT instead of GTK, 
and the error also won't occur.
To reproduce this problem, deinstall librsvg2-common and use the following 
python code:

import matplotlib as mpl
# explicitly set gtkagg as backend. usually it is default
mpl.use('gtkagg')
import matplotlib.pyplot as plt
plt.figure()

as librsvg2-common is amongst the dependencies of gnome you usually won't see 
this error if you have gnome installed, which is default for debian.