Generating figures with matplotlib when DISPLAY variable is undefined or invalid

[zhengtaoxiao]

When running the "metaplots" or "plot_orf_density" command, some users received errors similar to the following:

"raise RuntimeError('Invalid DISPLAY variable')"
_"tkinter.TclError: no display name and no $DISPLAY environment variable"

The main problem is that default backend of matplotlib is unavailable. The solution is to modify the backend. A very simple solution is to set the MPLBACKEND environment variable, either for your current shell or for a single script:

export MPLBACKEND="module://my_backend"

Giving below are non-interactive backends, capable of writing to a file:

• Agg
• PS
• PDF
• SVG
• Cairo
• GDK

See also:
http://matplotlib.org/faq/usage_faq.html#what-is-a-backend
http://matplotlib.org/users/customizing.html#the-matplotlibrc-file
http://stackoverflow.com/questions/2801882/generating-a-png-with-matplotlib-when-display-is-undefined