You can test an existing ROOT installation if it provides python bindings. Try “root-config --features” and see if the output contains “python”, or try “root-config --has-python” and see if you get “yes”.
If your current ROOT installation does not provide python bindings, you need to rebuild it from scratch, configuring it with “–enable-python” (note: “binary” and “development” packages of python >= 2.2 required). After the “configure” step, make sure that the “config.log” file contains “Result: Enabled support for … python, …” somewhere near its end.