Add this to the bottom of your code.
if __name__ == "__main__":
main()
See https://docs.python.org/2/library/main.html
Main needs to be called explicitly. You can do it without the if statement, but this allows your code to be either a module or a main program. If it is imported as a module, main() won't be called. If it is the main program then it will be called.
You are thinking like a C programmer. In this case python acts more like a shell script. Anything not in a function or class definition will be executed.
