Add install requirement for Python (#369)

* Add install requirement for Python

* Add python3

* fixes

* fixes

* fix

Author: ilanbiala

Makefile

@@ -1,6 +1,7 @@
 .PHONY: clean install analysis test test-install develop docs docs-install
 
 venv:
+	@python --version || (echo "Python is not installed, please install Python 2 or Python 3"; exit 1);
 	virtualenv --python=python venv
 
 install: venv