How to use :

Get the HEPTutorial tarball and untar it

	wget http://ippog.web.cern.ch/sites/ippog.web.cern.ch/files/HEPTutorial.tar_.gz
	tar -xvzf HEPTutorial.tar_.gz

Setup root and pyroot

	source setup.sh

link and compile the classes, it also links the root input files

	source mk_links.sh

run the python script (here for mc_dy.root)

	python analysis.py mc_dy

contemplate the wonderful histogram you did (here in histos_mc_dy.root)