DISPLAY error matplotlib

When error occur about this "$DISPLAY not set" when you run python code that use matplotlib this happened because your matplotlib backend is set to FltkAgg, GTK, GTKAgg, GTKCairo, TkAgg , Wx or WxAgg they required a GUI that why error occur.

To solve this you must specific other backend that not required GUI (Agg, Cairo, PS, PDF or SVG) when use matplotlib like this

• In code
  

 import matplotlib
 matplotlib.use('Agg')

• In command line use -d option
  

python subplot_demo.py -dAgg

Remember when call savefig('filename') don't give it extension this will handle by backend that you specific e.g Agg will create file filename.png

source from --> http://matplotlib.sourceforge.net/backends.html